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Re: Orbit 250 apogee



At 09:21 PM 5/18/01 +0200, you wrote:
>At 03:04 18-05-2001, you wrote:
>
>--snip--
>>Amateurs have published designs for 0.4 dB NF (28 K) amplifiers in QEX and
>>Microwave Update and antennas can easily be made with sidelobes that are 15
>>db down so that they only pick up 9 K of ground noise.
>
>Does this mean that using an offset-dish instead of a primefocus dish is 
>actually an advantage, since the feed is usually NOT pointed at the 
>ground, but upwards, so that over-illumination will not "see" the ground?

Hi Jens,
Yes, that is exactly what it means. You can get by with a smaller
off-set fed dish than for a round dish for the same S/N ratio.
As I recall, an 18" offset dish is roughly equivalent to a 24"
round one (receive S/N ratio wise). QEX has had some useful
articles. You can get the CDs of back issues from ARRL.
Tony AA2TX


>How big is the ground-noise contribution exactly?
>
>Is there anywhere I can read more about it?
>
>73 de OZ1LRG
>
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