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WG3K   > ANS      16.11.24 01:42l 34 Lines 1761 Bytes #53 (0) @ AMSAT
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Subj: Celebrating AO-7: First Earth-Space-Space-Earth Relay Commun
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Sent: 241116/0034Z 10014@WG3K.#SMD.MD.USA.NOAM LinBPQ6.0.24


As AO-7, launched on November 15, 1974, approaches is 50th Anniversary and
setting a record as the longest operating satellite, we look back at a few
of its noteworthy accomplishments.

The downlink spectrum of AO-7â€Ös UHF/VHF transponder overlapped with AO-6â€Ös
VHF-to-HF transponder. The overlap of the two was approximately 50 kHz
wide. The two orbits were the same - almost. AO-7â€Ös mean motion was
slightly higher than that of AO-6, which means, once every year of so, AO-6
will “lap� its younger sibling in space. During the time when the two
spacecraft are in closer proximity, it was already known to be
theoretically possible (if AO-7 has its UHF/VHF transponder on) for one
user to communicate through two spacecraft in succession, with the downlink
of AO-7â€Ös transponder being relayed through AO-6â€Ös VHF/HF transponder
uplink, and then, with the doubly relayed signal arriving on 29.5 MHz to
another user on the ground. This could be done, in certain geometries, in
both directions, making a two-way double-hop communications possible.

The first successful Earth-Space-Space-Earth relay of this type took place
on January 6, 1975. This happened early in AO-7â€Ös  “firstâ€� lifetime and
during the first occasion when AO-6 approached AO-7, in their very similar
orbits. The two stations were both located in the state of Texas – one in
Dallas and one in Richardson. This method of communications was also
conducted and reported by 55 other user stations from 12 countries during
1975. These events were documented in the IEEE Proceedings in October of
1975.

See another AO-7 50 Year Anniversary highlight in next weekâ€Ös ANS Weekly
Bulletin.

*[ANS thanks Jan King, W3GEY, AMSAT AO-7  Project Manager for the above
information]*



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