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fahnen/9.jpg Amateur Satellite Summary - AO-7
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AMSAT-OSCAR 7

Satellite Summary

Name: AMSAT-OSCAR 7 (Phase-IIB)
Nasa Catalog Number:7530
Launched: November 15, 1974
Launch vehicle: Delta 2310
Launched piggyback with: ITOS-G (NOAA 4) and the Spanish INTASAT
Launch location: Vandenberg Air Force Base, Lompoc, California
Weight: 28.6 kg
Orbit: 1444 x 1459 km
Inclination: Inclination 101.7 degrees
Period:  
Size: Octahedral shaped 360 mm high and 424 mm in diameter
Modes: A, B, and C

Beacons:

  • 29.502 MHz (200 mw) Used in conjunction with Mode A
  • 145.972 MHz (200 mw) Used in conjunction with Mode B and C [low power Mode B]
  • 435.100 MHz (intermittent problem -- switches between 400 mw and 10 mw)
  • 2304.1 MHz (40 mw) Must be commanded on. Auto off after 15 minutes. Requires STA to operate.
Linear Transponders:
  • Transponder I: Mode A
    • Type: linear, non-inverting
    • Uplink: 145.850 - 145.950 MHz
    • Downlink: 29.400 - 29.500 MHz
    • Translation Equation: 
          Downlink (MHz) = Uplink (MHz) - 116.450 MHz +/- Doppler 
    • Output Power: 1.3 watts PEP (start of life)
  • Transponder II: Mode B and Mode C (low power) 
    • Type: linear, inverting
    • Uplink: 432.125 - 432.175 MHz *See Note
    • Downlink: 145.975 - 145.925 MHz
    • Translation Equation: 
          Downlink (MHz) = 578.100 - uplink (MHz) +/- Doppler
    • Output Power: 8 watts PEP Mode B (start of life), 2.5 watts PEP Mode C

*Note: Due to changes in Amateur Service and Amateur Satellite Service there are questions as to legality of Amateurs transmitting to AO-7. The uplink frequency predates the WARC '79 allocation of 435-438 MHz by the ITU for the Amateur Satellite Service and places the uplink in 70cm weak signal segment.

Potential users should realize that when they are uplinking to a satellite, they are no longer operating in the Amateur Service but instead operating in the Amateur Satellite Service. Thus they are subject to Amateur Satellite Service rules. Therefore uplinking to AO-7 is possibly illegal since the Amateur Satellite Service is not permitted at 432.1 MHz. Also, since the IARU bandplan has the 432.1 MHz range earmarked as "weak signal" in all three Regions, it would appear that all users trying to access the uplink are also outside the Amateur Satellite Service rules and regulations.

Firsts:
  • Satellite-to-satellite relay communication via AO-6.
  • Early demonstrations of low-budget medical data relay and Doppler location of ground transmitters for search-and-rescue operations were done using this satellite.
  • The Mode-B transponder was the first using "HELAPS" (High Efficient Linear Amplification by Parametric Synthesis) technology was developed by Dr. Karl Meinzer as part of his Ph.D.
  • First to fly a Battery Charge Regulator (BCR).
Status: Semi-Operational
  • The latest information is available from:
  • Jan King, W3GEY reports AO-7 is almost certainly running only off the solar panels. It is very likely to be on only when in the sun and off in eclipse. Therefore, AO-7 will reset each orbit and may not turn on each time.

Telemetry:


Description

AMSAT-OSCAR 7 was launched November 15, 1974 by a Delta 2310 launcher from Vandenberg Air Force Base, Lompoc, California. AO-7 was launched piggyback with ITOS-G (NOAA 4) and the Spanish INTASAT. The second phase 2 satellite (Phase II-B). Weight 28.6 kg. Orbit 1444 x 1459 km. Inclination 101.7 degrees. Octahedrally shaped 360 mm high and 424 mm in diameter. Circularly polarized canted turnstile VHF/UHF antenna system and HF dipole.

Similar to AO-6. Built by a multi-national (German, Canadian, United States, and Australian) team of radio amateurs under the direction of AMSAT-NA. It carried Mode A (145.850-950 MHz uplink and 29.400-500 MHz downlink) and Mode B (432.180-120 MHz uplink and 145.920-980 MHz downlink (inverted)) linear transponders and 29.500 and 145.700 MHz beacons. The 2304.1 MHz was never turned on because of international treaty constraints. 

Four radio masts mounted at 90 degree intervals on the base and two experimental repeater systems provided store-and-forward for morse and teletype messages (Codestore) as it orbited around the world. The Mode-B transponder was designed and build by Karl Meinzer, DJ4ZC and Werner Haas, DJ5KQ. The Mode-B transponder was the first using "HELAPS" (High Efficient Linear Amplification by Parametric Synthesis) technology was developed by Dr. Karl Meinzer as part of his Ph.D. 

Additional information about AO-7 was printed in the September 1974 AMSAT Newsletter.

AO-7 was operational for 6.5 years until a battery failure ceased operation in mid 1981.  Then on June 21, 2002, Pat Gowen, G3IOR, posted this email message on AMSAT-BB:

From: "pat gowen" <patgowen@btconnect.com>
To: <amsat-bb@AMSAT.Org>
Subject: [amsat-bb] Re: Lazarus?
Date: Fri, 21 Jun 2002 22:30:54 +0100

I have just come across something most remarkable this Friday 21st June evening. Checking out interlopers in our 145.800 - 146.000 MHz space band with a new vertical now atop my 60' tower and working like magic, at 1728 UTC I came across a beacon at S.7 sending slow 8 -10 wpm CW on 145.973.8 MHz. It slowly Dopplered down to 145.970 MHz before going out at 1739 UTC. A full run of TLM went: -

Hi Hi
100 176 164 178
280 262 200 254
375 358 331 354
453 454 461 459
541 501 552 529
600 600 601 651
Hi Hi

It sounded VERY familiar, but, I'm dammned if I can recall which one it was. Obviously an OSCAR, but which had the callsign W3OHI? Oscar-6, 7 or 8? I think it was OSCAR-6. If so, we have a new longevity record, even beating RS-1!

The beacon peaked S9 and there were S7 burbles some 10 - 20 KHz below the beacon, FSK'ing slightly as the beacon keyed. At times the beacon took on a rough quality, wobbling in frequency, then coming back strong and quite stable again. Going by the QSB rate it had about a 1 minute spin.

Could any veteran keen observers (who might look for it) please tell me what it was, as I feel sure that any old time AMSAT OSCAR devotee may have a far better memory than I!

73, Pat, G3IOR

Jan King, W3GEY, the AMSAT-OSCAR-7 Project Manager commented:

[AO-7] has a good set of arrays and the first BCR (battery charge regulator) we ever flew. It's the first spacecraft we ever had that was capable of overcharging the battery. When the battery failed the cells began to fail short. One cell after another failed and the voltage measured on telemetry began to drop. So, the cells were clearly failing SHORT. Now, after all these years, what happens if any one of the cells loses the short and becomes open? Then, the entire power bus becomes unclamped from ground and the spacecraft loads begin to again be powered but, this time only from the arrays. Now you have a daytime only satellite but, each time the sun rises at the spacecraft you have a random generator that either turns on Mode A or Mode B or whatever it wants. So, occasionally that 70cm/2m transponder transmitter and beacon must least work. From what you have told me (and without going back and decoding the old telemetry equations) I can tell you that the following things work in that spacecraft: The arrays, the BCR, the ISR (instrumentation switching regulator), the Mode B transmitter and beacon injection circuitry, the Morse Code telemetry encoder, and the voltage reference circuitry. The latter I know is working because the last telemetry value is 651. The "6" is just the row number of the telemetry value but the 51 means that the 1/2 volt reference is measuring 0.51 volts. I know that telemetry equation by heart since it was used as the calibration value for the rest of the telemetry system. So the telemetry has a fair chance of being decoded and making some sense!!! .  

The full text of W3GEY's comments are here.

Initial reports on the health of AO-7 are:

  • Telemetry received may be good or bad. You can determine if the telemetry is good by the 6D value. It is the reference voltage for the analog TLM system and it should be around 50. If not, then the remainder of the telemetry will be incorrect.
  • Jan King, W3GEY notes that AO-7 had (has?) a very sensitive receiver and a good uplink antenna. 5 watts EIRP should provide a good downlink. Amplifiers are not required for the uplink. 
  • Excessive uplink power may be cause FMing of the transponder and may be causing the input voltage to the regulator that provides 6D to fluctuate causing all telemetry to be bad.
  • AO-7 is almost certainly running only off the solar panels. It is very likely to be on only when in the sun and off in eclipse. Since it is resetting each orbit it may not come on every time. Reports of hearing the beacon just as it comes out of eclipse would be particularly interesting.

 


References

  • Joe Kasser G3ZCZ/W3 and Jan King W3GEY, "OSCAR 7 and Its Capabilities,"QST, Feb 1974, p. 56-60.
  • "OSCAR News: OSCAR 7",QST, Nov 1974, p. 81.
  • David Sumner, K1ZND, "OSCAR News: OSCAR 7 - It Works!,"QST, Jan 1975, p. 49.
  • "OSCAR News: Reading the OSCAR 7 Telemetry",QST, Feb 1975, p. 63.
  • Perry Klein and Ray Soifer, W2RS, "Intersatellite Communication Using the AMSAT-OSCAR 6 and AMSAT-OSCAR 7 Radio Amateur Satellites,"Proceedings of the IEEE Letters, Oct 1975, pp 1526-1527.
  • D. Brandel, P. Schmidt, and B. Trudell, "Improvements in Search and Rescue Distress Alerting and Location Using Satellites,"IEEE WESCON, Sep 1976.
  • J. Kleinman, "OSCAR Medical Data,"QST, Oct 1976, pp 42-43.
  • D. Nelson, "Medical Relay by Satellite,"Ham Radio, Apr 1977, pp 67-73.
  • Martin Davidoff, "Predicting Close Encounters: OSCAR 7 and OSCAR 8,"Ham Radio, Vol. 12, No. 7, Jul 1979, pp 62-67.
  • "Technical Correspondence: A Look at OSCAR-7 Telemetry",QST, Jul 1980, p. 38.

Credits: Thanks G3IOR, WD0E, W3GEY, DB2OS, W3IWI.

Last update May 31, 2003 - N7HPR


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