SatSig topic:

Terasat BUC hiccups

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Sep 3^rd, 2008 at 4:43pm

Dear all

i ve a problem with my newly installed Vsat network, basically at the hub. The hub is meant to use a 25watt terrasat Buc, but we are testing it with a 10watt BUC using only 2 remotes. i can log in to the 10watt BUC and ping as well ( using the M & C interface) but i can't do that with the 25w buc. conclusively i can't receive lock on the remotes with this 25watt. kindly assist on what to do, do i need to change the power level from the external power unit supplying the BUC or my satellite provider has to adjust some parameters for BUC to transmitt on thesame frequency

Regads, Delson

Sep 3^rd, 2008 at 5:34pm

Read the manuals for the two BUCs

The 10W BUC may work with 24V or 48V DC supply.
The 25W BUC may need 48V supply.
Check with Terrasat.

You need to be able to communicate with the 25W BUC before you use it to set parameters gain or ALC level etc. There is probably a MUTE/UNMUTE control also.

You need to set hub modem TX to a reasonable output level and also set the BUC gain to a reasonable level. Avoid extremes. Adjust the level cautiously so as to not overdrive the BUC. Each 1 dB step increases the power by a factor of 1.26. If you are at 20W and go up 1 dB the power will be 25.2W. A 3 dB increase could be a disaster, like attempting 40W; a bit like blowing up an audio amplifer loudspeaker. The power reading is only accurate to +/- 1 dB.

Start with a low level output from the modem and a high attenuation in the BUC with a CW carrier till the satellite operator verifies that you are pointed to the correct satellite, polarisation and frequency.

For single outlink carrier from the hub, the BUC power at the hub is related to the hub dish size, the outlink bit rate and the size of the smallest diameter remote site or the most disadvantaged remote site in terms of weak beam edge location.

Only if you are transmitting multiple carriers to many remotes will the BUC power be related to the number of remotes. The 25W C-Band IBUC has a rated multicarrier operating point at -6 dB output back off (-9 dB per each of two carriers), so if you want to transmit multiple carriers your maximum composite output power is 6.2W or 3.1W for each of two carriers.

If you want to test with a 10W BUC at the hub, consider reducing the outlink bit rate by half.

https://www.terrasatinc.com/documents/C-bandIBUCDataSheet081508.pdf

Best regards, Eric.

Sep 3^rd, 2008 at 6:51pm

Thank you Eric, i 'll start with the parameter variation as you said and also scrutinize the manual.

Regards, Delson