Contains reports on four research projects.National Aeronautics and Space Administration (Contract NASw-33)Lincoln Laboratory (Purchase Order DDL B-00283)United States ArmyUnited States NavyUnited States Air Force (Contract AF19(604)-5200

Badessa, R. S.

Bates, V. J.

Buhl, D.

Cogdell, J. R.

Kent, R. L.

Rennick, R. C.

Searle, Campbell L.

Contains reports on two research projects.National Aeronautics and Space Administration under Contract NASw-143Lincoln Laboratory, Purchase Order DDL B-00283U. S. ArmyU. S. NavyU. S. Air Force under Air Force Contract AF 19(604)-520

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X. SATELLITE TIME-DILATION MEASUREMENTProf. J. R. Zacharias V. J. Bates B. L. DiamondProf. C. L. Searle D. Buhl R. HuibonhoaProf. J. W. Graham J. R. Cogdell R. L. KentR. S. Badessa R. C. RennickInvestigations are being carried out in preparation for a short-term measurement ofgravitational red shift in an earth satellite. System design studies and preliminarycircuit construction and testing are continuing. Also, short-term stability measure-ments on highly stable quartz crystal oscillators are being performed.A. Gravitational Red Shift Investigation1. Measurement systema. System stability. The advantages of a cw system as compared with a pulse sys-tem for the communication link with the satellite were presented in Quarterly ProgressReport No. 57 (page 179). A serious problem with the cw system is the possibility of450 MC+908 15MC+3811.25MC d+908 26.25MC-d + 938 426.25MC -d+17381-F AMPLIFIER I-F AMPLIFIER POWER AMPLIFIER438.75MC+d 400 MC + 8082875MC -d+93.58 428.75MC - d+1735I-F AMPLIFIER POWER AMPLIFIERRECEIVING TRANSMITTINGANTENNA ANTENNA17.5 MC+ 3.58Fig. X-1. Proposed satellite equipment for cw operation. (Ground-transmitter frequency, 438. 75 mc; 8 is gravitational redshift of 5-me oscillator; d is first-order Doppler shift.)self-oscillation in the satellite as a result of spurious generation of the received signalin the mixers and harmonic generators. To determine whether or not the satellite systemthat is now under consideration (Fig. X-l) would present this difficulty, a portion of thesatellite receiver was constructed and tested. There are four rf signal frequencies thatwould be present, together with the desired signal from the ground transmitter. Thesesignals were applied to the satellite receiver input (Fig. X-2). The ground-transmitter* This work was supported in part by National Aeronautics and Space Administrationunder Contract NASw-143; and in part by Purchase Order DDL B-00283 with LincolnLaboratory, a center for research operated by Massachusetts Institute of Technologywith the joint support of the U.S. Army, Navy, and Air Force under Air ForceContract AF 19(604)-5200.127(X. SATELLITE TIME-DILATION MEASUREMENT)LOCALOSCILLATOR450 MC (5mw)I-F AMPLIFIER TO HIGH-FREQUENCYMIXER11. 25MC OSCILLOSCOPE4538.75-MC X / 4SIGNAL400MC SPURIOUS(O.Imw) SIGNALS428.75 MC(O.Imw)426.25 MC(0.1mw)Fig. X-2. Arrangement for investigation of stabilitywith spurious signals.signal was included in order to check the receiver performance. When this signal wasremoved, the output of the i-f amplifier was reduced to noise, which indicated satis-factory performance in the presence of spurious signals.In conjunction with the proposed satellite experiment, a frequency synthesizer wasconstructed to furnish all of the pertinent signals from a 5-me frequency standard.b. Transistor UHF power amplifier. Two power amplifiers at a frequency of425 mc are required to provide suitable satellite transmitter signal levels for the pro-posed experiment. To investigate the capabilities of transistor amplifiers in this appli-cation, a two-stage amplifier was designed and constructed. A Western Electric 2N1195transistor (225-mw power dissipation, 750-me alpha cutoff frequency) was used as thedriver, and a Texas Instrument 2N1142 transistor (750 mw, 600 mc) as the output.Design specifications called for a 20-db power gain with a 0. 5-mw drive level. Theactual output power level of 20 mw represented a power gain of 16 db. Further investi-gation of transistor amplifiers will be postponed until the oscillator stability require-ments are achieved.c. Low-frequency reference-signal generation. A system has been constructed toprovide selected low-frequency reference signals for determination of the relativisticfrequency deviation of the received signal at the ground station. A series of discretefrequencies in 2-cps steps from 490 cps to 510 cps is generated as shown in Fig. X-3.The 10-kc output from an HP 100D secondary frequency standard is divided down to2. 5 kc and modulated with narrow pulses at a rate of 10 cps to provide a "comb" spec-trum centered at 2. 5 kc. The spectrum is transferred to 100 kc by mixing with a102. 5-kc signal obtained from a voltage-tunable oscillator. The 100-kc comb spectrumis then applied to a crystal filter with sufficient selectivity to pass only one component128FREQUENCYSELECTORINPUT2.5KC+IOn CPS)ER500 + 2n CPSFig. X-3. Low-frequency reference generator.BALANCEDMIXERFig. X-4. Oscillator stability-measurement system.12910 KC(FROMHP IOOD)IOCPS(FROMHP IOOD)(X. SATELLITE TIME-DILATION MEASUREMENT)of the spectrum. The tunable oscillator is phase-locked to a selected component bymeans of a 100-kc phase detector that compares the crystal-filter output with a 100-kcreference signal from the frequency standard. The final output at 490-510 cps is obtainedby mixing and frequency division from the phase-locked oscillator.The measured stability of the output was found to be ±2 X 10 - 4 for a measurementinterval of 0. 02 sec (10 cycles at 500 cps), as a result of residual 10-cps modulationof the signal. For measurement intervals of 1 minute or longer, however, the stabilityis essentially that of the secondary standard, which is stated to be ±1 X 10 - 6 . For agravitational red shift measurement at 500 mc, the low-frequency reference stability issufficient to permit a measurement accuracy of 1 per cent.B. Oscillator Stability StudiesIn order to permit short-term frequency comparison of two highly stable quartzoscillators, a system of frequency multipliers and mixers, shown in Fig. X-4, is beingassembled. An effective multiplication of frequency difference by approximately 10, 000is provided. The output phase difference is displayed unambiguously on an oscilloscopeand can easily be determined with an accuracy of 150 at any instant. Thus, a frequencydifference between oscillators, averaged over a 100-sec interval, can be measured withan accuracy ofAf = 15 4 10-14- -4X10f Tf N 6 4o 3600 X 100 X 10 X 10The measurement accuracy is approximately two orders of magnitude greater thanthe desired oscillator stability.C. L. Searle, R. S. Badessa, V. J. Bates, D. Buhl,J. R. Cogdell, R. L. Kent, R. C. Rennick130

Satellite Time-Dilation Measurement

XIX. SATELLITE TIME-DILATION MEASUREMENTProf. J. R. Zacharias V. J. Bates B. L. DiamondProf. C. L. Searle D. Buhl R. HuibonhoaProf. J. W. Graham J. R. Cogdell R. L. KentR. S. Badessa R. C. RennickA. GRAVITATIONAL RED SHIFT INVESTIGATION1. IntroductionSeveral possible communication systems for frequency comparison in the proposedsatellite gravitational red shift experiment have been considered. Preliminary findingsindicate that a cw system utilizing a frequency offset is the most suitable. The advan-tages of the cw system can be summarized as follows:(a) Since the satellite transmitter will employ transistor output stages that areessentially peak-power-limited, highest average power will be received at the groundstation if a cw system is employed.(b) There is no need for high-speed, signal-controlled switching in the satellite, aswould be required in a pulsed system to avoid oscillation caused by spillover; instead,the frequency offset between ground and satellite transmitters guards against instability.(c) The satellite equipment is considerably less complex than that which would berequired for a pulsed system.The disadvantages of the cw frequency-offset technique are:(a) There is a possibility of self-oscillation in the satellite as a result of spuriousgeneration of the signal frequency in mixers and harmonic generators.(b) The complexity of the Doppler-cancellation operations required in the groundinstallation may tend to obscure the basic simplicity of the method.Several precise frequencies in the 1 mc-500 mc range are employed in the cw sys-tem (for example, of local oscillators, transmitters, etc.), and a frequency synthesizeris being constructed to obtain all such frequencies from a single 5-mc crystal-controlledoscillator. Signals obtained from this unit will be mixed, amplified, and so on, toinvestigate the generation of undesired signals that might cause measurement errorsor instability.Transistor i-f amplifiers and i-f and uhf power amplifiers are under development.Effort is also being devoted to the possible use of tunnel diodes in the satellitereceiver and to the problem of reference-signal generation for frequency comparisonat the ground station.This work was supported in part by National Aeronautics and Space Administrationunder Contract NASw-33; and in part by Purchase Order DDL B-00283 with LincolnLaboratory, a center for research operated by Massachusetts Institute of Technologywith the joint support of the U.S. Army, Navy, and Air Force under Air ForceContract AF 19(604)-5200.179(XIX. SATELLITE TIME-DILATION MEASUREMENT)2. Transistor UHF Power AmplifierIn conjunction with the satellite gravitational red shift investigation, a 425-me tran-sistor transmitter is being designed. As a preliminary step, measurements are beingmade of input impedance, output admittance, and power gain of several transistors atthis frequency. The measurement has been completed for a silicon mesa transistor(Motorola type 2N700) in the common base configuration. For a conjugate-matchedstage at 425 mc, the results are:power gain : 10 dbinput impedance : 50 + j300 ohmsoutput admittance : 0. 0015 + j0. 012 mhoAfter measurement of these parameters and the common-base h-parameters of severaltransistors, a two-stage transistor power amplifier to yield 50-100 mw at 425 mc willbe designed and constructed.3. Low-Frequency Reference-Signal GenerationThe data-analysis equipment for the proposed experiment requires a highly stableand tunable low-frequency reference signal. The signal received at the ground stationfrom the satellite will be mixed to a frequency of approximately 500 cps. The frequencydeviation to be measured represents approximately one part in 104 of this receiveroutput frequency. A comparison will be made with a reference signal of nearly thesame frequency, in order to determine the relativistic frequency shift.In order not to degrade the experimental accuracy, the low-frequency referencesignal should be accurate within a few parts in 10 6. In order to compensate for long-term drifts between the oscillators that are being compared, the low-frequency referencesignal will be tunable over a range of ±40 cps in 2-cps steps. Effort is being devotedto the design and construction of a simple but accurate source for these reference sig-nals.C. L. Searle, R. S. Badessa, V. J. Bates, D. Buhl,J. R. Cogdell, R. L. Kent, R. C. Rennick180

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Satellite Time-Dilation Measurement

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