How to compare offset dish with Primefocus dish

Moradabad

Moradabad

SAT SPECIALIST INDIA
My Satellite Setup
One 12 Feet Heavy Antenna, one 10 Feet Double Rib Antenna

Dreambox Dm500S, DM 7025. HD Receiver,Envision,
Eurostar receiver, 4 Dual LNBS, 5 PFA Lnbs
My Location
india
Hi Friends,

Can anyone tell how can we compare a 8 feet Offset dish with 10 feet Primefocus dish,

Will 8 feet offset dish & 10 feet Fiber dish give same signal ?

Thanks:-worship
 
Direct comparison is not possible - since both dishes may be different quality and gain. For very rough approximation, you can equal 100cm offset to 120cm primefocus dish.
 
That's a very big question...

....depends on so many things.. the quality of both dishes have to be like for like yes...

....but are they solid or mesh,

....is it for C or KU band..

and

...does the location suffer high local interference and is the aim likely to suffer excessive ground noise or not.
 
Also should be noted, the bigger primefocus dish is - the less area of it is shadowed by LNB, so less difference will be in signal strength. Also, most broadcast/uplink dishes are primefocus, I think there's some good reason in it :)
 
see.... antenna noise temperature x elevation ...10/20/30 degrees...

_http://www.ascsignal.com/images/content/vsat_products/pdfs/Type%20243%20Kuband.pdf

or

_http://www.gdsatcom.com/Antennas/Data_Sheets/1250Back.pdf


Offset dishes have a drawback that they can suffer more from ground noise and local interference (depending on elevation of the sat x the location rural/ city) compared to prime focus dishes of the same area.

The design of the offset means the dish face & the LNB are more exposed to both where as the prime focus dish points up more for the same elevation thus less exposed to ground noise across the earth in front of it and the back of the dish defends the lnb & dish face more from direct ground noise & locally produced interference ... from underneath the dish.

The LNB is also more sheltered than the offset dish, being lower in the deeper parabola of the prime focus than the Offset's more exposed LNB.

If it's a city location with high local interference &/or located low down giving higher ground noise locally and in it's view path.. the prime focus could beat the offset... purely on noise defending.

Obviously, it only applies to solid dishes though... .....wire mesh dishes will allow 'some' noise through the wire mesh depending on the frequency.
 
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