MY X3 EVALUATION NET LED is becoming off every minute without affecting the internet traffic, but my TX power is too high up to  -15.5 dBm so how can i reduce up to -20 dBm. If any one helping me about this issues I will be very happy.

Thank you
Fahad

Ask your hub to commission your site.

They will test your transmit level in CW mode at many modem output levels starting at say -35 dBm and going up in 1 dB steps and will plot the graph of modem output level versus measured satellite carrier level.  When the BUC gets near to saturation they will observe and record the -1 dB gain compression point and set that as the maximum your modem will ever be told to transmit (for example, during a serious rain fade). During clear sky your BUC should be operating at or below one quarter of its rated power. i.e. backed off by 6 dB down; this means that you can experience a 6 dB rain fade and, using uplink power control, fully compensate, with no change in level of your uplink into the satellite.

Best regards, Eric.

There are a few things that may affect your power levels. It may help to peak the alignment. If your coax cables are poor quality, have issues with loose or corroded end connectors, or are too long you may allow extra losses into the TX chain. If the problem is not resolved, consider getting a stronger BUC or larger antenna.