SatSig topic:

C band Interference

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Jul 8^th, 2008 at 8:11am

Hello all. Since some time we face a problem of interference on our site.
our connection is cut regularly and we can not exploit it.
when the provider cut its carrier, there is another carrier that appears from time to time at the same place on our spectrum analyser.
how can we determine the source of this interference? and how to solve this problem?
Regards

Jul 15^th, 2008 at 8:52am

you first capture the interference spectrum plot. Then send it over to the satellite operator and request them to find out who generate the interference. if they cannot solve it, you need to request them to allocate another freq. slot.

Good Luck.

Jul 15^th, 2008 at 10:22am

Once you have recorded the characteristics of the interference try also to find its source yourself.

Cross-pol, adjacent satellite and spurious signals are possibilities.

Does looking on the other polarisation show a very strong carrier that matches the interference ? If so, your interference problem may be due to poor polarisation setting at your dish or at the uplink dish for that carrier. If you are using circular polarisation there is no adjustment possible; your feed should work well if it is not part full of water, nut in the waveguide etc.

Does repointing your dish towards adjacent satellites either side show that the interferer is a carrier on an adjacent satellite ? If so, the problem may be poor sidelobe on your dish or poor sidelobe on the uplink dish for that carrier. Is your dish rim flat and the focus correct?.

You say the interference appears from time to time. It would be useful to tell the satellite operator just when it starts and finishes, in case they can correlate this with some other activity.

When the interference appears do you see any other carrier changes in the whole transponder ?. Maybe someone is sometimes transmitting two carriers and when this happens their BUC sends out 4 carriers, the intended ones plus the 2A-B and 2B-A intermodulation products.

Observe the interferer carefully. If it is pulsing rapidly (TDMA) record this in zero span and tell the satellite operator.

If you can still see the interference when you point the dish well away from the satellite, like down horizontally around the horizon then the interference is from some terrestrial source such as a radio tower or radar.

Best regards, Eric.

Aug 7^th, 2008 at 10:44pm

The unwanted signal may come from a local interference.
If the interfering signal is still there when the antenna is off satellite, that may be the cause.