SatSig topic:

TX power problem

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Oct 13^th, 2011 at 12:36pm

we have Vsat C-BAND and the satmodem is Idirect x3 evaluation the rx power is good but the tx power is very high -15.0000 dBm so the skylogic is saying you have to make your tx power lower up to -20 dBm how can I improve my tx chain upto -20 dBm please help

Thanks
-Fahad

Oct 13^th, 2011 at 1:18pm

mt tx power is

> tx power
Tx Power = -14.00 dbm
Max power = -14.00 dbm
Min power = -40.00 dbm
Power Gain = 3.00 dbm
Reference =    36
Inroute-Id Nominal-CN    Tx-Pow
er Correction Scaling
      36    9.00 -14.00    0.00 1

Oct 13^th, 2011 at 1:49pm

Alter the max power down to -20 dBm.

Even this may be too high. Plot the output power (measured at the BUC output locally or remotely at a downlink monitor site or the satellite NOC) versus the modem output level and then set the max power so that you can never exceed the -1 dB gain compression point of the BUC. This is a test that should be done at commissioning and the max power set then.

The max power might be reached during heavy rain when the maximum of uplink power control is applied. During clear sky conditions the level should be perhaps 6 dB lower.

Best regards, Eric

Oct 13^th, 2011 at 2:20pm

Dear eric,
thank for your quick answer,
now how can I improve the TX power to lower? I noticed when I turned on my satmodem was 18 dBi after few seconds it became -15.50 dBi

Thanks
-Fahad

Oct 13^th, 2011 at 6:56pm

If you are at a remote site, ask the hub to set a new maximum of -20 dBm for your modem max transmit power in the hub database.

It is possible that your levels, including the initial level are far too high. Get the hub to test at all CW levels from say -35 dBm up to -20 dBm and to measure the levels at the hub. Plot the graph and look where it starts to go non linear (-1 dB gain compression point). Set that as max. If you are already far above BUC saturation your signal will be severely distorted with high error rate and interference to other people etc and the hub software will think it is low level and tell you to send yet more power = disaster ! Initial commissioning must include the setting of the max power in the hub database to correspond with your BUC -1 dB gain compression point. The hub will then never tell your modem to go above this level, even during heavy rain. During clear sky the level should be well below the maximum.

Best regards, Eric