Satellite Internet forum http://www.satsig.net/cgi-bin/yabb/YaBB.pl Service Providers >> Satellite Connection in Africa >> Transmitting Through Antenna and Receiving through Another! http://www.satsig.net/cgi-bin/yabb/YaBB.pl?num=1414065553 Message started by Mohamed Elzaki on Oct 23rd, 2014 at 12:59pm

 Title: Transmitting Through Antenna and Receiving through Another! Post by Mohamed Elzaki on Oct 23rd, 2014 at 12:59pm Dears,This is my first post on this outstanding forum!  :)I'm a Transmission Engineer, and I'm relatively newbie to the VSAT.I have a simple question about a VSAT system scenario:On the Hub side, can I use a 9.3m antenna with BUC (for transmit) and using another 7.3m antenna with LNB (for Receive)?Knowing that the distance between the two antennas is about 15m only.And if it is possible, the LinkBudget should be calculated based on the smaller antenna, (i.e. the 7.3m) one?Thanks in advance ..Mohamed Elzaki "Conan"

Title: Re: Transmitting Through Antenna and Receiving through Another!
Post by Admin1 on Oct 23rd, 2014 at 5:44pm

Quote:
 On the Hub side, can I use a 9.3m antenna with BUC (for transmit) and using another 7.3m antenna with LNB (for Receive)?Knowing that the distance between the two antennas is about 15m only.

I can see no problem doing that. I would make sure that the earthing (grounding) of both antenna structures and the indoor hub equipment was all bonded together.

Quote:
 And if it is possible, the LinkBudget should be calculated based on the smaller antenna, (i.e. the 7.3m) one?

A VSAT system involves two independent link budget calculations, each involving an uplink joined into a downlink.

The first is the hub to remote direction. In this case the uplink earth station transmit dish is the 9.3m hub size.

The second is the remote to hub direction. In this case the downlink receive dish is your 7.3m hub size.

In both cases use the actual dish sizes involved.

Your satellite operator will be able to help you and they should have no problem simply inserting the correct diameter sizes and HPA powers in the relevant boxes on the two spreadsheets.

Try 'playing' with the link budgets yourself using Satellite Link Budget Calculator, or similar.

You will find that your hub dish sizes are both 'very large' and that the exact sizes make little difference overall.

In the direction hub to remote, your BUC power (watts) will be reduced by -2.1 dB (a factor of 0.616) if you use a 9.3m dish rather than 7.3m dish, while keeping the uplink EIRP unchanged.  There will be no effect on the overall C/N at the remote.

In the direction remote to hub, the downlink C/N will be higher but is likely to have little effect on the overall C/N which will be dominated by the uplink C/N at the satellite.

Best regards, Eric.