US2359551A - Carrier wave frequency converter - Google Patents

Description

Oct- 3, 1944- H. B. FANCHER CARRIER WAVE FREQUENCY CONVERTER Filed June 29, 1942 Inventor Henry B. Fancher, b9 fa/W51@ His Attorney.

Patented Oct. 3, 1944 CARRIER WAVE FREQUENCY CONVERTER Henry B. Faucher, Scotia, N. Y., assigner to General Electric Company, a corporation of New York Application June 29, 1942, Serial No. 448,994

2 Claims.

My invention relates to apparatus for converting the frequency of -a modulated carrier wave to a different frequency, and it has for one of its objects to provide new and improved apparatus for effecting such conversion directly, without demodulating the carrier wave to reproduce the signal as an intermediate step, and in which the final frequency of the carrier wave is controlled, with a high degree of precision, and without relation to the frequency of the carrier wave initially.

In certain situations, as in a carrier wave relay station, it is desired to convert the frequency of a carrier wave to a vdifferent frequency and to control the frequency to which the carrier wave is converted independently of the initial frequency. Where the carrier Wave is modulated as with a television signal, it is cumbersome and -cliicult to reproduce the signal by demodulation of the initial carrier wave, and 'by subsequent modulation of another carrier wave of the desired frequency.

It is relatively simpler to convert the initial frequency of the carrier wave to the desired frequency by heterodyne action. It has been found that such heterodyne action should be provided in a single step to avoid multiple interaction of harmonics with the carrier Vwave produced when more than vone heterodyne operation is used. It is, accordingly, an object of my invention to provide new and improved apparatus for converting the frequency of a television signal modulated carrier Wave in a single heterodyne operation, and for controlling the converted frequency of the `carrier Wave independently of its initial frequency and of the television signal modulations of the carrier wave.

The features of my invention which I `believe to be novel are set forth with particularly in the appended claims. My invention itself, both as to its organization and manner of operation, together with further objects and advantages thereof may best be understood by reference to the following description taken in connection with the accompanying drawing in which the single figure of the drawing illustrates schematically apparatus embodying my invention.

In the figure I have represented at III an antenna arranged to receive a carrier wave modulated n accordance with a television signal. This carrier wave is amplified in a televsion carrier wave amplifier II and is supplied to a frequency converter discharge device I2, which is also supplied with a Vsecond carrier wave generated in an Yoscillating electron discharge `device I3. The carrier Wave generated by the device I3 is multiplied in frequency by the frequency multipliers I 4 to a frequency at which suitable heterodyne operation in the device I2 may be obtained by the waves from the antenna I0 and the waves from the frequency multipliers I4,

The carrier wave resulting from heterodyne operation in the frequency converter device I2 is amplified through a power amplifier device I5 and radiated from an antenna I6.

The frequency of the carrier wave impressed on the antenna Iii is compared in a second frequency converter device I1 with a carrier wave of standard frequency from a crystal oscillator I8. The output of the frequency converter device Il is of a low frequency, which varies similarly to frequency variations of the carrier Wave on the antenna I6, such frequency variations being detected in a rectifying discharge device 35 to control a discharge device I9 arranged to simulate a reactance and s o connected as to control the frequent7 Of Operation of the oscillating device I3.

Upon .any variation in frequency .of the `car rier wave at the antenna I6, the output of the converter .device II varies in frequency in such direction that the detecting `device ,35 by means of the reactance device I9 varies the operating frequency of the oscillating device I3 in such sense as to return the frequency of the carrier Wave at the antenna I6 to a desired value.

The frequency converter device I2 may, as illust-rated, conveniently include a push-pull ra.- clio ,frequency power amplifier having tWo cathodes ,250 connected together and to ground, and two .control .electrodes `2| and 22 connected to opposite terminals of a broadly tuned circuit in cluding an inductance 23, a condenser 24, and a resistance 25. A center tap .of the inductance 23 is connected through an inductance 4I to a suitable negative potential tap of the source 2] to .supply negative bias potential to the control electrodes 2| and 22, .the negative tap being connected to ground for high frequency current through a suitable condenser 28. The screen electrodes 29 of the twin electron discharge device I2 vare connected together, through .a con.- denser `30 to ground for high frequency currents, and to a positive potential tap of the lsource 21, of which a-n intermediate tap is grounded. The two anodes 3| and 32 `of the device I2 are connected `to opposite terminals of a tuned transmission li-ne 33 arranged in balance, .or pushpull relation, and coupled to a tuned transmis,-

Y acts as a balanced modulator, the output of the television carrier amplifier II being impressed across the tuned circuit 23, 24, 25 through a concentric transmission lineV 36 which terminates near the inductance 23 in a series tuned circuit 25, resonant at the frequency of the output of the amplier II, the inductance of the tuned circuit being coupled with the inductance 23. Since the control electrodes 2l and 22 of the device I2 are driven in parallel from the tuned circuit 4I, 42, and the anodes 3l and 32 are connected with the balanced output circuit 33, substantiallyY no energy from multipliers I4 appears in the output circuit 33, so long as there is no output from the amplifier I I.

In the presence of a carrier Wave from the amplier II to be converted in frequency and a wave from the multipliers I4, heterodyne action Y occurs in the frequency converter device I2, and

a wave of heterodyne beat frequency appears in the output tuned circuit 33. The tuned circuit 33 may be tuned either to a frequency which is the sum of the frequencies from the antenna I and from the frequency multipliers I4, or to the frequency which is the difference thereof. It is preferred that the frequency to which the outputl circuit 33 is tuned be substantially different from the frequency of either one of the carrier Waves impressed on the control electrodes 2I and 22, and from harmonics thereof. That carrier wave which is impressed on the control electrodes 2I, 22 and which is nearer in frequency to the resonant frequency of the output circuit 33 should be impressed on the control electrodes in parallel. That is, if the carrier Wave received by the 'antenna IU is nearer in frequency to the output radiated from the antenna I6 than is the carrier wave from the multipliers I4, it is preferred v that the carrier wave from the antenna III be impressed on the control electrodes 2I and 22 in parallel, and the output of the multipliers I4 on both control electrodes in push-pull, or bals resonant at the frequency of the carrier wave on Ythe antenna I6, to ground. This tuned circuit 45 is coupled with a series tuned circuit 46 connected between the terminals of the concentric conductor 43. The cathode 41 of the frequency converter device I1 is connected through a bias;

, ing resistance 48 in shunt with a suitable bypassing condenser 49 to ground, and the control electrode 50 of the device I1 is connected to ground through a tuned circuit I. VThe tuned circuit 5I is resonant at the frequency of the output of an electron discharge amplifier device 52, energized from the crystal oscillator I 8.

The carrier Wave from the power amplifier I5 may be impressed on the second, or screen, electrode 3170i the device I1, instead of on the supi' pressor electrode 44. In such case,'the resonant circuit 45 may be connected between the screen electrode 31 and a suitable positive potential tap on the source 21, in place of the resistanceV 38. In that case, the bypassing condenser 39 connected between the screen electrode 31 and the cathode 41 should be omitted, and the suppressor electrode 44 connected directly to the cathode 41. It is preferred in the present case to impress the carrier Wave from the power amplifier I5 on the suppressor electrode 44, so that the screen electrode 31 acts as an electrostatic shield between the suppressor electrode 44 and the'control electrode 50, so as to reduce interaction between the waves from the power amplier I5 and from the crystal oscillator I8.

The crystal oscillator I8 includes a suitable frequency determining element, such as a quartz crystal vibrator 53 suitably connected in circuit with a discharge device 54 to maintain oscillation of a predetermined highly stable frequency. The crystal oscillator I8 may also include suitable frequency multipliers to provide that the output frequency may be higher than the operating frequency of the vibrator 53, the device 52 being also arranged as a multiplier if desired. The anode 60 of the device I1 is connected through a tuned circuit 6I to a suitable positive potential tap of source 21, and is resonant at a frequency which is the sum or difference of the frequencies of waves from the power amplifier I5 and the crystal oscillator I8. It is preferred that the frequency at which the circuit 6I is resonant be the difference frequency, in order that a relatively low frequency may be utilized for the rectifying device 35, and in order that the changes of frequency of the waves from the power amplifier I5 may appear as equall changes of frequency of a lower frequency wave, thereby being frequency changes of such lower frequency wave of a large percentage of its lower frequency.

The heterodyne output of the frequency converter device I1 which appears inthe tuned circuit 6I is amplified through a suitable amplifier 62 and appears in a tuned circuit 63.

The device 35 may conveniently comprise a pair of rectifying discharge paths respectively having anodes 10 and 1I and catliodes 12 and 13.

A tuned circuit 14, coupled to the tuned circuit 63, is connected between the anodes 10 and 1I, and a center tap of the tuned circuit 14 is electrostatically coupled through a suitable condenFr ser 15 to one terminal of the tuned circuit 63, the other terminal being grounded. A pair of resistances 16 and 11 are connected in series between the cathodes 12 and 13 of the device 3-5, these resistances being shunted by suitable condensers 18 and 19 having low reactance at the Vfrequency of the output of amplifier 62. The center tap of the tuned circuit 14 is conductively connected through an inductance with a point between the resistances 16 and 11 and thereby quency increases, and conversely when the frequency decreases. Y

Thus, if the frequencyof the output of amplifier 62 increases above or decreases below the frequency to'which the tuned circuits 63.and 14 are resonant, the unidirectional voltages across the two resistances 16 and 11 become accordingly positive or negative in potential. So long as the output of the amplifier 62 is of the frequency to the anode III) `and the cathode III. Such volt,- age on the control electrode 92 resultsin leading current flowing between the anode III'I and the cathode III, with the result that the discharge path of the device I9 appears capacitive. The magnitude of this capacitive effect is controlled by the average bias potential of the con,- trol electrode 92, which is adjusted in accord.,- ance with the average potential across the resistances 'I6 and .'I'I as explained heretofore.

oscillations maintained in the tuned circuit |06 by the discharge device I3 are coupled through a suitable condenserv I2U,to the input of the frequency multipliers I4, where the frequency Yof such oscillations is multiplied any desired amount, to be transmitted through the concentric transmission line 40 as explained previously. Since the capacitive efectof the discharge path of the device I9 is adjusted in accordance with the average potential across the resistances 'I6 and TI, the frequency of the oscillations from the frequency multipliers I4 is varied through the agency of the discharge device I9 operating with the tuned circuit |06 in accordance with changes in frequency of the output of power amplifier I5. The polarity of the voltage across the resistances 16 and 'II is such that a change in frequency of the output of the frequency multipliers I4 is in a direction to maintain the output of the power amplifiers I5 at constant frequency.

By the use of the frequency multipliers I4, the frequency change in the Wave transmitted through the concentric transmission line 40 in response to an average potential across the resstances 'I6 and 'I'I is made large. The frequency discriminator device 35 may be so arrange-d as to produce a voltage across the resistances I6 and I'I suflicient to change the simulated reactance of the device I9 by a large amount, since the device I9 need respond to nov voltage except that produced by the discriminator device 35. In consequence of these two effects, a small change ,in frequency of the output of the amplifier I5 tends to produce a very large complementary frequency change in the output of the frequency multipliers I4, so that the stabilizing effect of the arrangement is very large. It has been found, within the range of operation of the discriminator device 35, that the output of the power amplii-lers I5 is to a high degree independent of the frequency of the carrier wave received on the antenna IIJ. In fact, it has been found thata control ratio of 100 can be attained. That is, the output of amplifier I5 would change 1000 cycles without the control arrangement, it changes only 10 cycles with the control system operating.

In a particular case, the frequency of the carrier wave received by the antenna I0 was 163.25 megacycles, the carrier wave being modulated by a standard television signal, and the frequency of the carrier wave radiated by the antenna I6 was 67.25 megacycles. The discharge device I2 was a type 832. push-pull radio frequency beam power amplifier. The average frequency of operation of the oscillating device I3 and tuned circuit |06 was 6 megacycles, andl the frequency of the output of the frequency multipliers I4 was 96 megacycles, the frequency being multiplied sixteen times in the frequency multipliers I4. The output frequency of the crystal oscillator I8 and device 52 was 60.8 megacycles, so that the output frequency of the converter device I'I was 6.45 meacycles. y

In that system, al change in frequency of jthe output of the power amplifier I,5V of 0.01 percent ,produces a change in frequency `of the wave applied to the discriminator device of more than 0.1 per cent, and the discriminator device 35 was arranged to respond to that change in frequency vand control the reactance device I9 so as to produce 4several per cent change in frequency of the operating device I3 and tuned circuit |06. This change in frequency was amplied sixteen times to the frequency multipliers I4, so that a oscillator I8 and device 52 should be such that vthe harmonics thereof differ substantially not only from the frequency of the carrier Wave ref ceived by antenna I0, but also from the frequency of the carrier wave radiated by antenna I6. Similarly, the frequency of the output of converter devices II and I3 should not have harmonics near the carrier wave frequencies on antennas I 0 and I6.

While I have shown and described a particular embodiment of my invention, it will be obvious to those skilled in the art that changes and modications may be made without departing from my invention in its broader aspects, and I, therefore, aim in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In a'high 4frequency carrier relay system, a receiver for a high frequency carrier wave subject to frequency variations, a carrier Wave transmitter, and a frequency converter connected to 'convert the high frequency carrier wave received in said receiver to a desired frequency and to supply oscillations of said desired frequency to said transmitter to control the frequency of the carrier wave transmitted thereby, and means to regulate the frequency of said carrier wave transmitted by said transmitter, said means comprising a second frequency converter constructed and arranged to produce oscillations having a frequency dependent on the frequencyof said transmitted carrier but low relative -thereto, a low frequency oscillator, means to control the fre'- quency of said low frequency oscillator in response to variations in frequency of oscillations produced by said converter, and a frequency multiplier connected between said low frequency oscillator and said first converter to supply a harmonic of said low frequency oscillator -tosaid converter to beat with the received carrier to produce said oscillations transmitted by said transmitter.

2. In a carrier relay system, the combination of a receiver for carrier waves of frequency subject to variation, a carrier wave transmitter, and frequency conversion means constructed and arranged to combine said received carrier wave with locally produced oscillations to produce oscillations to be transmitted' andto supply said oscillations to said transmitter'to control the frequencies of oscillations transmitted thereby, said receiver, transmitter and conversion means 'all operating .at short wave lengths, and means to maintain constant the frequency of said transwhich the circuits 63 and 14 are resonant, there is no net voltage across the resistances 16 and 11. Consequently, whenever the output of the power amplifier I varies from a frequency equal to 'the sum (or the difference as Vthe case may be) of the frequency to which theV circuits 63 and 14 are resonant and the frequency of the output' of crystal oscillator I8 and device 52, a voltage appears across the resistances 16 and 11 whose polarity is in accordance with the directio-n in which the frequency of the output of the amplier I5 differs from its desired frequency This voltage across the resistances 16 and 11 is utilized to causey the frequency of the output ofthe amplifier I5 to return to its assigned frequency.

The cathode 13 is connected to ground, and the cathode 12 is connected through two serially connected resistances 90 and 9| to the first, or

low pass filter circuit with the resistance 90 to prevent rapid variations of potential on the control electrode 92 in response to rapid variations in potential across the resistances 16 and 11.

Since the carrier wave received by the antenna I0 is modulated, and such modulations are retained on the carrier wave from the power amplier I5, these modulations are applied through the frequency converter device I1 and amplifier 62 to the frequency discriminator device 35. Acccrdingly, any frequency change in the carrier wave applied to the frequency discriminator device 35, being either a fortuitous or intentional change of carrier frequency, produces a change of potential across the resistances 16 and 11. The televisionV signal with which the carrier wave is modulated may include synchronizing pulses whichshift or modulate the carrier frequency rather than modulating carrier amplitude above the black level, so that the resulting voltage pulses across the resistances 16 and 11 may occur at the rate of the synchronizing pulses in the television signal.

Furthermore, modulation of a carrier waver in accordance with a television signal is usually accomplished in suchV a fashion that only vestigial side bands are transmitted on one side of the carrier frequency. If the carrier wave be'modulated in amplitude in accordance with the television signal, the greater energy in one side band may appear to the frequency discriminator device as a shift in carrier frequency.

If the carrier wave be modulated in frequency in accordance with the video portion of the television signal, the major portion of the energy lies in a frequency band centered around the carrier frequency, but where vestigial side band transmission is used in such a system, the remaining energy is predominately of a frequency different fromcarrier frequency, and may fortuitously appear to the frequency discriminator device 35 as a`shift in carrier frequency. In order to avoid the possible effect of all these modulations of the carrier frequency, as by synchronizing pulsesorV video signals, on the fre-l tively near its assigned frequency, and do` notY transmit it to any substantial extent when the frequency of the carrier Wave is shifted, as in accordance with the synchronizing signal.

The vertical pulse's'of the synchronizing signal may have a low repetition rate, such that the carrier Wave is interrupted in its transmission to the resistances 16 and 11 at the rate of 30 times per second. It is not desired that such modulation of the Voltage across resistances 16 and 11 influence the vaverage carrier frequency, ,and accordingly means is provided whereby the bias potential on the control electrode 92 of, the reactance device I9 is prevented from changing in response to such voltage changes across the resistances 16 and 11.

The means for preventing rapid voltage changes across the resistances 16 and 11, such as may be caused by interruption of the carrier wave impressed on discriminator device 35,' is the low pass filter including resistance .90 and .condenser 93. The time constant of this resistance and condenser 93 should be suii'iciently large that a rapid change of voltage on resistances 16 and 11 does not appreciably affect the potential of .the control electrode 92. In the case described where the frequency of the carrier wave is modulated,for example, thirty times per second by vertical synchronizing pulses, the time constant of the resistance 90 and condenser 93 may be made of the order of l/ao of a second or more. That is, the resistance 90 may, for example, be about 200,000 ohmsvand the condenser 93 be about 0.2 microfarad. n

The cathode |00 of the discharge device I3 is connected to ground, and the control electrode IUI is connected through a suitable grid bias resistance |01 to ground. The anode |02 of the device I3 is connected through an inductance |03 to a suitable positive potential tap of the source 21 of potential, which tap is connected yto ground through a suitable bypassing condenser |04. The control electrode |0| of the device I3 is connected through a coupling condenser |05 to one terminal of a tuned circuit |06, of which the other terminal is connected to the tap of the source 21 which is grounded through the condenser |04. The inductance |03 and the tuned circuit |06 are electromagnetically coupled, so that the device |3 maintains oscillations in the tuned circuit |06 at its resonant frequency.

The discharge path of the reactance device I9 is connected for high frequency currents in shunt to the tuned circuit |06, so that leading or lagging currents passing through the discharge path of the device I9 change the resonant frequency of the tuned circuit |06. The anode IIII of the device I9 is connected to a point between the coupling condenser |05 and tuned circuit |06, and the cathode III of the device I9 is ccnnected through a suitable biasing resistance I I2 in shunt to a bypassing condenser -I I3 to ground. A condenser ||4 is connected between the anode I|0 and a control electrode 92 of the device I9, the reactance of the condenser I I4 being high at the frequency of oscillation of the tuned circuit |06. The second, or screen, electrode II5 of the device I9 is connected through a suitable condenser II6 to the cathode III, and through a resistance I I1 toa suitable positive potential tap of the source 21 of potential.

The condenser '|I4 and the resistance 9| act as a phase shifting network connected for highY the resistance 9| is nearly a quarter wave ad- Y vanced in phase with respect to voltage between mitted carrier wave notwithstanding variations in frequency of said received carrier Wave, said means comprising a local oscillator of xed frequency differing by a low frequency from that of the transmitted carrier wave, means to combine oscillations having the frequency of said transmitted carrier wave with oscillations produced by said fixed frequency oscillator to produce oscillations Varying in frequency in accord the percentage variation in frequency of said transmitted carrier wave, a local oscillator operating at 10W frequency, means to regulate the frequency of said low frequency local oscillator in accord With variations in frequency of oscillations produced by said combining means, and a frequency multiplier connected between said low frequency oscillator and said frequency conversion means to supply to said conversion means with Variations in the transmitted carrier wave 10 said locally produced oscillations.

but by a percentage Variation far greater than HENRY B. FANCHER.

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