I've been thinking about how the use of mode UV might change with a geostationary satellite. It could allow for the use of very simple antennas for mobile operation as was done with AO-16. Since the satellite is stabilized and fairly large, it may be possible for AMSAT to procure space for a broadside array with at least 2 elements on 2 meters with vertical polarization. This would give 8 or 9 dBi of gain and be compatible with 1/4-wavelength whip antennas mounted on automobiles in mid-latitude locations. It would also allow the speed of the currently planned digital uplinks and downlink to be increased.
This digital downlink could allow multi-user digital voice operation with fairly low power given that 2400 and 1200 bps MELP vocoders are now available. 50 kHz could allocated for SSB and 50 kHz for a TDM digital downlink. A 24 kBaud QPSK downlink could handle 10-20 users using a rate 1/2 error correcting code. If we assume that the man-made noise level is 6 dB above the thermal noise level, a 1 dB NF LNA, 6 dB SNR and a 32 kHz bandwidth for the downlink signal, -116 dBm is required at the receiver. Path loss is 168 dB, so at least 52 dBm EIRP is required from the satellite which means 20-25 W of transmitter output. This seems feasible for the HELAPS transmiter or there could be a separate transmitter and a high-level power combiner.
Both 70-cm analog and digital uplinks could be handled by a common receiver using a short (1 m) yagi antenna or a broadside array.
73,
John KD6OZH