I ntroduction

Planetary RadioAstronomy Receiver

GENE J. LANG, Member, IEEEMartin Marietta Corporation

ROBERT G. PELTZER, Member, IEEEUniversity of Colorado

Abstract

Voyager (Mariner Jupiter/Saturn 1977) spacecraft will carry the

first experiment specifically designed to measure low-frequency

nonthermal planetary radio emissions. The technical aspects of the

planetary radio astronomy instrument are described here. Signals

from 10-m orthogonal monopoles are processed to measure polariza-

tion and for either maximum sensitivity or observation of rapid

temporal variations. The 0.3-,uV/v/iäiH (i.e., -117 dBm/kHz with a

50-12 source> sensitivity and the 140-dB dynamic range achieved

allow signals to be observed from near earth through planetary en-

counter. Stepped- or fixed-frequency operation is commandable

over a range of 1.2 kHz to 40.5 MHz with internal calibration for

absolute amplitude measurement.

Manuscript received January 12, 1977; revised May 2, 1977. Copy-right © 19 7 7 by The Institute of Electrical and Electronics Engineers.Inc.

The Martin Marietta Corporation is the contractor for the planetaryradio astronomy receiver under Contract P.O. 48319 administeredby the University of Colorado. The overall experiment responsibil-ity and science team direction are performed by the University ofColorado under Contract 953592 to the Jet Propulsion Laboratory.

Authors' addresses: G.J. Lang, Martin Marietta Corp., P.O. Box 179,Denver, CO 80201; R. G. Peltzer, University of Colorado, Boulder,CO 80309.

For over 20 years ground-based radio astronomers have ob-served nonthermal radio emission from Jupiter at frequen-cies above those where the terrestrial ionosphere is opaque.Ground-based systems have been developed to discriminatethese strongly circularly polarized signals from the linear orrandomly polarized cosmic, terrestrial magnetospheric,solar, and man-made emissions. Experiment capability hassubstantially increased since the first satellite measurementof cosmic background below the ionospheric cutoff in1959 [1]. The most advanced space-qualified radio astron-omy instruments flown to date are the Radio AstronomyExplorer-2 and the Helios spacecraft instruments. Datafrom these and previous instruments have contributedsignificantly to the science of radio astronomy even thoughthey are less complex than the instrument described here[2], [3]. The scientific objectives of this experiment willbe presented pending review, in a forthcoming issue ofSpace Science Review [4].

The planetary radio astronomy (PRA) experiment hasbeen optimized for planetary observations from theVoyager spacecraft. This instrument will measure theamplitude, spectrum, time variations, and polarization ofradio emissions over a frequency range of 1.2 kHz to 40.5MHz using the PRA receiver (PRAR) and two 10-m orthog-onal monopoles. Sensitivity and dynamic range will allowobservation of a wide range of Jovian emissions from nearearth to encounter 12 years later. Jovian measurementswill continue in transit to Saturn but will be phased out infavor of Saturn emission measurements by encounter withSaturn 4 years after launch. If the Uranus mission optionis exercised by Voyager, Uranus emissions will be searchedfor 9 years after launch.

The opportunity to make both long-term observationsduring cruise and close-in measurements during encounterof the planets will provide data to support the followingobjectives:

1) locate the source and explain the mechanism ofJupiter's radio emissions;

2) detect magnetic fields of the outer planets;3) measure planetary radio emissions and their relation-

ships with the planets' satellites;4) measure plasma resonances in the magnetospheres of

Jupiter and Saturn;5) determine whether lightning occurs on the giant

planets;6) compare planetary and solar radio bursts in space

with those seen on earth and observe solar radiobursts from the far side of the sun.

System Design

PRAR design represents a large increase in capabilitywhen compared with previous satellite-borne receivers. Thisreceiver can discriminate polarization, has a significantlyincreased frequency range and resolution, and has a highdegree of operational flexibility. This flexibility will allow

IEEE TRANSACTIONS ON AEROSPACE AND ELECTRONIC SYSTEMS VOL. AES-13, NO. 5 SEPTEMBER 1977466

response to a wide range of excitations and useful operationwith certain elements inoperative. The instrument has beendesigned to "fail soft." For example, a failure of one of theintermediate frequency (IF) channels or in the frequencysynthesizer loop will not significantly degrade the scientificmeasurements since the two IF channels are almost fune-tionally redundant and the local oscillator (LO) can beswitched to a calibrated open-loop mode. The instrumentdesign makes full use of the flexibility obtainable from thespacecraft flight data subsystem (FDS). The FDS softwarecan be programmed from the ground to rearrange thesequencing of the operating modes and to select the fixedoperating frequencies of the PRAR.

The PRAR design was strongly influenced by the usualspacecraft restrictions on weight and power as well as bythe additional unique restrictions of radiation tolerance, a4-year operating life after launch, and intense electromag-netic (EM) fields at Jupiter. Physical and performanceparameters are summarized in Table 1. Flexibility is exer-cised through ground command of the functions shown inTable II.

The operating modes are combinations of the followingfour variables:

1) fixed- or step-scanned frequency;2) low-frequency IF set to measure on or between space-

craft power inverter harmonics;3) 25-ms detection time constant with 30 ms/step or

0.1-ms time constant with 0.14 ms/2 steps;4) polarization switch which reverses each step or is fixed.

Fig. 1 shows the PRAR functional elements with associatedoperating frequencies. The preamplifiers provide the im-pedance transformation from high-impedance orthogonalantennas to 50 2, overload protective circuitry, and com-mandable attenuators. The outputs are buffered to simul-taneously drive the low-frequency (LF) and high-frequency(HF) bands. Mixers in each band convert signals to fixedIF and circular polarization is discriminated with 90-degreequadrature hybrids.

Harmonics from the 2.4-kHz spacecraft inverter havelarge amplitudes within the 1.2-kHz to 1.3-MHz LF bandrange. Selection of 19.2 kHz (eighth harmonic of 2.4 kHz)as the step frequency with 1.2 kHz as the lowest frequencypermits narrow bandwidth (1 kHz) measurements to bemade midway between power supply hannonics. A fre-quency synthesizer locks the LO to the spacecraft inverterfrequency to center the LF-IF filter passbands between the2.4-kHz inverter harmonics. Above 1.2288 MHz (512thharmonic of 2.4 kHz) a wide bandwidth (200 kHz) is usedwith a 307.2-kHz step.increment. A 6-s scan of the 1.2-kHzto 40.5-MHz range is used.

Dual conversion of HF band signals to the LF band IFamplifier frequency allows common use of a large portionof the amplification and data processing circuitry. A 307.2-kHz offset in the second conversion LO's produces a one-step offset in the frequeneies measured by the two channelsin the HF band. Most of the system gain is in the third andfourth LF-IF's. Log-IF's convert a 50-dB input range to a

TABLE

Physical and Performance ParametersParameter

Frequency RangeFrequency StepsStep Increment

IF Bandwidth

Sensitivity

Polarization DiscriminationFrequency S tabilityComsandable Attenuation

Logarithmic Dynamic RangeInput ImpedancePostdetection Time ConstantData Rate (Average)Frequency Range Scan Time

Calibrator

Operating Modes

Power

Weight (Without Antennas)Size

Radiation Tolerance

Operating Life

Temperature Range

LF Band

1.2kHz to 1.33MHz70

19.2kHz

1kHz0.3mV/ki

HF Band

1.2 MHz to 40.5MHz

128

307. 2kHz200kHz0. 14V/ z

20dB10-5 for 4 years

0-90dB in 15dB stepsDual slope, 50dB

22MQ + 12pF25ms, D.lms in high data rate mode

266bps, 115.2kbps in high data rate mode

6 seconds

3 levels + off (1.2kHz to 40.5MHz)6 primary6.7W (2.4kHz, 50V square wave)9.7 lb (4.4kg)12x10x4 in. (0.3x0.25x0.10 m)5 x 1012 electronslcm2, 3 MeV equiv.4 years in space envirorment

-30 to 850C

TABLE 11Ground Commandable Functions

Function Alternatives

Operating Mode 6 primary (14 useful)Frequency 200

Attenuator Combinations 7

Calibrator On1OffCalibrator Injection Selection Upper Channel/Lower Channel/BothCalibrator Injection Bypass In/OutPolarization Polarity Reversing Each SteplFixedSynthesizer Phase-Locked Loop Open/ClosedChannel to Data Processor Upper/Lower or Alternating

5-V video output range. A dual logarithmic slope is usedfor increased sensitivity at low signal levels. Video data areeither smoothed with a 0.1 -ms filter in the high data ratemode or integrated for 25 ms in the low data rate mode andthen converted to digital format and transmitted to thespacecraft via interface circuits.

Inflight end-to-end calibration of circuit gain is achievedby injecting wideband stable calibrator noise into the pre-amplifier.

Preamp/Attenuator/Calibrator

A functional block diagram for the PRAR preamplifierand calibrator circuitry is shown in Fig. 2.

The low noise input buffer circuitry consists of a2N441 6A junction field effect transistor (J-FET) withcurrent regulation, bootstrap circuit, and buffer amplifiersto obtain high input impedance and the ability to with-stand a direct RF input of greater than 20 V peak-to-peakwithout damage.

Resistor networks with capacitor frequency compensatior

LANG/PELTZER: PLANETARY RADIO ASTRONOMY RECEIVER 467

i1

1.2 kHz to 40.5504 33i

57 ~~1.2 kHz to

r t~~~.326 MHz

1.2 kHz to 40.5504 MHz 45.1584 MHz

Fig. 1. Simplified PRAR block diagram.

Fig. 2. Preamplifier/calibrator block diagram.

are used for the 45-, 30-, and 15-dB attenuators. Since solid-state switches do not provide sufflcient isolation or constantinsertion loss over the wide frequency and impedance rangesof the preamplifier, miniature magnetic latching relays wereselected for the attenuator switches.

The main gain stage and output buffer driver are videofeedback amplifiers. LF band signals are coupled from thecollector and HF band from the emitter of the driver, there-by obtaining a 50-2 source impedance and buffering forboth bands with a single transistor.A Solitron K672 noise diode supplies a low-level noise

input for the calibrator. Ampliflcation is obtained with avoltage-regulated feedback circuit. The voltage to both the

noise diode and amplifier can be turned off with a transistorswitch to reduce power.A 0.25-dB gain and 1.5-degree phase match between

preamplifiers is required for good polarization discrimination.Extensive use of feedback and regulation densensitizes boththe preamplifier and calibrator response to changes in end-of-life component and voltage values. A stable reference istherefore available for determining gain change of subse-quent circuits. With the internal noise source calibrator, thePRAR should remain an accurate radiometer over the 4-yearmission life.

LF Polarization Discriminator

Signals from the preamplifiers are attenuated above 1.4MHz by a low-pass filter to eliminate direct feedthrough atthe LF-IF frequency of 3.09 MHz and images produced byfrequencies above 6.18 MHz. Each channel is then mixedwith the LO signal, and the resulting signals at the LF-IFfrequency are fed to a 90-degree quadrature hybrid to obtainthe right-hand and left-hand polarization components. Adouble-pole double-throw (DPDT) J-FET switch reversesthe polarized signals prior to the upper and lower firstLF-IF inputs.

First and Second LF-IF

Bandwidth limiting in the LF band is determined byselecting one of two crystal bandpass filters. The primarymode of measurement uses 3.09-MHz filters in a 9-crystalladder configuration to achieve a 1-kHz bandwidth withskirts down 90 dB at 1.2-kHz off-center frequency. Thishigh attenuation will eliminate interference from spacecraftinverter harmonics. The 3.084-MHz filters are used for thealternate mode operation. The passband is centered on the

IEEE TRANSACTIONS ON AEROSPACE AND ELECTRONIC SYSTEMS VOL. AES-13, NO. 5 SEPTEMBER 1977

3.090 or 3.084 MHz 3.087 MHz Video Digital

468

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uM 1500

4>a 100c(

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-100. .-5 -4 -3 -2 -1 0 +1 +2 +3 +4 +5

Relative Frequency, kHz

Fig. 3. First and second LF-IF frequency response.OL 1 1 1 1 -

-130 -120 -110 -100 -90 -80 -70 -60

Input Signal Level, dBm/kHz

Fig. 4. PRAR dynamic response.inverter harmonics with a 3-dB bandwidth of 800 Hz. Theseries combination of DG-133 J-FET switches used to selectthe appropriate filter has a large isolation with respect tothe filter stopband response.

Two LF-IF amplifier stages provide buffering and gain tomake up for the additional circuit and narrowband crystalfilter insertion loss in the LF band compared with the HFband. These amplifiers are tuned single-transistor stages.A DG-133 integrated circuit (IC) is used to select eitherLF-band or HF-band signals. After this point, all remainingcircuitry is common to both bands.

Fig. 3 shows the overall bandpass response of the firstand second LF-IF with the 3.09-MHz filters switched in.

HF Polarization Discriminator

Since planetary radio emissions are much weaker at fre-quencies above 40 MHz [5], [6], no low-pass filtering isneeded to reduce possible direct feedthrough at the 45-MHzHF-IF amplifier frequency. Except for this lack of filtering,the HF polarization discriminator is functionally identicalto the LF polarization discriminator up to the polarization-reversing switch output. The HF polarization switch usesthe same design as the LF circuit with the addition of anLC circuit to resonate with the J-FET junction capacitance.A single resonant circuit effectively resonates both of the.off' FET junctions coupled through the "on" FET's.This simple addition produces an order of magnitude in-crease in isolation.

An HF bandpass filter is used to reject spurious interfer-ing signals located at the desired signal frequency minustwice the LF-IF frequency. The HF-IF is a relatively broadtuned single-stage amplifier.

Translation LO

The translation LO boards each comprise a crystal oscil-lator/amplifier/buffer and mixer. Crystal frequencies areoffset one step as previously noted.

Third and Fourth LF-IF

Gain of the third and fourth LF-IF is 55 dB. The thirdLF-IF and output of the fourth LF-IF are tuned 50-nstages. Two higher impedance video feedback stages in thefourth LF-IF produce most of the receiver voltage gain afterthe 210-kHz band-limiting of the LC bandpass filter. ThisLC filter sets the bandwidth of the receiver in high-bandoperation.

Log-1 F and Detector

A 50-dB dual slope logarithmic response is obtained fromfive successively saturating stages with the diode-detectedsignal from each stage summed with an operational amplifier.The dual slope is generated by adjusting the stage gain andthe detected signal contribution to the summer. The input-to-output response of the receiver is shown in Fig. 4.

Frequency Synthesizer

The voltage-controlled oscillator (VCO) portion of thefrequency synthesizer is shown in Fig. 5. This oscillator cir-cuit uses Alpha DKV 651 5A hyperabrupt junction varactorsfor both coarse control and loop feedback control. Althoughthe primary mode of operation is in a closed-loop configura-tion, should the loop fail, open-loop operation can be com-manded. In this case, a linear frequency response versusstep number similar to the closed-loop characteristic is ob-tained by a temperature stable linearization networkdesigned with only four ordinary diodes, four selectableZener diodes, two thermistors, and associated resistors. Anopen-loop response has been obtained within 2 percent ofthe closed-loop line.

Efficient operation of the buffer and output driver tothe HF mixers is obtained using varactor-tuned class-C

LANG/PELTZER: PLANETARY RADIO ASTRONOMY RECEIVER 49

Control

toMEZ

Fig. 5. Frequency synthesizer.

circuits. The tuned amplifier control voltage is the samesignal that controls the VCO. This signal is obtained froma buffered HI-1080 digital-to-analog (D/A) converter drivenby the same command as the programmable divider in thesynthesizer loop.

Schottky-clamped 54S1 13 flip-flops are used in thefixed-ratio loop divider chain. These devices havebeen screened for 125-MHz operation to ensure adequateend-of-life response. The input to the driver for the LFmixers is obtained by dividing the input to the programmabledivider by 2.

The programmable divider output is compared to halfthe 76.8-kHz reference clock from the spacecraft data sys-tem using a phase detector. The filtered output of thephase detector is used to bias varactor diodes in the VCO toprovide fine-control feedback voltage.

There are 5 ms available for the loop to settle to within25 Hz of the commanded frequency measured at the LFdriver. A 2- to 3-ms settling time has been achieved withappropriate selection of loop active filter response andtraps.

Data Processor

Detected video from the log-IF is filtered with a 0.1 -msRC time constant. In the low data rate modes of operation,the signals are integrated with an operational amplifler for25 ms during each 30-ms period. After integration, the sig-nal is held with a sample-and-hold circuit until processedby the analog-to-digital (A/D) converter. One A/D convert-er is shared between channels with selection by an FETswitch.

In the high data rate mode, the operational amplifier isswitched from integrator action to an amplifier. Bothchannels are sampled simultaneously each 0.14 ms and areserially fed to the A/D converter.

An FET multiplexer is used to commutate signals propor-tional to the PRAR input current, internal voltages, andcoarse-control voltage to a spacecraft analog interface line.

The control system decodes the command words, com-mands or clocks all switches to the required configuration,including the commands for VCO frequency control, andsequences receiver operations. In addition to these primaryfunctions, receiver switch status is generated for transmissionto the flight data system, and all circuits are reset to knownconditions when power is applied.

Power Supply

The 2.4-kHz square-wave power input allows the use ofa relatively simple transformer/rectifier/filter-type powersupply.

Antennas

The 10-m orthogonal monopole antennas are motordeployed interlocked bistem booms. This torsionally rigidinterlocked design provides the mechanical stability neces-sary to limit spacecraft torqueing disturbances to an accept-able value.

The receiver functions as a high impedance voltmeterbecause the source impedance is much less than the pre-amplifier input impedance. Antenna open circuit voltage ishalved by capacitive loading from its support structure andinterconnecting wiring.

Packaging

To obtain a substantial overload capability, most of thesignal amplification is accomplished after IF filtering. Asa result, much of the circuitry operates at low signal levels.This places stringent requirements on controlling self-interference. Thirteen shielded compartments are used withall intercavity power lines filtered and control cables shielded.All RF boards have ground planes that wrap around theboard edges and contact the case around the cavity periphery.The magnesium case is made in two pieces with boards oneach side of each half. A shield is inserted between thehalves when bolted together. Fig. 6 shows the receiver anderectible interlocked bistem antennas.

Performance

Performance parameters and functions summarizedearlier in Tables 1 and II have been achieved. Sensitivity ofthe receiver to 0.3-,iV/VkiHz polarized input signalis compared with the background noise in the lowertwo curves of Fig. 7. This signal level is well above thenoise for all frequencies above 97.2 kHz. Note steps 1) and2) are not observed by the flight data system since statuswords are monitored at this time in the sequence. Theupper curve shows the receiver response to a 30-,uV/Vk}iHflat noise source. The statistical variations produced withthe narrowband filtering of noise can be seen in the LFband data. Polarization discrimination of sinusoidal signals

IEEE TRANSACTIONS ON AEROSPACE AND ELECTRONIC SYSTEMS VOL. AES-13, NO. 5 SEPTEMBER 1977470

Upper Channel.reqreFCy, F31z

0 -4 `n -4

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-30

3

-40

01 r50=~~~~~~~~~~~~~~~~~0 020 40 60 80 100 120 140 160

Step Nu.ber

Fig. 6. PRAR and antennas. Fig. 7. PRAR frequency response and sensitivity.

is above 25 dB for most of the frequency range, falling to20 dB at some points.

References

[1] J.P.I. Tyas, C.A. Franklin, and A.R. Malozzi, "Measurementof cosmic noise at low frequencies above the ionosphere,"Nature, vol. 184, pp. 785-786, Sept. 12, 1959.

[2] J.K. Alexander et al., 'Scientific instrumentation on RadioAstronomy Explorer-2 Satellite," Astron. Astrophys., vol. 40,pp. 365-371, 1975.

[31 R.R. Weber, "The radio astronomy experiment on Helios Aand B," Raumfahrtforschung, vol. 19, pp. 250-252, 1975.

[41 J.W. Warwick, J.B. Pearce, R.G. Peltzer, and A.C. Riddle,"Planetary radio astronomy experiment for Voyagermissions," Space Sci. Rev., accepted for publication.

[51 J.W. Warwick, Radio emission from Jupiter," Annu. Rev.Astron. Astrophys., vol. 2, 1964.

[61 J.W. Warwick, G.A. Dulk, and A.C. Riddle, "Jupiter radioemission, January 1960-March 1975," Univ. ColoradoRadio Astronomy Observatory publication, PRA No. 3,May 1975.

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Gene J. Lang (M'63) was born in Ashville, N.C., in 1935. He received the B.S.E.E. degree in1957, the M.S. degree in 1959, and the Ph.D. degree in 1963, all from the University ofFlorida, Gainesville.

While completing graduate studies he worked on development of a C-band linear ac-celerator. This effort included design of pulse modulators, and RF drive chain, and atraveling wave structure and analysis of three-dimensional relativistic electron trajectories.For the last 14 years he has worked for Martin Marietta Corporation, Denver, Colo. Heanalyzed nuclear electromagnetic pulse (EMP) excitation mechanisms and the suscep-tibilities of missile launch facilities and missiles in flight and developed EMP testequipment. He also analyzed the susceptibilities of various weapon systems to nuclearradiation and devised hardening techniques. In 1969 he began working on NASA pro-grams with definitions of experiments for advanced space missions, including space sta-tion, lunar orbiter missions, and the Apollo/Soyez test program. During 1971 he managedthe Martin Marietta experiment definition task on the modular space station. He wasProject Engineer for a group performing experiment-related analyses for the Viking pro-gram. After design and breadboarding of critical subsystems for the planetary radioastronomy receiver (PRAR) he was Chief Engineer on the PRAR program. In this positionhe supervised PRAR construction and testing activity and was directly involved in RFcircuit design and testing tasks. He is now investigating spectrum analyzer designs foradvanced planetary radio astronomy and defense system applications.

Dr. Lang is a member of Phi Kappa Phi, Sigma Tau, and Tau Beta Pi.

Robert G. Peltzer (M'61) was born in New Britain, Conn., in 1931. He received theB.S.E.E. degree in 1957 from the University of Connecticut and the M.S.E.E. degree in1961 from the University of Michigan.

From 1957 to 1962 he was an Assistant Engineer at the Bendix Systems Division,Ann Arbor, Mich., where he participated in the solution of system design problems in-volving radar, acoustics, electrostatic suspension, and meteorology. He was also responsi-ble for the research and development and field testing of a doppler detection system foraircraft. In 1962 he joined the Radio Astronomy Laboratory, University of Michigan, to

participate in the development of instruments for low-frequency space radio astronomyas OGO-I and III Project Engineer, OGO Projects Group Head, IMP-I Project Managerand Engineer, and Associate Director of the Laboratory. During this time he was re-

sponsible for instrument development, technical subcontracts monitoring, calibration,test and integration on spacecraft, and evaluation of performance during the missions,particularly for removal of instrumental effects for science data analysis. In addition,he developed data presentation specifications and served as EMC advisor to the space-craft contractors for interference reduction. From 1971 to 1973 he was the technicaladvisor and instrument design leader for the MJS 77 Planetary Radio Astronomy Ex-periment Team. In 1973 he joined the Astro-Geophysics Department, University ofColorado, Boulder, as MJS 77 Project Engineer, where he is responsible for instrumentspecifications, technical performance of subcontractors, spacecraft integration, and

mission performance evaluation for removal of instrumental effects for science dataanalysis. In addition, he serves as advisor to the Radio Astronomy Observatory and as

EMC advisor to JPL and coexperimenters on MJS 77.Mr. Peltzer is a member of Sigma Xi, Tau Beta Pi, Eta Kappa Nu, and Phi Kappa Phi.

47IE.E TRANSACTIONS ON AEROSPACE AND ELECTRONIC SYSTEMS VOL. AES-13, NO. 5 SEPTEMBER 1977472