--- In MSGfirstname.lastname@example.org, johnrigsec@a... wrote:
Question.with an (elliptical) offset dish?
Or, can you also place it at the focal point of a prime focus dish?John, Offset dishes may look elliptical but seen from the sat (or
from the LNB) they are ROUND !
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.
With Eumetcast on the low band (11096 Mhz) you may be able to find a
used "old type single band" LNB with a scalar feed ring assembly and
H/V servo mechanism or Ferrit H/V switcher.
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 !
Another drawback of Prime focus is that they do gather snow !
At 1.7 Ghz this is no problem but 2 cm's of snow in the dish can make
your a 11096 MHz signal disappear completely.
Arne van Belle