How much sky does dish need to see?

Bill Wright wrote:


"Woody" wrote in message
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wrote in message
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If there are any incursion problems you can use a bigger dish which has a
narrower beamwidth.

That could help if the incursion was the source of radiated interference,
but not if it was merely a screen from the 'bird'.


What about the noise temperature (~290K) of objects within the dish beam
pattern but not actually casting a shadow on the dish? Presumably with
a typical Sky setup this is a second-order effect?

J

"John Sager" wrote in message
...
Bill Wright wrote:


"Woody" wrote in message
...
wrote in message
...

If there are any incursion problems you can use a bigger dish which has
a
narrower beamwidth.

That could help if the incursion was the source of radiated interference,
but not if it was merely a screen from the 'bird'.


What about the noise temperature (~290K) of objects within the dish beam
pattern but not actually casting a shadow on the dish? Presumably with
a typical Sky setup this is a second-order effect?

Yes, good point. I suppose that's what I meant by 'radiated interference'
really, without properly thinking of the correct way to express myself.

I have never knowingly experienced this effect, but I'm sure it must be a
factor. It would be interesting to set a crude experiment up with a dish
looking just next to a large object, then with the dish a bit further away.
Certainly minidishes should be susceptible because of their wide beam. It
should also be possible to calculate the possible effects by comparing the
noise level of the sky and, say, a brick wall.

Bill