Sir ,
By Knowing the VSAT Dish size  and BUC capacity and modem , can we say how much uplink and downlink bandwidth we ca get MAX .. suppose 1.2 m, 1.8 m , 2.4m , 2.8 m and  BUC is 2W,3W, 4W, 10 W,20W .. modem linkstar , idirect etc .
Can we caliculate the MAX Bandwidth we can receive on the dish.

sir , is there any realation between the VSAT dish size and bandwidth , for suppose if the dish size is 1.2 mtr and we are using a 2 Watt  BUC and the modem is linkstar ,, can we predit what is maximum Bandwidth for the internet  ..  which we can get .. like 512 kbps downlink and 256kbps uplink like .. is it really dependes upon dish size and BUC capacity

Use your search engine to locate a link budget calculator. When fed the proper data - to include dish size and BUC output - it will provide the info you seek.

//greg//

Download to the VSAT
Satellites transmit carriers with 27.5 Msps mostly for TV purposes but some of these carriers are used for satellite internet access for the download path to the customers.  In such cases the download bit rate to the customers is about 30 Mbit/s.  A typical satellite TV or VSAT dish might be receiving many such 30 Mbit/s carriers.

Since such services operate on a shared basis, satellite service providers share out the traffic to each customer.  Someone paying $14,000 per month might get 2 Mbit/s continuous dedicated service, for GSM site for example.  Someone paying $70 per month might get "up to 1 Mbits" but shared with 100 other sites.
Your downlink bit rate is largely limited by how much you will pay.

Uplink from the VSAT to the satellite
Try the link budget (see previous post) and you will find your uplink bit rate is limited by your dish size plus your BUC power plus the far end teleport hub size.

Best regards, Eric.