Satgen379    Microwave Sat Voice     by GM4IHJ              29 June 96

   Satgen378 discussing the Picosat concept of using ACSSB on mode L
LEO satellites, has produced a flurry of interesting correspondence,
regarding the future of amateur satellite real time voice qsos, now
that the lower frequency bands are becoming untenable for satellite
users. What other options are available for voice modes on microwave
satellites?

a. Firstly we must differentiate between LEO sats in low earth orbit
and Molniya sats in high altitude orbits. With LEO sats Tx power can
be minimal but doppler shift is very high indeed and posses severe
problems. By contrast the high altitude satellite orbits offer no
great doppler shift problems, but they do require high power
tramsmitters , low noise receivers and trainable directional high gain
antennas with elevation as well as azimuth rotation capability.

b. So Phase 3 high altitude Molniya satellites can be used for mode S
voice, albeit at considerable complexity and expense, in respect of
ground station equipment.

c. By contrast LEO sats can use simple antennas and hand portable low
power equipment available at relatively low cost, provided that some
way is found to beat the problem of the high rates of tuning necessary
to follow the very large doppler shift of the signal.

Phase 3 is expensive . We will get only one and only the more affluent
radio amateurs will be able to use it. So what do the rest do ? What
is clear from correspondence is that most amsat operators ( as opposed
to builders ) want real time voice qsos , not soulless, keyboard to
keyboard, time delayed, impersonal, digital exchanges of messages. 

Picosat will provide some of the answers to this dilemma, but it is
not the only answer. We could go digital . Given the plethora of
equipment for commercial digital voice personal mobile communications
now coming forward, it should not be impossible for amsat builders to
develope existing commercial hardware components suitable for ground
station ( mobile or fixed ) operation using digital voice repeaters
aboard channelised microsats, in LEO orbits. 

Given an Amsat LEO Digital voice microsat building program, we might
even be able to make good the unfulfilled boast of a former Amsat
spokesman , who suggested that Phase 3 would provide the equivalent of
a new 20metre band in the sky. If we can produce 17 or so store and
forward sats in 6 or 7 years, surely we can repeat the process with
more attractive digital voice sats in roughly the same time period, in
spite of what will clearly be a period of financial stringency
consequent on the enormous cost of Phase 3D. With a fleet of readily
usable , simple to access voice qso satellites, we may even be able to
attract more members to Amsat. Equally important, would be amsat
builders will be able to test themselves against a real challenge
rather than producing yet more clones of a store and forward type,
that has been around for 10 years, and which now appear to be losing
most of their former users, in what seems to be, a mass migration to
the Internet.