Sky dish size

[Bananahead]

If I move from a 78cm dish to a 88cm dish how much stronger will the signal be? With a 110cm dish give a much stronger signal?

( I tried searching but couldn't find a sensible answer)

 

[davemurgatroyd2]

Your location is essential on this sort of query and which satellites you wish to receive.

In general a larger dish will give a larger signal however it is very easy to overload the tuners in a satellite receiver with too large a signal - for example using a dish larger than 80/90cm in the south of the UK to receive Sky/freesat from 28 East

 

[Bananahead]

This is for Zurich. 78cm has been fine for HD until the new UK beam satellites came on stream recently. Now there is occasional signal breakup in bad weather.

 

[grahamlthompson]

Principle is the same as a reflecting telescope. Doubling the mirror area collects twice as much light from the same source. Doubling the dish area (assuming the lnb collects from the full dish area) you collect twice as much rf energy.

 

[grahamlthompson]

This is for Zurich. 78cm has been fine for HD until the new UK beam satellites came on stream recently. Now there is occasional signal breakup in bad weather.

Someone local should be able to tell you required local dish size to receive Astra 2E and 2F UK spot beams.

There are a number of websites that report on reception conditions for the above.

 

[Bananahead]

The problem with websites is that the reports are anecdotal - along the lines of "80cm gives me 90%" "I wouldn't use less than a 100cm" but what I would really like is a technical explanation to get away from suck it and see.

I found the following gain numbers for different sizes for Triax dishes

78 = 37.1 dbi
88 = 38.8
110 = 40.2

(now if I understood what dbi was )

 

[grahamlthompson]

The problem with websites is that the reports are anecdotal - along the lines of "80cm gives me 90%" "I wouldn't use less than a 100cm" but what I would really like is a technical explanation to get away from suck it and see.

I found the following gain numbers for different sizes for Triax dishes

78 = 37.1 dbi
88 = 38.8
110 = 40.2

(now if I understood what dbi was )

When comparing add-on antennas, what does dBi mean? How do I choose? Wireless Networking Forum FAQ | DSLReports, ISP Information

Decibel is a logarithmic measure. +3db is twice the power

Decibel - Wikipedia, the free encyclopedia

 

[Bananahead]

It looks like the 88 may be the way to go then.

Thanks for the help.

 

[MartinPickering]

On the basis that the LNB "sees" a circle which is the diameter of the dish,
A 78cm circle has an area of 3.14 x 39 x 39 = 4776 sq cm
An 88cm circle has an area of 3.14 x 44 x 44 = 6079 sq cm.

Taking the percentage difference as (6079 - 4776)/4776 x 100 = 27%
That approximates to the percentage signal increase you might expect.