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iDirect infinity : Max throughput with smallest dish ?

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Jun 15th, 2010 at 9:05pm  
iDirect infinity: What is the Maximum throughput with smallest dish possible???

Who out there is pushing 6meg down and 6 meg up with iDirect?  Or even something close to that?

We are looking to run 6 up and 6 down.  We need the smallest footprint possable...    Anyone got any suggestions?  
1.2M dish with 16w BUC????
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Reply #1 - Jun 16th, 2010 at 10:17am  
That's going do depend on the link budget, and the satellite that the service is on.
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Eric Johnston
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Reply #2 - Jun 16th, 2010 at 11:11am  
The downlink to your small dish is not a problem. There are many satellites with high power downlinks intended for antennas under 1m diameter. Remember that all satellite TV receivers are receiving mutiple carriers with bit rates in excess of 30 Mbit/s.

For your uplink, the problem is that you may cause interference into the adjacent satellites. To keep your uplink power down you need to try to find a satellite that has a reasonably small size uplink beam, so it has a high G/T receive at the satellite. Being near the centre of an uplink beam will help. Then do link budget calculations.  Having a really large receive teleport dish at the other end will help. Contact the satellite operator for more exact link budgets, and rules about your off-axis emission limits towards the adjacent satellites.  Use advanced turbo coding and lower the FEC rate so that you need minimum Eb/No overall.

If you use a high power BUC with a small dish make special arrangements to support the weight of the BUC. A heavy BUC may distort the dish and severely degrade the gain and increase adjacent satellite interference. The RF radiation hazard to people is also severe so make certain no one can get into the vicinity of the dish when it is transmitting. 16W will cook your eye lens in a moment.

Best regards, Eric.
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Reply #3 - Jun 16th, 2010 at 1:09pm  
Thanks Eric!

Our hub dish is a 3.8M with a 700Watt twt.
We are looking for the smallest foot print available.  Seems like we will have to go to a bigger dish on the remote end....   Kind of a bummer because these gigs are usualy for a day, and a 1.2 is quick and easy to set  up.   
I was reading in another thread someone recomending a 1.2M with a 45Watt BUC to push 6meg/6meg, what do you think?
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Eric Johnston
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Reply #4 - Jun 16th, 2010 at 3:27pm  
Do you have any experience with lower bit rates and a 1.2m dish ? If you can make 256k work with say 1 watt, then 6 MHz will need 24 watt. If you can make 256k work with say 2 watt, then 6 MHz will need 48 watt.

Note your test location in the uplink beam contours. If you are moving about to other places further from the beam centre, more eirp power will be need. -3 dB down on the uplink G/T contours means twice the watts or 1.4 times antenna diameter (=+3dB gain) is needed.

The sidelobe interference problem really comes with smaller dishes which have a wider main beam and less discrimination between the main beam gain and the sidelobe gain. If you are happy with 1.2m then stick with that and widen out the carrier proportional to the power. As long as you widen the carrier bandwidth proportional to the watts then the interference/40kHz into adjacent satellites will remain unchanged.

Best regards, Eric.
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TDMAMike
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Reply #5 - Jun 18th, 2010 at 12:00pm  
I dont think he means 6MHz. I am pretty sure he is talking about the IP data rate of the carrier. At QPSK .793 that IP data rate translates to approx 5.08 MHz.

A 1.2 with a 40W should close it (caveat: that statement is somewhat dependent on the operating location in the beam). A link budget is definitely warranted, just to be sure. That 3.8m on the hub side is pretty small...and as Eric eluded to, ASI could be a problem as well.  That is a lot of return carrier for a little 1.2...

On occasion, I close 4Mbs of upstream (QPSK .793 TPC) with a 1 meter and 25w Xicom. I don't do it often, because there isnt a lot of weather margin due to the BUC being so close to saturation.

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Regards, &&&&M
 
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