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80 posts

Master Geek
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Topic # 87940 10-Aug-2011 23:31
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I've seen a local provider selling feedhorns for getting Intelsat 5 C-band on a 90cm dish, i.e a bit smaller than normally what you need. I get Intelsat 5 C-band on a 1.2m dish for instance. Is that idea scalable? For instance I am looking at a 2.4m dish, but the EIRPs for Asiasat3S and 5 would suggest I need a 2.7 or 2.9m dish. With a feedhorn and/or maybe an amplifier on the signal anyone like to guess if I could get watchable signals with the 2.4 metre dish? I have line of sight to the sats as I live on a hill.

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6605 posts

Uber Geek
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  Reply # 504956 11-Aug-2011 12:55
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Argh, big post lost.

Guts of it were:

You don't get masthead amplifiers etc with satellite, like you do with Terrestrial transmissions.

Get a good quality LNB.

http://jayx.co.nz/CLNB's.html



80 posts

Master Geek
+1 received by user: 2


  Reply # 504966 11-Aug-2011 13:24
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Yes Jaxson,
Ok thanks on the amplifier news.
I'd seen your feedhorns on that URL and will adding a feedhorn give me a bit better signal if I was using a 2.4m dish?

 
 
 
 


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546 posts

Ultimate Geek
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  Reply # 505149 11-Aug-2011 19:02

Hi,

The scalar rings are used on C-band LNB's to optimise them for "offset" dishes. They basically focus the signal reflected off the dish better.

Using a scalar ring on a centre fed (prime focus) dish will not result in performance improvement as they are designed for an offset dish.

If you can buy a large offset dish you can get a signal advantage over the same size centre fed dish because the LNB itself is not in the way of the signal hitting the dish and the LNB will likely face above the horizon instead of at the ground. (on a centre fed dish the lnb faces the ground which is a large source of noise= less signal/noise ratio).

The other reason a 90cm offset works as well as a 1.2 centre fed dish is that single piece offset reflectors are generally more accurately shaped than multi segment dishes.

Hope this made sense...




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  Reply # 505218 11-Aug-2011 21:14
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Yeah as above. If it's a prime focus dish then adding anything to increase the area around the lnb actually blocks signal from falling on the dish. Who know though, if it does work it may be compensating for a problem somewhere else.

Using a good sensitive LNB and optimising your setup is really the best way to be going. Someone here might have first hand experience with your size dish and the satellites you are after.

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