Satgen 253 Satellite Spotters Part 2 by GM4IHJ 29th Jan 94 BID of this msg is SGEN253 Please use this BID if you retransmit this msg Part 1 suggested the general headings, and went on to discuss the importance of frequency , in classifying possible satellite signals. The next feature of importance is the Mode of transmission or modulation of the strange signal . This can be any one of 8 general types. CONTINUOUS CARRIER Radio Amateurs are required by law to transmit their callsign regularly. But very few if any military or commercial satellites do this. Indeed many of them transmit nothing but a continuous carrier wave totally unmodulated. Which is not as useless as it may seem when you realise this type of signal is best for investigating any of the following :- Propagation, Faraday, Scintillation, Aurora,and, Doppler studies. Typical satellites of this type are put up by American Universities and Military, often in the 430 to 440 MHz Amateur Band. INTERUPTED CARRIER Only Amateur radio satellites send morse code, but some older Russian sats use Pulse Count or Pulse Width modulation. These latter sound like slow morse with odd length dots. RTTY is used by Mir and it can also be heard from the Transit and Cosnav Navsats around 150 MHz. The navsat RTTY sends sat orbit data. But on the concurrent 400 MHz transmiter they usually send only Continuous Carrier. DIGITAL Most modern satellites and deep space craft use digital communications and telemetry. Typical modulations are PSK (as in Amateur Pacsats), or, FSK ( as in Uosats and Korean sats). whilst most commercial comsats use QPSK . Marisats and Intel geosats sometimes alternate QPSK and Voice, on each of their many separate channels. Speeds are usual 1200bps for PSK, 2400 bps for QPSK and 9600 bps for FSK. Some Deep space probes can use 32 and 64 Kbps for picture traffic but can revert to 100 bps or 200 bps when the path is a bad one or main antennas fail. VOICE Clear voice traffic can be heard from geosats. Indeed voice is often used to establish the call to a distant receiver before switching to QPSK to pass traffic. SPREAD SPECTRUM This uses modulation by, pseudo randomly generated noise. The American GPS Navsats all transmit on the same frequency but each transmission has its own noise code which your receiver has to use to separate it from all the other signals. By contrast the equivalent Russian GLOSNAV sats use a different frequency for each sat , which means their wide band pseudo random noise covers many MHz and is reputed to cause problems for Radio Astronomers on nearby frequencies. PLEASE NOTE that neither Spread Spectrum or Digital 9600 bps signals can be heard by "ear ". Your ear cannot separate the real, and the pseudo random noise. So you have to have a receiver with AFC or a centre tuning FM meter to tune them in. WEFAX Weather reporting satellites of the NOAA and Meteor types (136 to 138 MHz ) use a simple fax type picture transmission which is easily identified. Its just like the Swish, Swish of a car windscreen wiper. TELEVISION There are a multitude of different TV formats in use from satellites. Most of those below 1000 MHz use American NTSC format which has a different line number than PAL or SECAM and needs line hold adjustment to lock a picture. Geosats around 3GHz and 10GHz can mostly be translated electronically to PAL or SECAM, but remember please that more than half of them are scrambled and need a decoder. Special note HF prop RS10 and RS12 has been superb 23 to 28 Jan DJ8DT monitored RS10 as it overflew Antarctica on 25 Jan. 73 de GM4IHJ@GB7SAN