[amsat-bb] Digital sats with less

Gould Smith gouldsmi@bellsouth.net
Thu Aug 31 09:49:44 PDT 2006

Hello All,

While re-configuring my digital station the last couple of weeks I have had the opportunity to try some things I normally wouldn't.  I was surprised the last couple of days to find that I could work GO-32 with less that I expected.

I encourage you all to try 9600 Digital satellite operation.  GO-32 transmits with about 1W of power and is fairly easy to receive and decode.  

My minimal system is: inexpensive, 10 element 70cm yagi (Diamond A430S10); no preamp; 50 feet Flex 4XL coax; FT-847; MFJ 1270C with added 9600 bps modem board; WiSP Pacsat protocol software; 15 W into 50 feet of LMR400 coax; 4 element, 2M yagi (M2 2M4).  Antennas are mounted at a fixed 25 degree angle, AZ only rotor.
Setting all this up and getting it operational isn't trivial as you have to have a number of things that all must work together, but certainly do-able and a good challenge to get a digital station operational.  Now I always recommend a preamp for digital operation, and I only decoded about 1/3-1/2 of the digital data I usually get using the same system with a preamp.  When AO-51 is in digital mode and transmitting at 300mW, you need the preamp.

 1) Use the 145.890 uplink frequency for GO-32, SatPC32 defaults to the 145.850 uplink and I couldn't get that one to work
 2) There is no telemetry data from GO-32
 3) AO-51 will be in digital mode again Sep 18, so get operational on GO-32 and ready to get telemetry data from AO-51
 4) You can use a soundcard 9600 bps software decoder, but must have a way to send the decoded data into a serial port (or USB to serial) to make much sense of it.  TlmECHO or WiSP will do the protocol conversion.
 5) TlmECHO program is a good program to start with, it will show the digital data (even GO-32), without having to do a major setup as with WiSP, plus you will be ready to get the AO-51 telemetry
6) DCD led on does not mean that you are correctly decoding the data, just that you are receiving a signal.  These data packets are all or nothing, if your modem misreads 1 bit out of a packet the entire packet is trashed.
7) Keep the signal centered (Doppler correction), if your radio has a Discriminator meter just keep the signal centered.  I notice quite a data drop when the Discriminator reading is a bar or two off center.
8) I wouldn't recommend using anything other than a small, tracking beam for receiving 9600 bps digital signals

Gould, WA4SXM

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