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"AO-7" redirects here. For other uses, see AO-7 (disambiguation).
Image Of The Satellite Amsat-OSCAR 7
Mission type Amateur Radio Satellite
Operator AMSAT
COSPAR ID 1974-089B
SATCAT № 7530
Website Amsat.Org
Mission duration 42 years, 1 month and 9 days elapsed
Spacecraft properties
Launch mass 28.8 kilograms (63 lb)
Dimensions 36.0cm x 42.4cm octahedron
Start of mission
Launch date 15 November 1974 (1974-11-15)
Rocket Delta 2310
Launch site Vandenberg SLC-2W
Orbital parameters
Reference system Geocentric
Regime Low Earth
Perigee 1,447.5 kilometers (899 Mi)
Apogee 1,465.6 kilometers (910 Mi)
Inclination 101.59 degrees
Period 114.9 Minutes

AO-7 (aka AMSAT-OSCAR 7) is the second Phase 2 amateur radio satellite constructed by AMSAT-NA, and it was launched into Low Earth Orbit on November 15, 1974. It remained operational until a battery failure in 1981. Then after 21 years of silence, the satellite was heard again on June 21, 2002 — 27 years after launch.

AO-7 is the oldest amateur satellite still in use, and is one of the oldest operational communications satellites. It carries two amateur radio transponders. Its "Mode A" transponder has an uplink on the 2-meter band and a downlink on the 10-meter band. The "Mode B" transponder has an uplink on the 70-centimeter band and a downlink on the 2-meter band. AMSAT-OSCAR 7 also carries four beacons which are designed to operate on the 10 meter, 2 meter, 70 centimeter and 13-centimeter bands. The 13 cm beacon was never activated due to a change in international treaties.[1]

AMSAT reported AO-7 still operational on June 25, 2015, with reliable power only from its solar panels; the report stated the cause of the 21-year outage was a short circuit in the battery and the restoration of service was due to its becoming an open circuit. The satellite eclipses on every orbit during the northern summer and autumn; the rest of the year it is in continuous sunlight and alternates between transmission modes A and B. All transponders and beacons are operational.[2]


AO-7 was the second Phase 2 satellite (Phase II-B). It weighs 28.6 kg (63 Pounds). AO-7's is in a 1444 x 1459 km high orbit. It is Octahedrally shaped 360 mm high and 424 mm in diameter. AO-7 has a Circularly polarized canted turnstile VHF/UHF antenna system and HF dipole. Four radio masts mounted at 90 degree intervals on the base of the satellite 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. AO-7 has Redundant command decoders of a design similar to the unit proven highly successful in OSCAR 6 were flown. The decoder has provisions for 35 separate functions, and is designed to provide a reliable means of controlling the emissions of the repeaters, beacons and other experiments aboard the spacecraft.


AO-7 demonstrated several uses of new technologies and operations [3]

  • First satellite-to-satellite relay, through AO-6.[4]
  • Early demonstrations of low-budget medical data relay and Doppler location of ground transmitters for search-and-rescue operations were carried out using this satellite.
  • The Mode-B transponder was the first using "HELAPS" (High Efficient Linear Amplification by Parametric Synthesis) technology developed by Dr. Karl Meinzer as part of his Ph.D.
  • First to fly a battery charge regulator (BCR).

Legal issues[edit]

The uplink frequency predates the WARC 1979 allocation of 435-438 MHz by the ITU for the Amateur Satellite Service which places the uplink in the 70cm weak signal segment. Additionally, the IARU bandplan has the 432.1 MHz range (which is used for mode B uplink) marked for "weak signal" in all three Regions. Accessing the Mode B uplink is permitted in the United States under a waiver from the FCC.[5]

Current status[edit]

As of December 2015, contacts with AO-7 are reported daily.[6]

See also[edit]


  1. ^ "ARRLWeb: It's Aliiiiive! AMSAT-OSCAR 7 Satellite Returns from the Dead". American Radio Relay League. 24 June 2006. Archived from the original on 4 November 2005. Retrieved 26 September 2010. 
  2. ^ "AMSAT - Satellite Detail - AMSAT-OSCAR 7". AMSAT. 6 April 2006. Retrieved 1 March 2008. 
  3. ^ "AMSAT-OSCAR 7 Satellite Summary". AMSAT. 31 May 2003. Archived from the original on 21 December 2009. Retrieved 16 December 2009. 
  4. ^ Klein, Perry (October 1975). "Intersatellite communication using the AMSAT-OSCAR 6 and AMSAT-OSCAR 7 radio amateur satellites". IEEE. Retrieved 16 December 2009. 
  5. ^
  6. ^ Carr, David; Bruninga, Bob (12 November 2012). "OSCAR Satellite Status page by KD5QGR". Retrieved 15 February 2015.