SU1432415A1 - Spectrum analyser - Google Patents

Abstract

The invention relates to a radio metering technique and is intended for the spectral analysis of periodic electrical signals, the measurement of amplitude-frequency characteristics (AFC) and phase-frequency characteristics (PFC) of two-port networks. The purpose of the invention is to enhance the functionality of a spectrum analyzer (AC) by measuring phase shifts at a fixed frequency. The AC includes a frequency converter, a detector, a control and processing unit, an indicator, a local oscillator, a phase detector, a sweep generator, a frequency converter 8, and a reference oscillator. The control and processing unit includes a connector 10, a switch II connected in series, an analog-to-digital converter 12, a random access memory 13, a digital-to-analog converter 14, a synchronization unit 15, an operational amplifier 16, switches 17.18, and connectors 19,20,21,22. The use of a phase detector and a control and processing unit, as well as their connections, make it possible to expand the functionality of the instrument. The introduction of a phase detector into the AC, which measures phase shifts at a fixed frequency with high accuracy, makes it possible to measure the phase response of two-port networks in a wide frequency range (4-5 decades) S SL oo 4 SL

Description

19 ° with zetf rotor 7 unwrapping f

The invention relates to radio metering technology and is intended for spectral analysis of periodic electrical signals, measurement of amplitude-frequency ;: characteristics (AFC) and phase-frequency characteristics (PFH) of four axes.

The purpose of the invention is to expand the functionality of a spectrum analyzer (AC) by measuring phase shifts at ph x xirovannogo frequency,

FIG. I shows the functional scheme of the proposed AS; in fig. 2 is a block diagram of the y-block;

The spectrum analyzer contains a frequency converter 1, a detector 2, a control and processing unit 3 ,. indie-- kator A, local oscillator 5, phase detection 6 |, generator 7 sweepj of pre 6; frequency generator 8 and reference generator 9,

The AC input is connected to the first input of the converter 1, and the output is connected to the output of the converter 8 “The second inputs of the converters 1 and 8 are connected to the outputs of the local oscillator 5“ whose input is connected to the first output of the sweep generator 7. To the converter code 1 connect: detector 2 and phase detector 6 detector, the second input of which is connected to the output of the reference

„-

Oscillator 9 and the first - input of the transducer 8, Outputs of the detector 2 of the phase detector 6 and the generator 7 are connected to the inputs of the block 3. whose code is connected to the input of the indicator 4

The control and processing unit 3 contains a connector O, successively connected switch 1, analog-digital converter (ADC) 2 "random access memory (RAM) I3j cis analogue converter (JAII) 14, block 15. Synchronization, operational amplifier (OA) 165 switches 17 and 18 and a split; 19-22,

The spectrum analyzer injects three modes of operation :, spectral analysis of electrical signals, measurement of the frequency response of a quadrupole, and measurement of the phase response of a quadrupole,

The first mode of operation, the spectral analysis of electrical signals occurs when the switches i 7 and 18 of the control and processing unit are turned on to the position T ,, Signals in

operating frequency range is fed to the input of the converter 1, containing input filters, mixers, amplifiers and F1-1. Tsh. In the converter 1, the signal with the frequency COg, j is converted into a signal with a fixed IF Sopets in accordance with the expression

, - 03 g

SE

in

where the signal frequency of the local oscillator is 5.,

The IF signal goes to detector 2, from the output of which the video signal goes to block 3 and then to the vertical deflection plates of the indicator 4.

The second mode of operation is the measurement of the rehpo, g, Tosnika circuit when KONfMyTators 17 and 18 (Fig. 2) are turned on to position I using the SG AC, consisting of the reference generator 9 and the converter 8, to which the secondary oscillator 5 is connected.

The reference oscillator 9 produces a signal of the frequency Od.. The converter 8 converts the signal of the CJ frequency into a signal of the frequency by ra

Qer in

according to you

WITH

og

(2)

Provided compliance with (1)

ITO frequency W ,. O pm

(2)

/ the assertion C0ff с е, х is true, i.e. The frequency of the SG signal is equal to the frequency of the speaker setting. The output level of the SG signal is stabilized in the frequency range of the AC. When measuring the frequency response of a quadrupole, the quadrupole being investigated is switched on between the SG output and the AC input. The frequency response to (03) quadrupole at frequency 03 is determined as follows

Cj) / Uj, ((O; (3:

where and

Up, silt.

iSK

the amplitude of the signal transmitted through the four-by-about-L10 with the input of the AC; .MP, l g--: t beats and the signal of the SG and the input of the four-regiment. -: th amplitude of sigil;; -, i dkkl-chone frequencies, spr

143

The third mode of operation of the AC - measurement of the phase response of the quadrupole is carried out when the switch 1 7 (FIG. 2) is turned on in the IT position. The remaining switches AU are placed in a certain position depending on the mode of operation of the AU npti measuring the frequency response.

The measurement of the phase response tf (co) of the quadrupole occurs in two stages: the measurement of the frequency response of the SG and the path of the AC and the measurement results are stored in the memory of the RAM 13 (thus, the calibration of the frequency response of the AC and SG is performed), the measurement of the joint frequency response of the four-pole, SG and tract AC, from the measurement result is subtracted by the phase response of the SG and tract ACJ recorded in the RAM, and the result of the subtraction, i.e. The frequency response of the quadrupole is indicated by the AC indicator.

Thus, at the inputs of the phase detector, when measuring the phase response of the SG and the AS path, signals are given

-

U (t}, t + tpo, + M pr,

lUj, (t) - cos (+4) 0).

Phase detector generates signal if | proportional to the phase difference of the input signals

B, ggr + right

where is the phase incursion into the converter,

H prb phase advance into the Converter 8,

In this case, the phase detector signal characterizes the common phase response of the SG and AC, which is stored in the RAM of the control and processing unit 3.

When measuring the phase response of a quadrupole, when it is turned on between the SG output and the AC input, the signal at the output of the converter can be represented as E

and (t) cos (O opt + tfor 4 np,

+ tf

prv

Cf (Q ,,),

where (J () is the phase response value of the quadrupole at frequency o)

.

Phase detector at the same time produces a signal

f A

 SG.RL Rrr8 - (Osg). (eight)

. five

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Wed - Yuaty 13 ob-15 ta ta 20

go

- 25

6)

35

ooh paanioode becoming

40

45

7)

50

heh

55

a8)

five

The signal and is fed to the input of the control unit 3 and processing, where from it. the subtraction of the signal characterizing the joint phase response, the AU and the SG occurs. Differential signal

and - - u, -c (c.v)

comes from control and handling unit 3 on the vertical deflecting plates of the indicator 4.

When the local oscillator 5 is tuned according to the frequency carried out by the sweep generator 7, the phase response frequency of the quadrupole is measured in the frequency range, and the function cf (co) - frequency response of the quadruple is displayed on the AC indicator screen.

The control and processing unit 3 in the measurement mode of the frequency response operates as follows.

When calibrating the phase response of the AC switch 11 is included in position II, which ensures the recording of the frequency response in the RAM memory. The switch 18, the switching sawtooth generator signal 7, is also included in position II and the signal

7 scan input

19 (FIG. 2) does not pass. On the indicator 40 i.e. indicator is off. The generator 7 generates a sawtooth signal that re-tunes the local oscillator 5 in frequency in a given range.

At the beginning of the sweep, the generator 7 generates a signal arriving at the connector 19 and the synchronization unit 5, whose pulses trigger the ADC 12, as a result of which it produces 256 samples of its input signal, which in binary code arrive at the input of the RAM 13.

Thus, during the sweep time in the PF calibration mode, 256 values are stored in the RAM 13 memory.

After a single frequency scan and the recording of measurement results in the RAM, the calibration process of the phase response of the SG and AC is considered complete.

At the second stage of measuring the phase response, when the quadrupole is switched on between the SG output and the AU input, the switches 11 and 18 (Fig. 2) are set to position I.

In this case, the phase detector 6 generates a signal defined by expression (7). This signal is fed to the connector 10 of the control unit 3 and

five

processing and through the switch 11 to the first input of the OS 16, the second input of which receives a signal from the DAC 14 connected to the RAM 13,

From the output of RAM I 3 sn: tatts data on the phase response of the AU and SG, presented in binary code, and sent to the IDP 14, which converts this data into an analog signal received on the second (inverse) input of the SU 16, at the output which forms a 1 s differential signal, representing an OG1F; a phase response quadrupole.

The signal enters the vertically deflecting plates of the indicator 4 The signal of the sweep generator 7 through the connector 19 and the switch 18 enters the horizontally deflecting plates of the indicator 4 In this case, on the screen of the indicator 4, the phase response of the quadrupole is indicated.

The use of a phase detector and a control and processing unit, as well as their connections, favorably casts the proposed speaker from the well-known one, since it makes it possible to expand the functionality of the device, namely the introduction of a phase detector to the speaker, measuring phase shifts at a fixed frequency with high accuracy , allows to measure the phase response of four-pole in a wide frequency range (4-5) decades with the same accuracy

156

FORUMU 3 and 3 ABOUT THIS

Spectrum analyzer, with () holder and (the first frequency converter, the first input of which is connected to the input of the quadrupole under study, the amplitude detector, the input of which is connected to generator, the output of which is connected to the first input of the second frequency converter, the local oscillator, the first and the second outputs of which are connected to the second inputs of the first and second converters respectively oy, a sweep generator, the first code of which is connected to the input of the local oscillator, as well as an indicator that, in order to extend its functionality, by measuring phase shifts at a fixed frequency, a phase detector and a control and processing unit are introduced, the first and second inputs of the phase detector are connected to the outputs of the first one, the frequency converter, and the reference generator, and the outputs of the amplitude detector, the phase detector and the sweep generator are connected It is connected to the first, second and third inputs of the control and processing unit, with its output connected to the input of the indicator.

four

five

-four

FIG. 7

Claims (1)

For r m u lz and z o b A spectrum analyzer, a first frequency converter, the first input of which is connected to the input of the four-terminal under investigation, an amplitude detector, the input of which is connected to the output of the first four-terminal converter, a second frequency converter, the output of which is connected to the input of the four-terminal under investigation, reference generator, the output of which is connected to the first input of the second frequency converter, a local oscillator, the first and second outputs of which are connected to the second inputs of the first and second converter, respectively frequency, a sweep generator, the first output of which is connected to the input of the local oscillator, as well as an indicator, which, in order to expand functionality by measuring phase shifts at a fixed frequency, a phase detector and a control and processing unit are introduced into it, moreover, the first and second inputs of the phase detector are connected to the outputs of the first, the frequency converter, and the reference generator, respectively, and the outputs of the amplitude detector, phase detector and. The scan generators are connected, respectively, to the first, second, and third inputs of the control and processing unit, with their output connected to the indicator input.