Operators of the GB3ZZ amateur television repeater station
The indoor box of a satellite installation is a receiver in it's own right. The dish end of things is responsible for shifting the extremely high frequencies in the satellite band down to a more manageable range which the box can then convert back to sound and pictures. Conveniently for us, the most popular ATV band is more or less central in the tuning range of the box. What we do is forget everything at the dish and simply connect a suitable antenna directly to the end of the dish cable.
A word of warning ! All the electronics at the dish has to be powered from somewhere and to save money, manufacturers use the cable carrying the signals down from the LNB to carry power up to it as well. We can easily get into trouble here because most antennas will short out the power and damage the receiver box. Fortunately, there is a very simple and inexpensive fix for this, all that's needed is one small capacitor. Capacitors have the property of allowing signals to pass through them while holding back DC power. We can use one to isolate the power from the short circuit while still letting signals pass though and down the cable. The capacitor is wired in-line with the inner wire of the cable, one end to the inner wire, the other to the terminal the wire used to go to. The value of the capacitor should be 100 pF (pico Farrads) and it should be rated to withstand 30 volts or more. The best type to use is made from ceramic materials. Most of the ones available with this value will be made from ceramic and will be suitable. There is usually plenty of room in the plastic junction box on the antenna to house it but keep it's wires as short as you can !
If the antenna is pointing at a repeater or someone's transmitter you should be able to pick them up at this stage - if you know which frequency they are on. Tuning in can be a problem at first but there is an easy way of doing it when you know how. Almost all receivers will tell you the frequency of the satellite channel they are tuned to. Sometimes this is shown on the front of the receiver, sometimes on the screen and sometimes you have to find it in the tuning or setup menu. The figures will look something like '11035 Mhz' or '11.035 Ghz' but the actual numbers depend on the tuning itself. Unfortunately, these are the satellite frequencies, not the ones the receiver box is tuned to. The difference arises because the LNB at the dish normally shifts the band downwards and being rather dumb bits of equipment, the receiver doesn't know the LNB isn't there any longer so it still compensates the display by the amount of the shift. We can reverse the math to find out the real frequency by subtracting the shift from the figures shown. Usually you have to subtract 9,750 or 10,600 but you will have to experiment to find out which - it depends on the LNB that was being used.
A word of warning ! All the electronics at the dish has to be powered from somewhere and to save money, manufacturers use the cable carrying the signals down from the LNB to carry power up to it as well. We can easily get into trouble here because most antennas will short out the power and damage the receiver box. Fortunately, there is a very simple and inexpensive fix for this, all that's needed is one small capacitor. Capacitors have the property of allowing signals to pass through them while holding back DC power. We can use one to isolate the power from the short circuit while still letting signals pass though and down the cable. The capacitor is wired in-line with the inner wire of the cable, one end to the inner wire, the other to the terminal the wire used to go to. The value of the capacitor should be 100 pF (pico Farrads) and it should be rated to withstand 30 volts or more. The best type to use is made from ceramic materials. Most of the ones available with this value will be made from ceramic and will be suitable. There is usually plenty of room in the plastic junction box on the antenna to house it but keep it's wires as short as you can !
If the antenna is pointing at a repeater or someone's transmitter you should be able to pick them up at this stage - if you know which frequency they are on. Tuning in can be a problem at first but there is an easy way of doing it when you know how. Almost all receivers will tell you the frequency of the satellite channel they are tuned to. Sometimes this is shown on the front of the receiver, sometimes on the screen and sometimes you have to find it in the tuning or setup menu. The figures will look something like '11035 Mhz' or '11.035 Ghz' but the actual numbers depend on the tuning itself. Unfortunately, these are the satellite frequencies, not the ones the receiver box is tuned to. The difference arises because the LNB at the dish normally shifts the band downwards and being rather dumb bits of equipment, the receiver doesn't know the LNB isn't there any longer so it still compensates the display by the amount of the shift. We can reverse the math to find out the real frequency by subtracting the shift from the figures shown. Usually you have to subtract 9,750 or 10,600 but you will have to experiment to find out which - it depends on the LNB that was being used.