SATELLITE BASICS
The very first thing that one must learn about satellite operating is that one should NEVER have a signal stronger than the beacon.
The beacon is your reference, remember ... the available power from the batteries is distributed across the passband allowing several users at the same time. Using too much power means you're ‘stealing’ power from the other users of the transponder, apart from which, antisocial behaviour of that kind has no place in satellite operating.
ALWAYS tune to the beacon frequency first and adjust your power accordingly.
Get into that habit right from day one and don't ever become an ALLIGATOR. This is the single worst thing you can ever do to your fellow satellite users.
Operating satellites is not too different from terrestrial communications.
There are however two subtle differences .....
1) Full Duplex
2) Doppler Effect.
Full Duplex.
Unlike terrestrial operating where each operator must take his/her turn to
speak into the microphone due to both stations being on the same frequency for both transmit and receive ... (semi-duplex) ... satellite operating is different in that the operator transmits on one frequency and receives on a different frequency ... usually on different bands ...... which means that everyone can transmit and receive at the same time ... just like a telephone conversation. The main advantage of this is that everyone can hear everyone else ... (i.e. no excuse for QRM!).
Doppler effect.
Everyone has experienced Doppler effect ... perhaps without realising it.
Imagine a motor car approaching you, the sound of the engine has a certain pitch or frequency ... as the car passes then recedes, the tone of the engine sounds lower in pitch. If on the other hand you were moving parallel to the motor car, at the same speed, the sound of the engine would remain at the same pitch. You have now learned the basics of Doppler effect.
When a satellite is moving towards you the frequency is HIGHER than the nominal beacon frequency and when it's moving away from you the frequency is LOWER than the nominal beacon frequency. The rate of Doppler shift depends primarily on the frequency in use. For low earth orbit satellites at a height of about 1000Km the rate is approximately:
28MHz.........plus/minus 4-7khz
145MHz.......plus/minus 8-10khz
435MHz.......plus/minus 16-20khz
1300MHz.....plus/minus 40-60khz
2400mhz.......plus/minus 80-100khz
Note - the higher the frequency, the higher is the rate of Doppler shift.
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Example Doppler curve.
The above Doppler curve was of the now defunct Oscar 7 satellite transmitting in the 2 metre amateur band.
There are two prime tuning conventions for Doppler, one American and one European. As can be seen from the above table, the higher frequencies have the most Doppler ... therefore it's logical that one ‘adjusts’ the higher of the two frequencies used.
That is to say .... imagine you're transmitting on 145MHz and receiving on 435MHz ... in this case you should keep the transmitter FIXED on 145MHz and ADJUST the receiver on 435MHz. This is the American convention.
In Europe it has become a ‘habit’... (due to Mode B operating on Oscars 10 and 13) ... to tune the transmitter regardless ..... we believe the American convention will become the working standard.