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Nov 23rd, 2011 at 4:07pm
You need to talk to your hub.
If the modem output transmit level is too low, say -20 dBm, then your transmit bursts will not be received at the hub and the hub will tell your modem to increase its output.
Once the level is high enough for nominal good reception at the hub (say C/N=10) the hub will stop telling your modem to increase its output. This final level setting should be several dB below your maximum setting. This means that the hub can tell you to make further temporary increases during heavy rain.
Your maximum setting is determined at commissioning and will correspond to the maximum power rating of your BUC (P-1dB). The hub tests your site by gradually increasing the CW level from -20 dB in 1 dB steps while measuring the actual output signal and determining when your BUC amplifier goes non-linear as it approaches saturation. This -1 dB gain compression point defines the maximum setting.
If you allow the modem output to go higher the transmitted modulated signal transmitted may be of high power but is so distorted that hub can't receive it properly and thinks the high errors mean low level so increases you further, making matter worse. Is important to do the - 1 dB test properly as overdrive of a BUC may damage it and will cause interference to other users of the satellite.
If your site never gets to transmit an adequate signal into the hub then you may have a mispointed antenna, too small an antenna or BUC, distorted antenna or low DC volts into the BUC due to cable corrosion. The transmit beam is narrower then the receive beam so alignment to the exact centre of the receive beam is critical even if you see no change in the receive signal when fine pointing the dish. If all your kit is good you can improve the signal into the hub by 3 dB if you halve your transmit bit rate.
Best regards, Eric.
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