RE: [amsat-bb] Re: Best pre-amp for Mode S

["Howard Long" <howard@xxxxxxxxxxxxxx>]

Helo Karl

> I have been playing with AO40v2.0.xls and it appears that the first 8-10db
> gain from a pre-amp does help but going higher than 16db does not seem to
> make a great impact.

This is true if you have relatively little feeder loss between your preamp
and downconverter/receiver. I think you stated in the previous post that you
have a feeder run of 50', which with 9913 would present perhaps 6dB loss, so
your statement sounds about right.

I also use a preamp at the masthead and for my sins I have 180' between
shack and masthead which gives me over 20dB of feeder loss at 2.4GHz.
Therefore I use a dual stage 37dB gain unit.

Of course, alternatively you can always downconvert at the mast instead and
use your cheap RG-58 to feed.

The reason I use a preamp at the masthead rather than downconvert there is
that it enables me to use the antenna in the terrestrial section of the band
as I'm lucky enough to have a local beacon for system (and operator) sanity
checks. Most downconverters with 144MHz IF's won't cover both the satellite
and terrestrial subbands (although a modified AIDC 3733 I have does a pretty
good job covering both).

73 Howard G6LVB


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