[amsat-bb] Re: Polarity Switcher Relay - repost
bob at evoria.net
Wed Sep 5 11:36:54 PDT 2007
--- Bruce Robertson <broberts at mta.ca> wrote:
> An important factor you don't mention is the coax to your antennas. If you
> are not using preamps, the losses of the cables decrease the noise figure
> of your reception by the same ratio, and this can add up very quickly to an
> unworkable situation.
Sorry, about that. I'm using wireman's #106 which is a low-loss foam
RG-8 type with both braid and foil shielding. Also, there's only about
35 feet of it, so the loss should be be very low.
> I think most of us also believe from experience that mast-mounted, low
> noise preamps (from ARR or SSB USA) do far more for a station than polarity
> switching. These are not inexpensive additions, but, especially on 70cm,
> they are indispensable.
Here's what's happening. From about 20 degrees up to about 30 or so,
reception is iffy. After that, I sometimes have full quieting and sometimes
nothing. I suppose I need to do a real study of it on one satellite, but
it just seems that it should be a polarization issue. I do have a spare
coax going up there, so I guess I could just make a LHCP version to
be sure. Getting it out on the roof means that I have to make a much
more robust version. I was hoping to put that off until I was completely
sure that I've got a configuration that works properly. It's much easier
for me to just move the antennas to the back yard when mowing season
is over (I'm disabled). Fortunately, I have a semi-finished attic with easy
Another thing I've been thinking of is that once I'm comfortable with
messing around with relays etc on 70cm I might be able to use a DEM
preamp with my own switcher. Thus my question on the relay.
Bob - AE6RV
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