Satgen341  Satellite Software Pt8   by GM4IHJ                7th Oct 95

TELEMETRY DECODING SOFTWARE. All Amateur radio satellites transmit
downlink messages which report the state of the satellites onboard
components and sensors, and some satellites also report details of their
external environment. Difficulty number one is that before you can decode
this telemetry, you have to be able to receive and demodulate it, and
there are AT LEAST 8 different forms of modulation in use.
Telemetry Modulation type        Satellites using this mode
1.  CW                           AO13,RS10/11, RS12/13,RS15,LO19,FO20
2.  RTTY                         AO13
3.  PSK 400 bps                  AO13
4.  AFSK 1200 bps packet         DO17
5.  AFSK 1200 bps ASCII          UO11
6.  PSK  1200 bps packet         AO16,WO18,LO19,FO20
7.  AFSK 9600 bps ASCII          Uo22, Kit23, Kit25
8.  Digitized Speech             Uo11

If you have suitable modems and modem protocol software ( Packcom ,
procomm etc), you can capture all the above automatic telegraphy modes ( 2
to 7 ) and store them as data blocks on your computer. Satellites using CW
or digitised speech are a different proposition . Few stations have
automatic CW capture and translation to ASCII, particularly where the
satellite in question uses a 29 MHz downlink with its frequent fading due
to Faraday polarisation rotation and , multipath reception. So manual
aural copy of CW is the norm , whereas digitised speech can be tape
recorded without any translation being necessary, but it must then like
the CW be converted to ASCII files on a word processor.

Once the telemetry data is in a word processor ASCII file or , has been
demodulated into ASCII output, it can then be decoded automatically if
suitable telemetry parameter decode software is available. Amsat NA supply
program TLMDII for decoding Pacsat telemetry ( AO16 to AO19), and they
also supply a program for decoding AO13 PSK telemetry files. But there is
not a lot more software for PC users and even less is available for Mac
users. A situation which is only to be expected , because most of the
other satellites have highly individual types of telemetry files , each of
which requires its own unique decode software.

At IHJ this impasse has been partially resolved by writing simple GWBASIC
decode programs for specific small blocks of individual satellite
telemetry rather than attempt to translate the whole telemetry file, much
of which is surplus to the experiments being followed :- Eg
For AO16 to AO19 only the important solar panel current files are decoded.
For RS12 and RS15 only voltage readings are required. Indeed in some cases
just one reading is required from the satellite , as may perhaps be the
case in the next year or so when all that many users will be interested in
are RS15 power supply readings as it goes into and out of solar eclipse,
and AO13 temperature readings if as anticipated it drops lower in perigee
and heats up as it encounters the thicker low altitude atmosphere.