CN105702138A - High-frequency circuit practical training device - Google Patents

Abstract

The invention discloses a high-frequency circuit practical training device. A classical high-frequency practical circuit is combined, multiple high-frequency electronic circuit modules are integrated in a practical training box, multiple anti-interference technologies are applied, and each module works independently and does not interfere mutually. The experimental box is composed of a transistor oscillator circuit, an AM transmitter circuit, an AM receiver circuit, an FM transmitter circuit, an FM receiver circuit, an FSK modulation circuit, an FSK demodulation circuit, a CPLD frequency meter circuit, a system power circuit module and the like. The main signal of each module circuit leads out a corresponding test terminal, students can further understand and learn the high-frequency electronic circuit through observing the signal parameters of the test terminal, each module is close to the practice, and the practicality and the applicability are strong.

Description

High-frequency circuit actual training device

High-frequency circuit actual training device of the present invention belongs to electronic information field。

Invent and make the actual training device being suitable for radio debugging technique real training, vocational skills training and the corresponding work post of verification of professional technical ability, in conjunction with classical high-frequency circuit, student can pass through real training and better grasp the theoretical knowledge learned, require understandable easy to learn, can by crucial acquisition of signal point be measured parameter, deepen Reinforcement Theory knowledge further by analysis waveform and parameter, make high frequency theoretical knowledge practiceization。Invention process first adopts omnipotent brassboard to overlap each corresponding modular circuit, and the instrument and equipment that room provides by experiment recalls each modular circuit, each parameter index of writing circuit one by one；Then schematic diagram and the pcb board figure of each modular circuit is drawn with ProtelDXP software；Then the pcb board figure of each module is combined, and open plate and be processed into printed circuit board；To the printed circuit board workflow by signal and each module characteristic welds one by one and debugging module circuit；Require that debugging and amendment are thus reaching the requirement of the relevant art index of each module；The outward appearance of concurrent camera-lucida body and size；Finally complete training box。

System invention demonstration and selection

Adopt the invention of unit element circuit, the actual training device of combination of wireless telecommunication is carried out again with connection wire, such advantage is functional module elements, student deepens the study to high-frequency circuit and understanding by unit circuit, and signal is also easy to test and regulates, but when being combined into corresponding functional module, more because connecting wire, comparatively mixed and disorderly to student's sensation on the one hand, there is also certain interference simultaneously, and radio communication is comparatively sensitive to interference signal reflection。

Adopt the integrated corresponding functional module of element circuit, each module is relatively independent in system, and the connection wire between module is less, is the transmission relation between final stage, element circuit in functional module is not had and disturbs, make experimental system more succinct simultaneously yet；The advantage that invention absorbs invention one on the other hand, utilize short-circuiting terminal that the element circuit in functional module is separated, so namely element circuit can be tested and invent, it is also possible to form specific wireless transmission communication system by relatively independent functional module。

FM radiating circuit invention invention demonstration and selection

Invention one: adopt monolithic FM transmission integrated circuit MC2833 and interlock circuit composition。It may make up the power amplifier launching high-frequency signal。But the resonant tank related to due to this chip is more, not easily tracking, thus frequency is wayward, causes jitter, easy treadmill, it is achieved comparatively difficulty。

Invention two: adopt integrated chip BA1404 and interlock circuit to constitute。It is mainly by audio preamplifier, stereo modulator, FM manipulator and radio frequency amplifier composition。Internal reference voltage is utilized to change the capacitance of varactor, it may be achieved the adjustment of tranmitting frequency。Typical case's frequency modulation frequency range is 75-108MHz。

In sum, selection invention two of the present invention, namely utilize integrated chip BA1404 to realize FM radiating circuit。

FM receives radiating circuit invention invention demonstration and selects

Adopt the chip MC3362 that MOTOROLA company of the U.S. produces。This chip is that monolithic narrow-band FM receives circuit, is mainly used in speech communication and the wireless receiver of data transmission。The circuit such as oscillating circuit, mixting circuit, limiting amplifier, integral discriminator, field intensity instruction driving and carrier frequency detecting circuit are comprised in MC3362 sheet。There is low suppling voltage, low-power consumption, sensitivity high。But this circuit is relatively used for FM radio receiver, in the frequency range required, carry out debugging relative difficulty。

Adopt integrated chip CXA1238S。This chip internal comprises the links such as the preposition amplification of FM, stereo demodulation amplification, the amplification of FM intermediate frequency and frequency discrimination, especially have employed Phase Lock Technique in chip, thus has central stabilizer, tunes the advantages such as simple, strong interference immunity, circuit stability。

System is made up of nine high frequency real training circuit modules, respectively by transistor oscillating circuit, and AM transmitter circuitry, AM receiver circuit, FM transmitter circuitry, FM receiver circuit, FSK modulation circuit, Fsk demodulator, CPLD frequency counter circuit, system power supply circuit module etc. forms。

Modular circuit is invented

LC and the invention of transistor oscillating circuit

Element circuit is invented

The output of LC and transistor oscillating circuit is the carrier signal source of transmitter, it is desirable to its vibration is sufficiently stable。Generally using crystal oscillating circuit, wherein Q-value is up to tens thousand of, and its frequency stability is up to 10-5～10-6。Crystal oscillator JT and C1, C2, C3, VT1 constitute Colpitts oscillation circuit, and frequency of oscillation is 3.579MHz。R1, R2, R3 in circuit determines the quiescent point of transistor, and wherein R1 can adjust。When quiescent point is arranged, first set collector current ICQ, general ICQ and take 0.5～4mA, ICQ too conference and cause output waveform distortion, produce higher hamonic wave。If transistor β=60, ICQ=2mA, UEQ=(1/2 ~ 1/3) Ucc, then can calculate R1, R2, R3。Shown installation circuit, UBQ=8.3V, UEQ=7.7V in debugging。

Installation and debugging

During debugging crystal oscillator, should first disconnect crystal oscillator, make agitator nonoscillatory, then survey each step voltage of audion with circuit tester。UEQ should meet

UEQ/(R2+R3) ≈ ICQ=2mA

If being unsatisfactory for, then adjustable R1 value。The quiescent point of audion is debugged after correctly, then connect crystal oscillator, measure the frequency of oscillation of agitator and the amplitude of output voltage。Want selecting properly test point during measurement, make the input impedance output impedance much larger than circuit test access point of instrument。Also should meet load resistance RL, RL at outfan should be equal with the equivalent input impedance of next stage circuit。If the input impedance of instrument is higher, then optional A point is measured；If the input impedance of instrument is relatively low, then B point should being selected to measure, the value at this moment coupling electric capacity Co is about 20pF。

AM transmitter circuitry is invented

Invention thinking

Single-frequency point refers to the Frequency point that carrier frequency is fixed value launched and receive, and so in the factor launched with do not need consideration to cause amplifier performance different because wave band is different when receiving, simplifies invention difficulty。Either simplex refers to that transmitter receiver cannot receive when launching, and cannot launch when receiving, and namely once can only carry out a kind of operation, or launch, or receive。So, a transmitter receiver is only comparable to the combination of a transmitter and a receiver, controls the conversion launched with receive with a switch。For the simplicity invented, general transmitter receiver adopts amplitude modulation to launch and receives。

Operation principle and composition frame

Its operation principle is: the first local oscillation produces the intermediate-freuqncy signal of a fixed frequency, and its output is delivered in manipulator；Speech amplifying circuit amplifies the signal from microphone, and its output is also delivered in manipulator；Manipulator output is amplitude modulated intermediate-freuqncy signal, and this signal is mixed with the second local oscillation signal after intermediate frequency amplifier amplifies；Second local oscillator is the signal source of a changeable frequency, generally selects the second local frequency?O2 is first vibration frequency?O1 and transmitting carrier frequency?O1 sum；Frequency mixer exports through bandpass or low pass filter, makes output carrier frequency?C=o2-o1；CF signal is carried out the power amplification power to required transmitting by power amplifier level。

The key technical indexes

(1) operating frequency range

The operating frequency of some frequency AM transmitter is 3.579MHz。

(2) transmitting power

Generally referring to the power that transmitter is transported on antenna, only when the wavelength X of the length of antenna Yu tranmitting frequency can be compared, carrier wave could be launched by antenna effectively。Wavelength X and frequency?Relation be:

λ=с/

In formula, с is propagation velocity of electromagnetic wave, с=3 × 108m/s。

If the sensitivity S A=2 μ V of receiver, then the relation of communication distance S and transmitting power PA is such as shown in table 1-1。

The relation of transmitting power PA and communication distance S

PA/mV50100200300400500600700

S/km2.843.384.024.454.825.085.275.50

The transmitting power Po of this circuit >=150mW。

(3) modulation

Modulation is the coefficient that modulation signal controls carrier voltage amplitude variations, and its span is 0～1, generally in per cent, namely ranges for 0%～100%。The characteristic of non-linear distortion (envelope distortion) manipulator can not be followed modulation voltage linear change and be caused the non-linear distortion that envelope distortion is AM transmitter of modulated wave, generally requires less than 10%。Linear distortion keeps modulation voltage amplitude constant, and the modulation depth characteristic variations that change modulating frequency causes is called linear distortion。This circuit modulation degree be 50%。

(4) noise level

Noise level refers to when not modulating signal, noise the modulation depth produced and signal modulation depth ratio time maximum。The noise level of broadcast transmitter requires less than 0.1%, and the noise level of general communication equipment requires less than 1%。

(5) aggregate efficiency

The ratio of the general power P ' c that the general power PA that transmitter is launched consumes with it is called the aggregate efficiency η A of transmitter, namely

η A=PA/P ' c。Aggregate efficiency η >=40% of this circuit

Element circuit is invented

(1) modulation circuit

According to the meaning of the question and given main devices, selected analog multiplier MC1496 constitutes modulation circuit。

If u is Ω=U Ω mcos Ω t=U Ω mcos (2 π?Ω t)

Carrier wave uc=Ucmcos Ω t=Ucmcos (2 π?Ct)

It is multiplied with carrier wave uc plus direct current UDC:

uAM=UM(1+MacosΩt)cosωct

In formula, index of modulation Ma=U Ω M/UDC≤1, otherwise can produce excessive amplitude modulation。

The each pin function of MC1496 is as follows:

1), SIG+ signal input anode 2), GADJ gain-adjusted end

3), GADJ gain-adjusted end 4), SIG-signal input negative terminal

5), BIAS offset side 6), OUT+ positive current outfan

7), NC sky foot 8), CAR+ carrier signal input anode

9), NC sky foot 10), CAR-carrier signal input negative terminal

11), NC sky foot 12), OUT-negative current outfan

13), NC sky foot 14), V-negative supply

When arranging the quiescent biasing of MC1496, the audion within multiplier should be made all to be operated in magnifying state, and make quiescent point be in the midpoint of dc load line as far as possible。The static bias voltage of each pin when debugging。

Pin 12345681012

Voltage-6-6.5-6.5-6-10.4+6.9+0.5+0.5+6.9

(2) speech amplifying circuit

According to given main devices, uA741 is integrated operational amplifier, it is possible to it, low frequency voice is amplified。Its output voltage is:

(3) buffer circuit

The input impedance of emitter-follower is big, output impedance is little, can significantly improve the performance of circuit, and therefore, conventional emitter-follower makees buffer circuit。During invention emitter-follower, mainly consider the matching problem of input impedance and output impedance and front stage。

(4) power amplification circuit

The power amplifier that wide-band transformer does coupling circuit is utilized to be called wideband power amplifer。The high frequency transformer of the useful high frequency magnetic core coiling of common wide-band transformer and transmission transformer。Wideband power amplifer does not need tuned vibration loop, can obtain linear amplification, but efficiency eta is relatively low in very wide frequency range, and general only have about 20%。It is usually used as the intergrade of transmitter, to provide bigger exciting power。

Frequency-selective network is utilized to be called resonance amplifier as the power amplifier of load circuit, the scope according to amplifier current conduction angle, it is possible to be divided into Class A, Class B, Class C and class D constant power amplifier。Current lead-through angle θ is more little, and the efficiency of amplifier is more high。Typically by the class C power amplifier final stage as transmitter, to obtain bigger output and higher efficiency。

For the high frequency power amplifier circuit that is made up of two stage power amplifier。Wherein transistor VT1 is buffer stage, and transistor VT2 and high frequency transformer Tr1 forms wideband power amplifer, and transistor VT3 also frequency-selective network L3, C6 forms Class C tuned power amplifier。

1. wideband power amplifer

The determination of quiescent point Q:

UBQ=UCCR6/ (R5+R6)

UEQ=UBQ-0.7=ICQ(R7+R8)

UCEO=UCC-UEQ=UCC-ICQ(R7+R8)

Wideband power amplifer colelctor electrode output PC is:

PC=PH/ηT=1/2UCMICM

In formula, PH is the actual power in output loading；η T is transformator efficiency of transmission, is generally 0.75～0.85。

UCM=UCC-ICQR8-UCES

In formula, UCES is saturation voltage drop, is about 1V。

ICM≈ICQ

Transformer turn ratio K is:

K=[(η TR'H)/RH] 1/2

In formula, RH is that VT2 exports impedance；R'H is the input impedance of understage transistors VT3。

2. class C power amplifier

The base bias voltage of Class C power amplifier is that the DC component IE0 the utilizing emission current pressure drop produced on emitter resistance R10 provides, therefore is called autobias circuit。

Colelctor electrode fundamental voltage amplitude is:

UC1m=IC1m/RP

In formula, IC1m is colelctor electrode fundamental current amplitude；RP is collector load impedance。Colelctor electrode output is:

Pc=UC1mIC1m/2

The dc power of direct-current power supply is: in PD=UCCIC0 formula, and IC0 is the DC component of colelctor electrode pulse。

3. the coiling of high frequency transformer。

The magnetic core of high frequency transformer should adopt nickel zinc (NXO) ferrite, and can not use silicon sheet core, because stalloy iron loss when high-frequency work is excessive。When making high frequency transformer magnetic core with NXO 100 circular ferrite, operating frequency is up to tens megahertzs。After determining core material, its inductance value can be determined by the number of turn of L coil, and the number of turn is more many, and inductance value is more big。In order to reduce the impact of coil leakage inductance and distribution capacity, the number of turn should be as far as possible less, and turn-to-turn distance should be big as far as possible。

Installation and debugging

Circuit debugging first should adjust quiescent point at different levels respectively, then adjusts output signal step by step from prime level backward。

The test of manipulator

When surveying modulator circuit quiescent point, local oscillation signal UO=0 should be made, modulate signal U Ω=0。First survey the voltage U5 on MC1496 the 5th foot, adjust the value of R5, make | U5 |/R5=I0；Then measuring each static work voltage, its value should be worth roughly the same with invention。Add local oscillator voltage Uo=100mV, make modulation voltage U Ω=0, regulate RP3 and make MC1496 output signal be minima, then make U Ω=100mV, at this moment the output waveform recorded should be the repressed double-sideband signal waveform of carrier wave, then regulates the RP3 amplitude-modulated wave making output waveform be Ma=50%。

The block diagram of superhet crystal radio circuit and the oscillogram of signal at different levels。The radio that invention currently uses is essentially all superheterodyne radio set, is characterized in: former high frequency carrier through frequency changer circuit frequency conversion, to be transformed to the intermediate-freuqncy signal that unified frequency is relatively low by the radio signals that radio receives。Then amplify then through intermediate frequency, demodulation is reduced into acoustical signal。Superheterodyne radio set have highly sensitive, selectivity good, steady operation and other merits。

The key technical indexes

(1) operating frequency range

The operating frequency of AM transmitter is 3.579MHz。

(2) sensitivity

Receiver outfan is when meeting specified output and certain output signal-to-noise ratio, and the minimum signal voltage needed for receiver inlet is called the sensitivity of receiver。The sensitivity of AM receiver is generally 5～50 μ V。

(3) selectivity

Receiver selects useful signal from the signal (including interference signal) of the many different frequencies acted on receiver antenna, suppressing the ability of near by frequency signal disturbing to be called selectivity, generally near by frequency damping capacity is represented by three dB bandwidth and receiver with receiver reception signal simultaneously。Generally require that three dB bandwidth is not less than 6～9kHz, 40dB bandwidth and is not more than 20～30kHz。

(5) intermediate frequency rejection ratio

Receiver suppresses the ability of intermediate frequency interference to be called intermediate frequency rejection ratio。Representing intermediate frequency rejection ratio typically by the ratio that frequency input signal is sensitivity S IF and receiving sensitivity S during the machine intermediate frequency, in units of dB, namely intermediate frequency rejection ratio=20lg (SIF/S) dB decibels is more big, illustrates that anti-intermediate frequency interference performance is more strong。Generally require that intermediate frequency rejection ratio is more than 60dB。

(6) image-frequency rejection ratio

The rejection ability that receiver disturbs for image frequency (image frequency) is called image-frequency rejection ratio。Image frequency=S ± 2I

In formula,?S is signal frequency；?1 is IF-FRE。Local frequency being higher than to the receiver of signal frequency, its image frequency is?S+2I；For the local frequency receiver lower than signal frequency, its image frequency is?S-2I。Image-frequency rejection ratio is represented typically by the ratio that frequency input signal is sensitivity S IM and receiving sensitivity S during image frequency, generally in units of dB, i.e. image-frequency rejection ratio=20lg (SIM/S) dB

Decibels is more big, illustrates that the ability of anti-image interference is more strong。Usually require that image-frequency rejection ratio is more than 60dB。

(7) AGC control

Receiver utilizes its gain of carrier Control received in signal to ensure that the constant ability of output signal level is called AGC control。During measurement, generally making receiver input signal start to step up from certain setting, until receiver exporting change to certain setting (such as 3dB), the decibels that now incoming signal level increases is the AGC control of receiver。

(8) output

Receiver maximum non-distortion power in output loading is called output。

Element circuit is invented

(1) input circuit

Sensed the high-frequency signal obtained by magnetic antenna, be actually high-frequency carrier signal and selected to obtain being intended to receive radio signals through LC resonant tank。(for making radio obtain higher selectivity, sensitivity, suitable L1 and L2 turn ratio should be selected。Now the aerial coil of dress is ready-made has invented, it is desirable to student notes as far as possible, coil is not broken, and otherwise removes coil and reduces the number of turns and affects turn ratio)。

(2) frequency changer circuit

The high-frequency signal sent here by input circuit is amplitude-modulated wave, and the local oscillation frequency signal that local oscillation produces is persistent wave, obtains 465KHZ intermediate-freuqncy signal through frequency-selecting after mixing。Therefore converter stage Main Function is the intermediate-freuqncy signal that the high-frequency signal of amplitude modulation becomes amplitude modulation。It is only that carrier frequency changes before and after conversion, and signal envelope is constant。General vibration and the mixer action completing this machine with a frequency-converter tube。To mixing, it is desirable to be operated in inelastic region, electric current can not be too big, and otherwise conversion gain declines, but to local oscillator, more greatly, conversion gain height is easily starting of oscillation again for electric current, and cell voltage decline is not easily left alone without help shakes。But vibration can not be too strong, and wave distortion otherwise can be caused to hear " coughing up ", " coughing up " sound, and gain declines on the contrary, and generally selecting electric current is 0.4～0.6mA。

(3) intermediate frequency amplifies

In put the quality of level radio sensitivity, selectivity etc. had decisive influence。In to put level work frequency be 465KHZ, do load with LC resonant tank in parallel, therefore only when signal frequency is 465KHZ, shunt-resonant circuit voltage is maximum, therefore improves complete machine selectivity。Radio adopts in one-level sometimes puts (be generally in two grades and put) Single-tuned intermediate frequency amplifier, and selectivity and sensitivity are not necessarily very good, but return loss is little, easy to adjust, therefore Pocket Computer this circuit widely used。

(4) detector stage

Intermediate-freuqncy signal is still amplitude-modulated signal, through detector stage (by diode or triode detection), takes out audio signal from amplitude-modulated wave。If what select is audion, utilizing one of them PN junction to play big signal demodulator effect under non-linear working state, this pipe also carries out reflex low-frequency current amplification simultaneously。

(5) low put and power amplification

Audio signal after detection is delivered to low discharging grade and is carried out audio frequency amplification, then passes through input tranformer and delivers to push-pull power amplifier level and carry out power amplification, and output signal promotes speaker to send sound。The pipe work of push-pull power amplifier circuit is in Class B state。Ending when no signal, second engineman stream work when having a signal, therefore efficiency is high, but produces distortion at characteristic curve sweep when Class B is operated in small-signal。Therefore this machine circuit ground level when no signal also has certain bias, so as to be operated in class AB state, such efficiency is high, and output is big, and power saving。Subparameter is consistent by all means in requirement two。Wish when assembling selected。All have one to damage by all means, it is necessary to pairing choosing pipe。Notice during welding that two pipes weld, as rosin joint one is managed, cause a pipe job to produce serious distortion, and volume is greatly reduced。

Installation and debugging

(1) element introduction

The kind of the variable capacitance used by radio is much used herein is that difference holds duplex。Vibration connection is 68pF。Antenna connection is the medium-sized doubly-linked of 140PF。The one end being marked with " A " at dual capacitor is antenna connection, and the one end indicating " O " is vibration connection。Centre is that what to indicate " G " is earth terminal。The bar magnet of magnetic antenna is of a size of 55X13X5mm。Winding and the number of turns of coil are shown in circuit theory。Coil is all with the high strength enamelled wire coiling of Φ 0.13。Medium wave oscillator coil B2(magnetic cap is black) model be LF10-l；The model of intermediate-frequency transformer is TF10-1 and TF10-2。All with resonant capacitor in these two intermediate-frequency transformers。Magnetic cap in first intermediate-frequency transformer B3 is white, and the magnetic cap in the second intermediate-frequency transformer B4 is green。

Audion is all NPN type silicon materials plastic packaging pipe, and wherein BG1, BG2, BG3 all select 3DG201；BG4 can be selected for 3DG201 or 9014。Their β value should between 150～200；The β value of frequency-converter tube should not be too big, is typically in about 60 times；BG6 and BG7 can with 9013。Their β value is not less than 100。Diode is 1N4148。Resistance is all 1/8W carbon film electricity resistance。Electric capacity C4, C7, C8 are electrolysis condenser；C3 is dacron terylene condenser。All the other are ceramic capacitor。

(2) circuit is installed

According to the experimental circuit that laboratory provides, whether the kind of the provided element in checking experiment room, model and quantity is correct。Owing to radio element is many, circuit is more complicated, therefore when assembling, generally wants the assembling of one-level one-level。Wireless sequence is precisely contrary with signal flow, namely assembling process should from power amplifier level, set low before being followed successively by put, letter wave scale, in put level, agc circuit, be finally converter stage and input circuit, such rank groups is equipped with the adjustment and the test that are beneficial to circuit。

(3) working direct current at different levels is adjusted

Millivoltmeter it is connected in series between colelctor electrode and DC source, select corresponding range, regulate biasing resistor Rb, (general with a fixed resistance go here and there again a upper potentiometer), make the numerical value that millivoltmeter indicates reach the operating current of regulation, then pull down this fixing resistance and potentiometer measures all-in resistance。Change the fixed resistance of corresponding resistance again。Even if this one-level regulates。Note:

A: when adjusting DC point, radio no signal should be kept to input。All screw in for this dual capacitor or all screw out。

B: also should survey operating current after changing the resistance of fixed resistance value again。Finally it is also noted that and two test points in printed circuit are connected。

(4) IF-FRE (in tune week) is adjusted

The method adjusting IF-FRE has instrument testing method and audition method etc. multiple。

Instrument testing method turns on radio, opens big volume potentiometer, by the wireless whole precession of doubly-linked variable condenser, avoids extraneous signal。Being regulated on 465kHz by the output frequency of HF signal generator, modulating frequency 1000Hz, modulation is adjusted on 30%。High-frequency signal (465kHz) after low frequency modulations couples electric capacity by 0.01～0.047 μ F, by wireless Base injection, regulates the output of signal generator so as to be gradually increased by little, can not hear with the sound in speaker and be as the criterion。Regulate by week in the third level, carry out forward step by step。With the magnetic cap of noninductive bakelite or screwdriver turn intermediate-frequency transformer, oscillograph or millivoltmeter is made to obtain maximum output。Said process should adjust several times repeatedly。If there is self-excitation, neutralizing capacitance and middle all transformators to be readjusted。The value of neutralizing capacitance is generally about 2pF。

Audition method, when radio reception function uppick station broadcast, selects a radio signals, further according to adjustment method recited above, and the size of listening, while week in adjusting, from back to front, one-level one-level, repeatedly adjust several times, until sound is the loudest。Middle Zhou Jiben can be harmonized in this way。

(5) frequency range is adjusted

Adjustment to prepare graduated disc。First in 550～700 kilohertz range, select a radio station, such as select Central People's Broadcasting Station 639 kilo hertzs, reference mark dish that duplex is spun on this position of scale 639 kilo hertzs, adjust the magnetic core of medium wave vibration line chart (black), receive this radio station, and it is bigger to be transferred to sound。Then selecting the radio station of a given frequency in 1400～1600 kilohertz range, duplex is spun on the scale of this frequency by reference mark dish, regulates trimmer (i.e. trimmer in duplex) in oscillation circuit and receives this radio station and tuned up by sound。Owing to the frequency of high and low end can interact in adjustment, so low side adjusts inductance core, the work of high-end tune electric capacity repeatedly to be adjusted and could finally be harmonized several times

(6) tracking

Utilize the low auspicious radio station of uppick when adjusting frequency range。Tune dish magnetic antenna coil position on bar magnet, makes sound the loudest, reaches low side tracking。Utilize and be adjusted to the high-end radio station of uppick during frequency range, regulate the trimmer (on doubly-linked antenna trimmer even) in input circuit, make sound the loudest, to reach high-end tracking。Also the same with adjusting frequency range, it is necessary to high and low end adjusts several times repeatedly。

Detection fault is patient and painstaking, it is orderly to cool down。Detection is undertaken by step, is generally detected forward by rear class, first judges abort situation (signal injection method)。Looking up the fault point (potentiometry), incremental again, fixes a breakdown。Abstain to adjust disorderly and disorderly tear open, blindly scald weldering, cause repairing worse and worse。

5.1FM transmitter circuitry is invented

Invention thinking

By to invention demonstration, have selected BA1404 chip as FM transmitter chip, BA1404 is that special IC launched by the FM radio set that ROHM company of the U.S. produces；Its integrated level is high；The peripheral cell needed is few；Reliable operation；Supply voltage subject range width, remains to normal operation when being low to moderate 1.5V。The circuit of FM transmitter is invented according to chip internal structure。

Operation principle

The circuit theory of this machine wherein BA1404 is one piece of f-m stereo sound encoder and transmitting special IC, adopts 18 foot dual-inline package。Due to the running voltage of IC1 itself relatively low (1-3V), and hunting power is less, from power several milliwatts only of its 7 foot output, will obtain bigger power output and must pass through what power amplification。

Be made up of a high frequency efficient agitator N1 and peripheral element thereof, although the hunting power of this agitator is less, but because its efficiency is higher so that the transmitting range of transmitter also farther out, at opening up to 1 kilometer。External audio frequency signal is inputted by P1 end, and C3, R3 and C1, R4 etc. respectively constitute the preemphasis network of left and right acoustic channels, coordinates with the deaccentuator of receiver and can obtain good frequency response so that high audio response has a certain upgrade。The frequency of pilot signal is 19KHz, determined by the crystal between 5,6 feet, the stereo composite signal that 38KHz oscillator signal produces after L, R signal are carried out time-division multiplex modulation export by 14 feet, and simultaneously 38KHz oscillator signal also obtains the pilot signal of 19KHz after 1/2 frequency divider of integrated inside divides and exported by 13 feet。The pilot signal of stereo composite signal and 19KHz is overlapped respectively through after R2, C7 and R1, C12, high frequency generator is carried out frequency modulation by the base stage being coupled to N1 again by C18, the operating frequency of agitator drops within the scope of 88-108MHz, i.e. frequency modulation broadcasting frequency range, the high-frequency signal after modulation by the collapsible mast being directly anchored on circuit board to air-launched。So that circuit working stability, avoid frequency shift (FS) and ensure good tonequality, it is proposed with the maintenance-free battery that voltage is 12V/6Ah to power, and provide running voltage for this circuit after three-terminal voltage-stabilizing, when burning voltage is within the scope of 6-9V, this circuit can normal operation, when 9V voltage power supply, output improves relatively。

Single-stage vibration and single-stage radiating circuit is adopted due to the machine, antenna is also directly drawn by the colelctor electrode of N1, not past any buffering, for avoiding producing frequency drift because of external electromagnetic wave interference, except adopting above-described stabilized power source exclusive PCR, also require all of element strictly by mark value。The electric capacity of higher-order of oscillation part should select high frequency Leaded Ceramic Disc Capacitor, L1, L2 encloses with 10 around 5 circles with the high strength enamelled wire of Φ 0.51mm is close on the drill bit of Φ 3mm respectively, antenna adopts the collapsible mast of 1.2--1.5 rice, and make to be directly anchored to bottom it solder side of circuit board, the Copper Foil contacted with antenna bottom must weld the thin stannum of last layer in advance equably, and strengthen the contact area with antenna bottom as far as possible, at will with a wire, antenna bottom can't be connected with circuit board, so will result in high-frequency loss, shorten transmitting range, and it is easily introduced the interference in the external world, contact area should be strengthened during circuit board invention。As being intended to further reduce interference, can whole circuit be loaded in a shielding box, shielding box is made with the iron plate or tin plate with certain thickness (2-3mm), with barricade by IC1 partial circuit and high-frequency oscillating circuits isolation in box, the ground end stannum of box wall and circuit board encloses, and reserved antenna hole and audio frequency input hole, the lead-in wire of two-way audio signal adopts twin-core intertexture net shielding line。Source of sound can select the earphone of walkman, CD player or video disc player to export, and must attach volume control potentiometer to regulate volume output level, it is to avoid produces ovennodulation。

Installation and debugging

(1) main feature of BA1404

A. adopting low-voltage, low-power consumption invention, voltage is between 1～3V, and representative value is 1.25V, maximum power dissipation 500mW, b. quiescent current is 3mA；

C. by stereo modulation, FM modulation, radio frequency amplifying circuit integrated on a single die；

D. required peripheral cell is few；

E. two channel separations are high, and representative value is 45dB；

F. input impedance is 540 Ω (fin=1kHz), and input gain is 37dB (Vin=0.5mV)；

G. typical radio-frequency output voltage is 600mV。

(2) pin function and chip introduction

BA1404 is mainly by audio preamplifier (AMP), stereo modulator (MPX), FM manipulator and radio frequency amplifier composition。

The audio frequency amplifier of stereo prestage respectively two sound channels。When input is for 0.5mV, gain is up to 37dB, and bandwidth is 19kHz。As inputted the composition that there is frequency in signal higher than 19kHz, then must adding a low pass filter at input, otherwise the separating degree of two sound channels can decline。

In stereo modulation group, the 38kHz signal of agitator output is in stereo modulation。Generally connect an adjustable resistance at 16,17 feet, to obtain the channel separation degree of the best。Stereo mix signal (MPX exports signal) and pilot tone export the modulation signal after signal (PILOTOUT) synthesizes and enter radio-frequency oscillators by 12 feet and carrier wave is carried out FM modulation, output radiofrequency signal after radio frequency amplifies, the representative value of radiofrequency signal is at about 600mV。

A reference voltage unit VREF is additionally provided inside BA1404。Inventor can utilize this voltage signal to change the capacitance of external varactor, then changes the frequency of oscillation of carrier wave。Therefore, as long as the partial pressure value controlling a resistance just can reach to change the purpose of tranmitting frequency, this is the invention that comparison is unique。

During invention it should be noted that following some:

(1) in order to make the frequency response of transmitter and FM receiver be mutually matched, need to adding preemphasis network at input, its time coefficient is 50 μ s。

(2) at 13,14 feet, when the stereo mix signal of stereo modulator output and pilot signal synthesize, it is possible to cause the separating degree of stereo channel to worsen, so must be noted that the value of 12,13,14 foot peripheral cells。

FM receiver circuit is invented

Invention thinking

By to invention demonstration, have selected CXA1238M chip as low pressure amplitude modulation/f-m stereo sound reception integrated circuit, its internal amplitude-modulated portions includes and receives the repertoire to the output of detection audio frequency from antenna, frequency modulation part includes and receives the repertoire to stereo decoding, the output of left and right acoustic channels audio frequency from antenna, as long as external one piece of stereo audio power amplifier and a small amount of peripheral cell just can be assembled into a complete AM/FM stereo receiver。

Operation principle and composition frame

Adopt integrated chip CXA1238S。This chip internal comprises the links such as the preposition amplification of FM, stereo demodulation amplification, the amplification of FM intermediate frequency and frequency discrimination, especially have employed Phase Lock Technique in chip, thus has central stabilizer, tunes the advantages such as simple, strong interference immunity, circuit stability。

From the FM signal that antenna receives, through 87～108 GHz bandpass filters (BPF), be added to the 18 feet outputs of IC, deliver to internal FM pre-amplification circuit, put through height, be mixed after demodulate the intermediate-freuqncy signal of 10.7 megahertzs, and exported by 16 feet。The 20 external FM high-frequency amplifying tuning loops of foot, 22 feet are FM local oscillator resonant tank。Equally, amplitude-modulated signal injects (19) foot after being tuned by antenna input circuit, and local oscillation signal injects 24 feet, and after mixing and the preposition amplification of AM, 465 kilo hertzs of intermediate-freuqncy signals also deliver to 16 foot outfans。The 24 external AM oscillator coils of foot。

The 16 external two-way frequency-selective networks of foot, 14 feet of 465 kilo hertzs of AM intermediate-freuqncy signal feed-in IC, through intermediate-frequency transformer T1, intermediate-frequenkcy ceramic filter B1, are selected in a road, are added in internal AM and put and detector stage；Another road FM intermediate-freuqncy signal is put and frequency-discriminating circuit in 10.7 megahertzs of ceramic filter B2, feed-in 13 foot FM。The 26 external FM ceramic discriminator B3 of foot, its mid frequency is 10.7 megahertzs, so can save the adjustment of frequency discrimination S curve, but its colour code (expression frequency departure) must be consistent with B2。

The 15 external range switches of foot, by the effect of the internal FM/AM DC converting circuit of IC, select duty。It is FM wave band when S1 disconnects, is AM wave band during s1 ground connection。12 feet are the outfan coordinating instruction drive circuit so that when reception signal is maximum, external LED 1 indicates the brightest。

Stereo composite signal (or monophonic signal) after detection, controlled voltage by being transformed into AGC/AFC after direct current amplifier amplification, filtering in IC, 10 feet export, feed back to 23 feet by R1, for connecing the equivalent capacity of varactor in controlling, to reach to revise the effect of local oscillator。Change the capacity of external capacitor C7, it is possible to adjust the introducing scope of AFC。External capacitor C18 determines AGC time constant when AM receives。Stereo composite signal is amplified, delivers to stereo demodulator, phase discriminator 1 and phase discriminator 2 respectively。

Phase discriminator 1, voltage-controlled oscillator (VCO) (VCO) and frequency divider composition phase-locked loop。VCO produces the oscillator signal of 76 kilo hertzs, becomes 38 kilo hertzs of stereo demodulation switching signals after two divided-frequency, delivers to demodulator amplifier。Then through two divided-frequency, and 19 kilohertz signal after phase shift 90 ° carry out phase bit comparison with 19 kilo hertzs of pilot signals in composite signal in phase discriminator 1, export an error voltage。After being filtered radio-frequency component by external low pass filter (between 29 feet and 1 foot), for controlling frequency of oscillation and the phase place of VCO, until loop-locking。The free oscillation frequency of VCO can be finely tuned by 27 foot outer meeting resistances, thus adjusting the catching range of TPS Tracking Pilot Signal。

The effect of phase discriminator 2 is to detect stereo/monophonic switch controlling signal。When after frequency dividing, 19 kilohertz signal are identical with the frequency of input pilot signal, when phase contrast is zero, output positive voltage is maximum, after low-pass filtered device filtering (2,3 foot external capacitor) and direct current amplify, open " stereo/monophonic " switch, and the 4 external stereo indication light diode (LED)s 2 of foot are lighted in driving。It addition, 4 feet can also be used to detection VCO frequency of oscillation。

The left and right sound channels signal of output is amplified in demodulation, respectively from 6 feet and 5 outputs, delivers to input 2 foot and 3 feet of ULN3782M double power amplifier circuit。ULN3782M adopts 8 foot circular row straight cutting encapsulation, and volume is little, and peripheral cell is few, working power voltage scope 2～9 volts, and when VCC=6V, output is 430 Europe, milliwatt/8 and 240 Europe, milliwatt/16;When VCC=4.5V, output is 220 Europe, milliwatt/8 and 125 Europe, milliwatt/16。RP1-2 is stereo doubly-linked potentiometer, controls the volume of left and right sound channels, and XS is stereo jack, can be used for external stereophone or with to small-size sound box。

XA1238 is the radio integrated circuit of function admirable, inside has the height of AM, FM to put, is mixed, in put, detection, the function such as frequency discrimination and FM stereo decoding, automatic frequency control circuit, compared with the similar radio reception IC of other companies, sense of hearing also feels warm comfortable。Under towards everybody introduce each pin of this IC function describe:

29 feet are the loop filters of the phase locked loop oscillator of internal stereo decoding;

The oscillator signal that 3 feet are internal stereo decodings produces, it is necessary to when closing stereo, it is possible to connect a resistance over the ground at 2 feet;

4 feet are detection and the instructions of stereo decoded signals, receive stereo rear lantern festival bright;

6 feet are the output of left and right acoustic channels audio signal respectively;

7 feet are power supply foot, and the DC voltage of input 2-8V can normal operation;

8 feet are internal electric source filtering;

10 feet are the filtering that FM automatic frequency controls, and are then the filtering of automatic gain control circuit during AM, and electric capacity changes the time during court of a feudal ruler;

The 11 public foot ground connection of foot;

12 feet are adjusted and are called on instruction, and during adjustment radio station, this lamp is bright;

13 foot FM intermediate-freuqncy signal inputs, signal takes out audio signal then through frequency discrimination (fm demodulation) after amplifying;

14 foot AM intermediate-freuqncy signal inputs, signal takes out audio signal then through detection (demodulation) after amplifying;

The wave band switching of 15 foot AM, FM, should be directly grounded during for AM wave band;

16 foot FM/AM intermediate-freuqncy signal inputs, are then selected the signal of AM, FM by different frequency selectors;

The 17 public foot ground connection of foot;

18 foot FM aerial signal inputs, generally connect collapsible mast, and high-grade chance adds frequency-selective network, adds change-over circuit and connects exterior aerial;

19 foot AM aerial signal channel selection inputs, are typically all bar magnet coil, the electromagnetic wave (medium wave, shortwave) that directly sensing is aerial;

20 foot FM aerial signal channel selections are amplified, and the sensitivity of FM radio reception, selectivity are determined by inductance and the electric capacity of this foot;

21 foot internal reference mu balanced circuit 1.25V, height puts vibration biasing;

22 foot FM oscillation signal frequencies regulate, and produce the oscillator signal of 10.7MHz higher than radio station, receive frequency range thus foot and determine;

23 foot FM oscillator signal automatic frequency control circuits, inside is a varactor;

24 foot AM oscillation signal frequencies regulate, and produce the oscillator signal of 465KHz higher than radio station, receive frequency range thus foot and determine;

25 foot mute functions, adjust in platform process, and when not harmonizing, noise reduces volume time big automatically;

26 foot FM descriminator wave filter, it is intended that in order to reduce the audio signal of frequency modulation;

The 27 stereo voltage controlled oscillators of foot regulate, and this frequency is eventually subject to frequency modulation broadcasting neutral body acoustic conductance frequency decoding signal and controls;

28 foot control voltage filters。

(2) circuit debugging

This FM receiver adopts earphone cord to make antenna, the high-frequency signal sensed by earphone cord coupled to band filter BPF through C21, BPF filters out the high-frequency signal beyond 88-108MHz, fm broadcast signal then delivers to the base stage of V1, sent into antenna input the 18th foot of IC1 by C20 after V1 amplifies, and generation frequency is 10.7MHz intermediate-freuqncy signal after being mixed with integrated internal local oscillation signal, this intermediate-freuqncy signal is exported by 16 feet, in order to improve sensitivity and the selectivity of receiver, this circuit is also provided with the gain that one-level is made up of V2 and peripheral cell be 18db pre-in put, the intermediate-freuqncy signal of 16 foot outputs delivers to V2 through C23, exported by its colelctor electrode after V2 amplifies and filter out 10.7MHz intermediate-freuqncy signal through intermediate frequency discriminator CF2, 13 feet of IC1 are sent into by R7, then L is recalled by integrated Interior Solutions, R two-way audio signal is respectively by 5, 6 foot outputs, earphone jack P is delivered to after being done further power amplification by IC2 after volume potentiometer W, and promote earphone to send sound。

FSK modulation circuit is invented

FSK principle and signal produce frame

(1) FSK principle

Frequency shift keying (FSK) is to utilize Digital Signals carrier frequency to transmit information。Available digital baseband signal goes to control an analog switching circuit, for instance " 1 " code transmits frequency f1, and " 0 " code transmits frequency f2。Making its output frequency is alternate for f1 and f2 Sine Modulated waveform。

Element circuit is invented

Invented the modulation circuit of FSK by the principle of fsk signal waveform and FSK, circuit is made up of wave generator circuit, frequency dividing circuit, waveform translation circuit, analog switching circuit etc.。

(1) wave generator circuit

The crystal oscillating circuit that wave generator circuit is made up of 4096 reversers and 4.096MHZ produces the sine wave signal of 4.096MHZ。

(2) frequency dividing circuit

Frequency dividing circuit adopts the CD4042 digital frequency divider of two panels 14 frequency dividing to divide。Because wave generator circuit produces the sine wave signal of 4.096Mhz, and by 2KHz, fsk signal represents that signal 0 and 4KHz represent what signal 1 formed respectively, so original signal to be divided, invention have employed 7 grade of 128 frequency dividing CD4042 chip of two panels to form frequency dividing circuit。Thus the signal waveform of 2KHz, 4KHz, the 500Hz needed for obtaining module。

(3) waveform translation circuit

Waveform varying circuit is constituted waveform conversion by amplifier UA701 and peripheral resistance capacitance, the square-wave signal that frequency dividing circuit exports is transformed to sine wave signal, meets the requirement of the signal of modular circuit。Its principle is that square-wave signal is carried out shaping by the resistance capacitance composition charge-discharge circuit that make use of amplifier peripheral。。By formula:

=RC and=1/F determines R, C parameter value in circuit。

(4) analog switching circuit

Analog switching circuit adopts the CD4052 chip of Liang Zu tetra-tunnel input, and two-way carrier frequency produces fsk signal after the analog switch 4052 that digital baseband signal controls。

Fsk demodulator is invented

FSK demodulation principle and signal produce frame

(1) FSK demodulation principle

The demodulation of fsk signal is divided into coherent demodulation and non-coherent demodulation。Non-coherent demodulation is divided into frequency-discrimination method, zero passage detection method, differentiation etc.。

When adopting zero passage detection method, fsk signal, through amplifying amplitude limiter circuit, obtains pulse signal；After after differential shaping, obtain spike signal, its pulse number represents the number of times of fsk signal zero crossing。Obtain certain altitude and the square wave of certain pulsewidth through pulse shaper, the dutycycle of square wave is adjustable by RC circuit, and the mean direct component of signal is directly proportional to pulse recurrence frequency, is namely directly proportional to the carrier frequency of input signal。Low-pass filtered device follower exports its mean direct component, after judgement shaping, has both obtained demodulation original figure baseband signal。

In zero passage detection, two carrier frequency frequency differences are more big, and mean direct component is then more big, and interference free performance is also more good, but shared frequency band is also more wide。The selection principle of the cut-off frequency fc of low pass filter is:

f1<fc<f2

(2) FSK demodulates signal and produces frame。

Element circuit is invented

(1) amplify and amplitude limiter circuit invention

In zero passage detection; fsk signal amplifies amplitude limiter circuit through the 40106 of LM741 and 6 reversers with Schmidt trigger; obtain pulse signal; in circuit is invented; two Zener diodes and UA741 built-up circuit are used; their effect is amplitude limit, protects UA741 so that it is output amplitude is stable at 10V。

(2) differential, rectification, pulse shaping circuit are invented

This real training circuit adopts bistable multivibrator CD4098 once to complete differential, rectification, pulse shaping, it obtains certain altitude and the square wave of certain pulsewidth through pulse shaper, the dutycycle of square wave is adjustable by RC circuit, the mean direct component of signal is directly proportional to pulse recurrence frequency, is namely directly proportional to the carrier frequency of input signal。6 feet 4098 directly export pulse, and its pulse width is: 0.6RC。In 4098 outside suitable adding, peripheral circuit can form multivibrator, produces fixing rate-adaptive pacemaker。Obtaining spike after 4098 differential shapings, its pulse number represents the number of times of fsk signal zero crossing。

(3) low-pass filter circuit invention

Low pass filter adopts the low-pass filter circuit being made up of LM747 and peripheral resistance capacitance etc., has two groups of precision low-noise operational amplifier in LM747, and maximum operating frequency, up to 1MHz, is used in the circuit of this accurate low-noise operational amplifier and can be formed good waveform。Wide pulse signal is through LM747 low pass filter its mean direct component exportable, then with sampling shaping circuit, low-pass filter signal is carried out shaping, makes output signal can provide the sampling desired signal of decision circuit。

(4) sampling decision circuit invention

Sampling decision circuit adopts the double D trigger CD4013 that band is to be resetted to invent, and after the DC component signal of low-pass filter circuit output adjudicates shaping then through 4013, has both obtained demodulation original figure baseband signal。

Installation and debugging

(1) process of circuit is debugged

A.FSK signal, after amplifier UA741 and band Schmidt trigger CD40106 carries out shaping, obtains as fsk signal is converted to the square wave with modulation signal。

B. obtaining positive and negative spike after bistable multivibrator CD4098 circuit differential shaping, the number of spike reflects the number of times of FSK zero crossing, and negative pulse is swung to into positive pulse, embodies the correct number of times of zero crossing。Differential shaping circuit CD4098 is the key in the invention of this circuit and difficult point。

C. obtain certain altitude and the square wave of certain pulsewidth through pulse shaper, the dutycycle of square wave is adjustable by RC circuit, and the mean direct component of signal is directly proportional to pulse recurrence frequency, is namely directly proportional to the carrier frequency of input signal。This is a step important in circuit debugging process, and in zero passage detection, the signal difference of two carrier frequency frequency differences and 2K and 4K is more big, it is shown that, mean direct component is then more big, and interference free performance is also more good, but shared frequency band is also more wide。

D. the square wave that accurate low-noise operational amplifier LM747 circuit treats signal processed is filtered, and low pass filter exports its pulse direct current component。

E. last by after double D trigger CD4013 judgement shaping, namely obtain demodulation original figure baseband signal。Cross zero detecting method debugging process oscillogram。

Claims (9)

1. adopt the invention of unit element circuit, the actual training device of combination of wireless telecommunication is carried out again with connection wire, such advantage is functional module elements, student deepens the study to high-frequency circuit and understanding by unit circuit, and signal is also easy to test and regulates, but when being combined into corresponding functional module, more because connecting wire, comparatively mixed and disorderly to student's sensation on the one hand, there is also certain interference simultaneously, and radio communication is comparatively sensitive to interference signal reflection；

Adopt the integrated corresponding functional module of element circuit, each module is relatively independent in system, and the connection wire between module is less, is the transmission relation between final stage, element circuit in functional module is not had and disturbs, make experimental system more succinct simultaneously yet；The advantage that invention absorbs invention one on the other hand, utilize short-circuiting terminal that the element circuit in functional module is separated, so namely element circuit can be tested and invent, it is also possible to form specific wireless transmission communication system by relatively independent functional module；

FM radiating circuit invention invention demonstration and selection。

2. invention one: adopt monolithic FM transmission integrated circuit MC2833 and interlock circuit composition；It may make up the power amplifier launching high-frequency signal；But the resonant tank related to due to this chip is more, not easily tracking, thus frequency is wayward, causes jitter, easy treadmill, it is achieved comparatively difficulty。

3. invention two: adopt integrated chip BA1404 and interlock circuit to constitute；It is mainly by audio preamplifier, stereo modulator, FM manipulator and radio frequency amplifier composition；Internal reference voltage is utilized to change the capacitance of varactor, it may be achieved the adjustment of tranmitting frequency。

4. typical case's frequency modulation frequency range is 75-108MHz；

In sum, selection invention two of the present invention, namely utilize integrated chip BA1404 to realize FM radiating circuit；

FM receives radiating circuit invention invention demonstration and selects

Adopt the chip MC3362 that MOTOROLA company of the U.S. produces；This chip is that monolithic narrow-band FM receives circuit, is mainly used in speech communication and the wireless receiver of data transmission；The circuit such as oscillating circuit, mixting circuit, limiting amplifier, integral discriminator, field intensity instruction driving and carrier frequency detecting circuit are comprised in MC3362 sheet；There is low suppling voltage, low-power consumption, sensitivity high；But this circuit is relatively used for FM radio receiver, in the frequency range required, carry out debugging relative difficulty；

Adopt integrated chip CXA1238S；This chip internal comprises the links such as the preposition amplification of FM, stereo demodulation amplification, the amplification of FM intermediate frequency and frequency discrimination, especially have employed Phase Lock Technique in chip, thus has central stabilizer, tunes the advantages such as simple, strong interference immunity, circuit stability；

System is made up of nine high frequency real training circuit modules, respectively by transistor oscillating circuit, and AM transmitter circuitry, AM receiver circuit, FM transmitter circuitry, FM receiver circuit, FSK modulation circuit, Fsk demodulator, CPLD frequency counter circuit, system power supply circuit module etc. forms；

Modular circuit is invented

LC and the invention of transistor oscillating circuit

Element circuit is invented

The output of LC and transistor oscillating circuit is the carrier signal source of transmitter, it is desirable to its vibration is sufficiently stable；Generally using crystal oscillating circuit, wherein Q-value is up to tens thousand of, and its frequency stability is up to 10-5～10-6；Crystal oscillator JT and C1, C2, C3, VT1 constitute Colpitts oscillation circuit, and frequency of oscillation is 3.579MHz；R1, R2, R3 in circuit determines the quiescent point of transistor, and wherein R1 can adjust；When quiescent point is arranged, first set collector current ICQ, general ICQ and take 0.5～4mA, ICQ too conference and cause output waveform distortion, produce higher hamonic wave；If transistor β=60, ICQ=2mA, UEQ=(1/2 ~ 1/3) Ucc, then can calculate R1, R2, R3；Shown installation circuit, UBQ=8.3V, UEQ=7.7V in debugging；

Installation and debugging

During debugging crystal oscillator, should first disconnect crystal oscillator, make agitator nonoscillatory, then survey each step voltage of audion with circuit tester；UEQ should meet

UEQ/(R2+R3) ≈ ICQ=2mA

If being unsatisfactory for, then adjustable R1 value；The quiescent point of audion is debugged after correctly, then connect crystal oscillator, measure the frequency of oscillation of agitator and the amplitude of output voltage；Want selecting properly test point during measurement, make the input impedance output impedance much larger than circuit test access point of instrument；Also should meet load resistance RL, RL at outfan should be equal with the equivalent input impedance of next stage circuit；If the input impedance of instrument is higher, then optional A point is measured；If the input impedance of instrument is relatively low, then B point should being selected to measure, the value at this moment coupling electric capacity Co is about 20pF；

AM transmitter circuitry is invented。

5. invention thinking

Single-frequency point refers to the Frequency point that carrier frequency is fixed value launched and receive, and so in the factor launched with do not need consideration to cause amplifier performance different because wave band is different when receiving, simplifies invention difficulty；Either simplex refers to that transmitter receiver cannot receive when launching, and cannot launch when receiving, and namely once can only carry out a kind of operation, or launch, or receive；So, a transmitter receiver is only comparable to the combination of a transmitter and a receiver, controls the conversion launched with receive with a switch；For the simplicity invented, general transmitter receiver adopts amplitude modulation to launch and receives；

Operation principle and composition frame

Its operation principle is: the first local oscillation produces the intermediate-freuqncy signal of a fixed frequency, and its output is delivered in manipulator；Speech amplifying circuit amplifies the signal from microphone, and its output is also delivered in manipulator；Manipulator output is amplitude modulated intermediate-freuqncy signal, and this signal is mixed with the second local oscillation signal after intermediate frequency amplifier amplifies；Second local oscillator is the signal source of a changeable frequency, generally selects the second local frequency?O2 is first vibration frequency?O1 and transmitting carrier frequency?O1 sum；Frequency mixer exports through bandpass or low pass filter, makes output carrier frequency?C=?O2-?O1；CF signal is carried out the power amplification power to required transmitting by power amplifier level；

The key technical indexes

(1) operating frequency range

The operating frequency of some frequency AM transmitter is 3.579MHz；

(2) transmitting power

Generally referring to the power that transmitter is transported on antenna, only when the wavelength X of the length of antenna Yu tranmitting frequency can be compared, carrier wave could be launched by antenna effectively；Wavelength X and frequency?Relation be:

λ=с/?

In formula, с is propagation velocity of electromagnetic wave, с=3 × 108m/s；

If the sensitivity S A=2 μ V of receiver, then the relation of communication distance S and transmitting power PA is such as shown in table 1-1；

The relation of transmitting power PA and communication distance S

PA/mV50100200300400500600700

S/km2.843.384.024.454.825.085.275.50

The transmitting power Po of this circuit >=150mW；

(3) modulation

Modulation is the coefficient that modulation signal controls carrier voltage amplitude variations, and its span is 0～1, generally in per cent, namely ranges for 0%～100%；The characteristic of non-linear distortion (envelope distortion) manipulator can not be followed modulation voltage linear change and be caused the non-linear distortion that envelope distortion is AM transmitter of modulated wave, generally requires less than 10%；Linear distortion keeps modulation voltage amplitude constant, and the modulation depth characteristic variations that change modulating frequency causes is called linear distortion；This circuit modulation degree be 50%；

(4) noise level

Noise level refers to when not modulating signal, noise the modulation depth produced and signal modulation depth ratio time maximum；The noise level of broadcast transmitter requires less than 0.1%, and the noise level of general communication equipment requires less than 1%；

(5) aggregate efficiency

The ratio of the general power P ' c that the general power PA that transmitter is launched consumes with it is called the aggregate efficiency η A of transmitter, namely

η A=PA/P ' c；Aggregate efficiency η >=40% of this circuit

Element circuit is invented

(1) modulation circuit

According to the meaning of the question and given main devices, selected analog multiplier MC1496 constitutes modulation circuit；

If u is Ω=U Ω mcos Ω t=U Ω mcos (2 π?Ω t)

Carrier wave uc=Ucmcos Ω t=Ucmcos (2 π?Ct)

It is multiplied with carrier wave uc plus direct current UDC:

uAM=UM(1+MacosΩt)cosωct

In formula, index of modulation Ma=U Ω M/UDC≤1, otherwise can produce excessive amplitude modulation；

The each pin function of MC1496 is as follows:

1), SIG+ signal input anode 2), GADJ gain-adjusted end

3), GADJ gain-adjusted end 4), SIG-signal input negative terminal

5), BIAS offset side 6), OUT+ positive current outfan

7), NC sky foot 8), CAR+ carrier signal input anode

9), NC sky foot 10), CAR-carrier signal input negative terminal

11), NC sky foot 12), OUT-negative current outfan

13), NC sky foot 14), V-negative supply

When arranging the quiescent biasing of MC1496, the audion within multiplier should be made all to be operated in magnifying state, and make quiescent point be in the midpoint of dc load line as far as possible；The static bias voltage of each pin when debugging；

Pin 12345681012

Voltage-6-6.5-6.5-6-10.4+6.9+0.5+0.5+6.9

(2) speech amplifying circuit

According to given main devices, uA741 is integrated operational amplifier, it is possible to it, low frequency voice is amplified；Its output voltage is:

(3) buffer circuit

The input impedance of emitter-follower is big, output impedance is little, can significantly improve the performance of circuit, and therefore, conventional emitter-follower makees buffer circuit；During invention emitter-follower, mainly consider the matching problem of input impedance and output impedance and front stage；

(4) power amplification circuit

The power amplifier that wide-band transformer does coupling circuit is utilized to be called wideband power amplifer；The high frequency transformer of the useful high frequency magnetic core coiling of common wide-band transformer and transmission transformer；Wideband power amplifer does not need tuned vibration loop, can obtain linear amplification, but efficiency eta is relatively low in very wide frequency range, and general only have about 20%；It is usually used as the intergrade of transmitter, to provide bigger exciting power；

Frequency-selective network is utilized to be called resonance amplifier as the power amplifier of load circuit, the scope according to amplifier current conduction angle, it is possible to be divided into Class A, Class B, Class C and class D constant power amplifier；Current lead-through angle θ is more little, and the efficiency of amplifier is more high；Typically by the class C power amplifier final stage as transmitter, to obtain bigger output and higher efficiency；

For the high frequency power amplifier circuit that is made up of two stage power amplifier；Wherein transistor VT1 is buffer stage, and transistor VT2 and high frequency transformer Tr1 forms wideband power amplifer, and transistor VT3 also frequency-selective network L3, C6 forms Class C tuned power amplifier；

1. wideband power amplifer

The determination of quiescent point Q:

UBQ=UCCR6/ (R5+R6)

UEQ=UBQ-0.7=ICQ(R7+R8)

UCEO=UCC-UEQ=UCC-ICQ(R7+R8)

Wideband power amplifer colelctor electrode output PC is:

PC=PH/ηT=1/2UCMICM

In formula, PH is the actual power in output loading；η T is transformator efficiency of transmission, is generally 0.75～0.85；

UCM=UCC-ICQR8-UCES

In formula, UCES is saturation voltage drop, is about 1V；

ICM≈ICQ

Transformer turn ratio K is:

K=[(η TR'H)/RH] 1/2

In formula, RH is that VT2 exports impedance；R'H is the input impedance of understage transistors VT3；

2. class C power amplifier

The base bias voltage of Class C power amplifier is that the DC component IE0 the utilizing emission current pressure drop produced on emitter resistance R10 provides, therefore is called autobias circuit；

Colelctor electrode fundamental voltage amplitude is:

UC1m=IC1m/RP

In formula, IC1m is colelctor electrode fundamental current amplitude；RP is collector load impedance；Colelctor electrode output is:

Pc=UC1mIC1m/2

The dc power of direct-current power supply is: in PD=UCCIC0 formula, and IC0 is the DC component of colelctor electrode pulse；

3. the coiling of high frequency transformer；

The magnetic core of high frequency transformer should adopt nickel zinc (NXO) ferrite, and can not use silicon sheet core, because stalloy iron loss when high-frequency work is excessive；When making high frequency transformer magnetic core with NXO 100 circular ferrite, operating frequency is up to tens megahertzs；After determining core material, its inductance value can be determined by the number of turn of L coil, and the number of turn is more many, and inductance value is more big；In order to reduce the impact of coil leakage inductance and distribution capacity, the number of turn should be as far as possible less, and turn-to-turn distance should be big as far as possible；

Installation and debugging

Circuit debugging first should adjust quiescent point at different levels respectively, then adjusts output signal step by step from prime level backward；

The test of manipulator

When surveying modulator circuit quiescent point, local oscillation signal UO=0 should be made, modulate signal U Ω=0；First survey the voltage U5 on MC1496 the 5th foot, adjust the value of R5, make | U5 |/R5=I0；Then measuring each static work voltage, its value should be worth roughly the same with invention；Add local oscillator voltage Uo=100mV, make modulation voltage U Ω=0, regulate RP3 and make MC1496 output signal be minima, then make U Ω=100mV, at this moment the output waveform recorded should be the repressed double-sideband signal waveform of carrier wave, then regulates the RP3 amplitude-modulated wave making output waveform be Ma=50%；

The block diagram of superhet crystal radio circuit and the oscillogram of signal at different levels；The radio that invention currently uses is essentially all superheterodyne radio set, is characterized in: former high frequency carrier through frequency changer circuit frequency conversion, to be transformed to the intermediate-freuqncy signal that unified frequency is relatively low by the radio signals that radio receives；Then amplify then through intermediate frequency, demodulation is reduced into acoustical signal；Superheterodyne radio set have highly sensitive, selectivity good, steady operation and other merits；

The key technical indexes

(1) operating frequency range

The operating frequency of AM transmitter is 3.579MHz；

(2) sensitivity

Receiver outfan is when meeting specified output and certain output signal-to-noise ratio, and the minimum signal voltage needed for receiver inlet is called the sensitivity of receiver；The sensitivity of AM receiver is generally 5～50 μ V；

(3) selectivity

Receiver selects useful signal from the signal (including interference signal) of the many different frequencies acted on receiver antenna, suppressing the ability of near by frequency signal disturbing to be called selectivity, generally near by frequency damping capacity is represented by three dB bandwidth and receiver with receiver reception signal simultaneously；Generally require that three dB bandwidth is not less than 6～9kHz, 40dB bandwidth and is not more than 20～30kHz；

(5) intermediate frequency rejection ratio

Receiver suppresses the ability of intermediate frequency interference to be called intermediate frequency rejection ratio；Representing intermediate frequency rejection ratio typically by the ratio that frequency input signal is sensitivity S IF and receiving sensitivity S during the machine intermediate frequency, in units of dB, namely intermediate frequency rejection ratio=20lg (SIF/S) dB decibels is more big, illustrates that anti-intermediate frequency interference performance is more strong；Generally require that intermediate frequency rejection ratio is more than 60dB；

(6) image-frequency rejection ratio

The rejection ability that receiver disturbs for image frequency (image frequency) is called image-frequency rejection ratio；Image frequency=?S ± 2?I

In formula,?S is signal frequency；?1 is IF-FRE；Local frequency being higher than to the receiver of signal frequency, its image frequency is?S+2?I；For the local frequency receiver lower than signal frequency, its image frequency is?S-2?I；Image-frequency rejection ratio is represented typically by the ratio that frequency input signal is sensitivity S IM and receiving sensitivity S during image frequency, generally in units of dB, i.e. image-frequency rejection ratio=20lg (SIM/S) dB

Decibels is more big, illustrates that the ability of anti-image interference is more strong；Usually require that image-frequency rejection ratio is more than 60dB；

(7) AGC control

Receiver utilizes its gain of carrier Control received in signal to ensure that the constant ability of output signal level is called AGC control；During measurement, generally making receiver input signal start to step up from certain setting, until receiver exporting change to certain setting (such as 3dB), the decibels that now incoming signal level increases is the AGC control of receiver；

(8) output

Receiver maximum non-distortion power in output loading is called output；

Element circuit is invented

(1) input circuit

Sensed the high-frequency signal obtained by magnetic antenna, be actually high-frequency carrier signal and selected to obtain being intended to receive radio signals through LC resonant tank；(for making radio obtain higher selectivity, sensitivity, suitable L1 and L2 turn ratio should be selected；Now the aerial coil of dress is ready-made has invented, it is desirable to student notes as far as possible, coil is not broken, and otherwise removes coil and reduces the number of turns and affects turn ratio)；

(2) frequency changer circuit

The high-frequency signal sent here by input circuit is amplitude-modulated wave, and the local oscillation frequency signal that local oscillation produces is persistent wave, obtains 465KHZ intermediate-freuqncy signal through frequency-selecting after mixing；Therefore converter stage Main Function is the intermediate-freuqncy signal that the high-frequency signal of amplitude modulation becomes amplitude modulation；It is only that carrier frequency changes before and after conversion, and signal envelope is constant；General vibration and the mixer action completing this machine with a frequency-converter tube；To mixing, it is desirable to be operated in inelastic region, electric current can not be too big, and otherwise conversion gain declines, but to local oscillator, more greatly, conversion gain height is easily starting of oscillation again for electric current, and cell voltage decline is not easily left alone without help shakes；But vibration can not be too strong, and wave distortion otherwise can be caused to hear " coughing up ", " coughing up " sound, and gain declines on the contrary, and generally selecting electric current is 0.4～0.6mA；

(3) intermediate frequency amplifies

In put the quality of level radio sensitivity, selectivity etc. had decisive influence；In to put level work frequency be 465KHZ, do load with LC resonant tank in parallel, therefore only when signal frequency is 465KHZ, shunt-resonant circuit voltage is maximum, therefore improves complete machine selectivity；Radio adopts in one-level sometimes puts (be generally in two grades and put) Single-tuned intermediate frequency amplifier, and selectivity and sensitivity are not necessarily very good, but return loss is little, easy to adjust, therefore Pocket Computer this circuit widely used；

(4) detector stage

Intermediate-freuqncy signal is still amplitude-modulated signal, through detector stage (by diode or triode detection), takes out audio signal from amplitude-modulated wave；If what select is audion, utilizing one of them PN junction to play big signal demodulator effect under non-linear working state, this pipe also carries out reflex low-frequency current amplification simultaneously；

(5) low put and power amplification

Audio signal after detection is delivered to low discharging grade and is carried out audio frequency amplification, then passes through input tranformer and delivers to push-pull power amplifier level and carry out power amplification, and output signal promotes speaker to send sound；The pipe work of push-pull power amplifier circuit is in Class B state；Ending when no signal, second engineman stream work when having a signal, therefore efficiency is high, but produces distortion at characteristic curve sweep when Class B is operated in small-signal；Therefore this machine circuit ground level when no signal also has certain bias, so as to be operated in class AB state, such efficiency is high, and output is big, and power saving；Subparameter is consistent by all means in requirement two；Wish when assembling selected；All have one to damage by all means, it is necessary to pairing choosing pipe；Notice during welding that two pipes weld, as rosin joint one is managed, cause a pipe job to produce serious distortion, and volume is greatly reduced；

Installation and debugging。

6.(1) element introduction

The kind of the variable capacitance used by radio is much used herein is that difference holds duplex；Vibration connection is 68pF；Antenna connection is the medium-sized doubly-linked of 140PF；The one end being marked with " A " at dual capacitor is antenna connection, and the one end indicating " O " is vibration connection；Centre is that what to indicate " G " is earth terminal；The bar magnet of magnetic antenna is of a size of 55X13X5mm；Winding and the number of turns of coil are shown in circuit theory；Coil is all with the high strength enamelled wire coiling of Φ 0.13；Medium wave oscillator coil B2(magnetic cap is black) model be LF10-l；The model of intermediate-frequency transformer is TF10-1 and TF10-2；All with resonant capacitor in these two intermediate-frequency transformers；Magnetic cap in first intermediate-frequency transformer B3 is white, and the magnetic cap in the second intermediate-frequency transformer B4 is green；

Audion is all NPN type silicon materials plastic packaging pipe, and wherein BG1, BG2, BG3 all select 3DG201；BG4 can be selected for 3DG201 or 9014；Their β value should between 150～200；The β value of frequency-converter tube should not be too big, is typically in about 60 times；BG6 and BG7 can with 9013；Their β value is not less than 100；Diode is 1N4148；Resistance is all 1/8W carbon film electricity resistance；Electric capacity C4, C7, C8 are electrolysis condenser；C3 is dacron terylene condenser；All the other are ceramic capacitor；

(2) circuit is installed

According to the experimental circuit that laboratory provides, whether the kind of the provided element in checking experiment room, model and quantity is correct；Owing to radio element is many, circuit is more complicated, therefore when assembling, generally wants the assembling of one-level one-level；Wireless sequence is precisely contrary with signal flow, namely assembling process should from power amplifier level, set low before being followed successively by put, letter wave scale, in put level, agc circuit, be finally converter stage and input circuit, such rank groups is equipped with the adjustment and the test that are beneficial to circuit；

(3) working direct current at different levels is adjusted

Millivoltmeter it is connected in series between colelctor electrode and DC source, select corresponding range, regulate biasing resistor Rb, (general with a fixed resistance go here and there again a upper potentiometer), make the numerical value that millivoltmeter indicates reach the operating current of regulation, then pull down this fixing resistance and potentiometer measures all-in resistance；Change the fixed resistance of corresponding resistance again；Even if this one-level regulates；Note:

A: when adjusting DC point, radio no signal should be kept to input；All screw in for this dual capacitor or all screw out；

B: also should survey operating current after changing the resistance of fixed resistance value again；Finally it is also noted that and two test points in printed circuit are connected；

(4) IF-FRE (in tune week) is adjusted

The method adjusting IF-FRE has instrument testing method and audition method etc. multiple；

Instrument testing method turns on radio, opens big volume potentiometer, by the wireless whole precession of doubly-linked variable condenser, avoids extraneous signal；Being regulated on 465kHz by the output frequency of HF signal generator, modulating frequency 1000Hz, modulation is adjusted on 30%；High-frequency signal (465kHz) after low frequency modulations couples electric capacity by 0.01～0.047 μ F, by wireless Base injection, regulates the output of signal generator so as to be gradually increased by little, can not hear with the sound in speaker and be as the criterion；Regulate by week in the third level, carry out forward step by step；With the magnetic cap of noninductive bakelite or screwdriver turn intermediate-frequency transformer, oscillograph or millivoltmeter is made to obtain maximum output；Said process should adjust several times repeatedly；If there is self-excitation, neutralizing capacitance and middle all transformators to be readjusted；The value of neutralizing capacitance is generally about 2pF；

(1) main feature of BA1404

A. adopting low-voltage, low-power consumption invention, voltage is between 1～3V, and representative value is 1.25V, maximum power dissipation 500mW, b. quiescent current is 3mA；

C. by stereo modulation, FM modulation, radio frequency amplifying circuit integrated on a single die；

D. required peripheral cell is few；

E. two channel separations are high, and representative value is 45dB；

F. input impedance is 540 Ω (fin=1kHz), and input gain is 37dB (Vin=0.5mV)；

G. typical radio-frequency output voltage is 600mV；

(2) pin function and chip introduction

BA1404 is mainly by audio preamplifier (AMP), stereo modulator (MPX), FM manipulator and radio frequency amplifier composition；

The audio frequency amplifier of stereo prestage respectively two sound channels；When input is for 0.5mV, gain is up to 37dB, and bandwidth is 19kHz；As inputted the composition that there is frequency in signal higher than 19kHz, then must adding a low pass filter at input, otherwise the separating degree of two sound channels can decline；

In stereo modulation group, the 38kHz signal of agitator output is in stereo modulation；Generally connect an adjustable resistance at 16,17 feet, to obtain the channel separation degree of the best；Stereo mix signal (MPX exports signal) and pilot tone export the modulation signal after signal (PILOTOUT) synthesizes and enter radio-frequency oscillators by 12 feet and carrier wave is carried out FM modulation, output radiofrequency signal after radio frequency amplifies, the representative value of radiofrequency signal is at about 600mV；

A reference voltage unit VREF is additionally provided inside BA1404；Inventor can utilize this voltage signal to change the capacitance of external varactor, then changes the frequency of oscillation of carrier wave；Therefore, as long as the partial pressure value controlling a resistance just can reach to change the purpose of tranmitting frequency, this is the invention that comparison is unique；

During invention it should be noted that following some:

(1) in order to make the frequency response of transmitter and FM receiver be mutually matched, need to adding preemphasis network at input, its time coefficient is 50 μ s；

(2) at 13,14 feet, when the stereo mix signal of stereo modulator output and pilot signal synthesize, it is possible to cause the separating degree of stereo channel to worsen, so must be noted that the value of 12,13,14 foot peripheral cells；

By to invention demonstration, have selected CXA1238M chip as low pressure amplitude modulation/f-m stereo sound reception integrated circuit, its internal amplitude-modulated portions includes and receives the repertoire to the output of detection audio frequency from antenna, frequency modulation part includes and receives the repertoire to stereo decoding, the output of left and right acoustic channels audio frequency from antenna, as long as external one piece of stereo audio power amplifier and a small amount of peripheral cell just can be assembled into a complete AM/FM stereo receiver。

7. operation principle and composition frame

Adopt integrated chip CXA1238S；This chip internal comprises the links such as the preposition amplification of FM, stereo demodulation amplification, the amplification of FM intermediate frequency and frequency discrimination, especially have employed Phase Lock Technique in chip, thus has central stabilizer, tunes the advantages such as simple, strong interference immunity, circuit stability；

From the FM signal that antenna receives, through 87～108 GHz bandpass filters (BPF), be added to the 18 feet outputs of IC, deliver to internal FM pre-amplification circuit, put through height, be mixed after demodulate the intermediate-freuqncy signal of 10.7 megahertzs, and exported by 16 feet；The 20 external FM high-frequency amplifying tuning loops of foot, 22 feet are FM local oscillator resonant tank；Equally, amplitude-modulated signal injects (19) foot after being tuned by antenna input circuit, and local oscillation signal injects 24 feet, and after mixing and the preposition amplification of AM, 465 kilo hertzs of intermediate-freuqncy signals also deliver to 16 foot outfans；The 24 external AM oscillator coils of foot；

The 16 external two-way frequency-selective networks of foot, 14 feet of 465 kilo hertzs of AM intermediate-freuqncy signal feed-in IC, through intermediate-frequency transformer T1, intermediate-frequenkcy ceramic filter B1, are selected in a road, are added in internal AM and put and detector stage；Another road FM intermediate-freuqncy signal is put and frequency-discriminating circuit in 10.7 megahertzs of ceramic filter B2, feed-in 13 foot FM；The 26 external FM ceramic discriminator B3 of foot, its mid frequency is 10.7 megahertzs, so can save the adjustment of frequency discrimination S curve, but its colour code (expression frequency departure) must be consistent with B2；

The 15 external range switches of foot, by the effect of the internal FM/AM DC converting circuit of IC, select duty；It is FM wave band when S1 disconnects, is AM wave band during s1 ground connection；12 feet are the outfan coordinating instruction drive circuit so that when reception signal is maximum, external LED 1 indicates the brightest；

Stereo composite signal (or monophonic signal) after detection, controlled voltage by being transformed into AGC/AFC after direct current amplifier amplification, filtering in IC, 10 feet export, feed back to 23 feet by R1, for connecing the equivalent capacity of varactor in controlling, to reach to revise the effect of local oscillator；Change the capacity of external capacitor C7。

8. phase discriminator 1, voltage-controlled oscillator (VCO) (VCO) and frequency divider composition phase-locked loop；VCO produces the oscillator signal of 76 kilo hertzs, becomes 38 kilo hertzs of stereo demodulation switching signals after two divided-frequency, delivers to demodulator amplifier；Then through two divided-frequency, and 19 kilohertz signal after phase shift 90 ° carry out phase bit comparison with 19 kilo hertzs of pilot signals in composite signal in phase discriminator 1, export an error voltage；After being filtered radio-frequency component by external low pass filter (between 29 feet and 1 foot), for controlling frequency of oscillation and the phase place of VCO, until loop-locking；The free oscillation frequency of VCO can be finely tuned by 27 foot outer meeting resistances, thus adjusting the catching range of TPS Tracking Pilot Signal；

The effect of phase discriminator 2 is to detect stereo/monophonic switch controlling signal；When after frequency dividing, 19 kilohertz signal are identical with the frequency of input pilot signal, when phase contrast is zero, output positive voltage is maximum, after low-pass filtered device filtering (2,3 foot external capacitor) and direct current amplify, open " stereo/monophonic " switch, and the 4 external stereo indication light diode (LED)s 2 of foot are lighted in driving；It addition, 4 feet can also be used to detection VCO frequency of oscillation；

The left and right sound channels signal of output is amplified in demodulation, respectively from 6 feet and 5 outputs, delivers to input 2 foot and 3 feet of ULN3782M double power amplifier circuit；ULN3782M adopts 8 foot circular row straight cutting encapsulation, and volume is little, and peripheral cell is few, working power voltage scope 2～9 volts, and when VCC=6V, output is 430 Europe, milliwatt/8 and 240 Europe, milliwatt/16;When VCC=4.5V, output is 220 Europe, milliwatt/8 and 125 Europe, milliwatt/16；RP1-2 is stereo doubly-linked potentiometer, controls the volume of left and right sound channels, and XS is stereo jack, can be used for external stereophone or with to small-size sound box；

XA1238 is the radio integrated circuit of function admirable, inside has the height of AM, FM to put, is mixed, in put, detection, the function such as frequency discrimination and FM stereo decoding, automatic frequency control circuit, compared with the similar radio reception IC of other companies, sense of hearing also feels warm comfortable。

9. this FM receiver adopts earphone cord to make antenna, the high-frequency signal sensed by earphone cord coupled to band filter BPF through C21, BPF filters out the high-frequency signal beyond 88-108MHz, fm broadcast signal then delivers to the base stage of V1, sent into antenna input the 18th foot of IC1 by C20 after V1 amplifies, and generation frequency is 10.7MHz intermediate-freuqncy signal after being mixed with integrated internal local oscillation signal, this intermediate-freuqncy signal is exported by 16 feet, in order to improve sensitivity and the selectivity of receiver, this circuit is also provided with the gain that one-level is made up of V2 and peripheral cell be 18db pre-in put, the intermediate-freuqncy signal of 16 foot outputs delivers to V2 through C23, exported by its colelctor electrode after V2 amplifies and filter out 10.7MHz intermediate-freuqncy signal through intermediate frequency discriminator CF2, 13 feet of IC1 are sent into by R7, then L is recalled by integrated Interior Solutions, R two-way audio signal is respectively by 5, 6 foot outputs, earphone jack P is delivered to after being done further power amplification by IC2 after volume potentiometer W, and promote earphone to send sound；

FSK modulation circuit is invented

FSK principle and signal produce frame

(1) FSK principle

Frequency shift keying (FSK) is to utilize Digital Signals carrier frequency to transmit information；Available digital baseband signal goes to control an analog switching circuit, for instance " 1 " code transmits frequency f1, and " 0 " code transmits frequency f2；Making its output frequency is alternate for f1 and f2 Sine Modulated waveform；

Element circuit is invented

Invented the modulation circuit of FSK by the principle of fsk signal waveform and FSK, circuit is made up of wave generator circuit, frequency dividing circuit, waveform translation circuit, analog switching circuit etc.；

(1) wave generator circuit

The crystal oscillating circuit that wave generator circuit is made up of 4096 reversers and 4.096MHZ produces the sine wave signal of 4.096MHZ；

(2) frequency dividing circuit

Frequency dividing circuit adopts the CD4042 digital frequency divider of two panels 14 frequency dividing to divide；Because wave generator circuit produces the sine wave signal of 4.096Mhz, and by 2KHz, fsk signal represents that signal 0 and 4KHz represent what signal 1 formed respectively, so original signal to be divided, invention have employed 7 grade of 128 frequency dividing CD4042 chip of two panels to form frequency dividing circuit；Thus the signal waveform of 2KHz, 4KHz, the 500Hz needed for obtaining module；

(3) waveform translation circuit

Waveform varying circuit is constituted waveform conversion by amplifier UA701 and peripheral resistance capacitance, the square-wave signal that frequency dividing circuit exports is transformed to sine wave signal, meets the requirement of the signal of modular circuit；Its principle is that square-wave signal is carried out shaping by the resistance capacitance composition charge-discharge circuit that make use of amplifier peripheral；；By formula:

=RC and=1/F determines R, C parameter value in circuit；

(4) analog switching circuit

Analog switching circuit adopts the CD4052 chip of Liang Zu tetra-tunnel input, and two-way carrier frequency produces fsk signal after the analog switch 4052 that digital baseband signal controls；

Fsk demodulator is invented

FSK demodulation principle and signal produce frame

(1) FSK demodulation principle

The demodulation of fsk signal is divided into coherent demodulation and non-coherent demodulation；Non-coherent demodulation is divided into frequency-discrimination method, zero passage detection method, differentiation etc.；

When adopting zero passage detection method, fsk signal, through amplifying amplitude limiter circuit, obtains pulse signal；After after differential shaping, obtain spike signal, its pulse number represents the number of times of fsk signal zero crossing；Obtain certain altitude and the square wave of certain pulsewidth through pulse shaper, the dutycycle of square wave is adjustable by RC circuit, and the mean direct component of signal is directly proportional to pulse recurrence frequency, is namely directly proportional to the carrier frequency of input signal；Low-pass filtered device follower exports its mean direct component, after judgement shaping, has both obtained demodulation original figure baseband signal；

In zero passage detection, two carrier frequency frequency differences are more big, and mean direct component is then more big, and interference free performance is also more good, but shared frequency band is also more wide；The selection principle of the cut-off frequency fc of low pass filter is。