Re: Dish


johnrigsec@...
 

In a message dated 07-11-03 04:54:59 GMT Standard Time, a.van.belle@...
writes:

Modern LNB's are only suited for offset dishes. The feedhorn is
different to get a smaller beamwidth, compared to most prime focus
dishes with F/D=0.5 (offsets have F/D of 0.6 to 0.7).

You can put a modern LNB in the focus of a prime focus dish, but you
will only use 40 to 60% of its surface, giving low signal level.
Arne,

Thanks for your useful information.
I knew there was a difference between (early) prime focus RF equipment and
present
day offset equipment but not sure quite what.
I suspect I'm not the only person to learn something new.

My early prime focus LNC's (as they were called in those days) have wider
apertures
and scalar feeds.

But you will be shocked by the noise figure of these oldies, 1.3 to
1.8 was excellent these days !
Nowadays you have 0.6 to 0.7 dB for 1/5 of the price !
Indeed, my first 10/11 GHz LNC from Avantek had a noise figure of 1.8 dB and
cost,
in 1986, £1,200!

Sorry, a bit off topic for MSG, but it was through C-band and Ku-band
satellite TV
that I got into weather satellites.
And the rest, as they say, is history.

One thing, for us in the UK who are only supposed to install ONE dish per
property,
take a look at the ultimate(?) multi satellite dish system at <A HREF="www.wavefrontier.com">
www.wavefrontier.com</A>
you can have your (multiple) satellite, satellite TV and EUMETCast, from one
dish!

Regards,
John.
RIG


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