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two satellite links on one antenna with two ports

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Ex Member
Ex Member

Jan 15th, 2017 at 8:17am  
Hi all

I have single 7.3m antenna with one buc, lnb and modem.

i am planning to use the two polarization of the same satellite to increase my internet bandwidth.

will the BUC rating affect the bandwidth of each link ?
do i need 4 port or it is still feasible on two port i have ?
does the two carriers need to use different/opposite transponder of the same satellite ?

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Posts: 1131
Reply #1 - Jan 15th, 2017 at 4:30pm  
If you have an operating system measure how much power you are transmitting. Is this much less than your BUC rated power ?   Ask the NOC if you can increase the power and stay within your existing transponder lease (PFD and bandwidth).  If you are allowed to increase power, consider changing to a higher order modulation/FEC to get more information bit rate through your existing lease bandwidth at no extra cost. Alternatively, purchase more bandwidth on the existing polarisation. You will need a larger BUC, generally in proportion to the information bit rate increase and you may have to change frequency to fit into an available spare range of transponder bandwidth. Check what you are offered is clean and clear of existing interference.

The BUC power rating required depends on the power needed in the link budget, plus uplink power control margin, plus extra backoff if you are operating multicarrier.

I do not recommend multicarrier operation. If you really have to operate two carriers, of equal power, both on the same polarisation, then the BUC power rating needs to be at least 4 times the individual carrier powers. This is expensive. You must also have a waveguide coupler at the BUC output and a
microwave spectrum analyser to monitor and plot your transmit spectrum, otherwise you cause intermodulation interference.

To operate additionally on the other polarisation you will need a 4 port feed. I don't know if you will be able to use your existing 2 port OMT and waveguides. It depends on the design and if each waveguide can carry both the transmit and receive frequencies.  If yes, then you need two diplexers to add to the existing guides.  In no, as would certainly be the case with C band, where the 4 and 6 GHz guides are quite different, you will need a complete new 4 port feed system. Ask the antenna manufacturer and get prices.

You will then have two transmit waveguides, one for each polarisation and two BUCs, also two receive waveguides and two LNBs.  Consider adding redundancy switching with 3:2 redundancy for the BUCs and LNBs.

Bringing into use the other polarisation will mean your customers will be of two types with their VSATs set up on different polarisations.

If you operate on both polarisations there is no need for the leased bandwidths to be co-frequency. Ask what bandwidths are available.
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