[Moon-Net] Fwd: Prime-focus vs. Offset-dish

Barry Malowanchuk ve4ma at shaw.ca
Thu Nov 24 00:30:15 CET 2016


Hi Rex,

You don't really want to go much lower anyway since the ground noise /atmospheric noise starts to hurt badly on the high bands.  But if you have no choice....station at other end is 12000 miles away...you have a problem.  The only regret I have is that I cannot put the dish on the horizon so that I can focus the feed on a point source.....sun and moon are too big at 24 GHz and up with a 2.4 m dish !  I also have a chain link fence that gets in the way at low angles.

Best 73
Barry VE4MA


----- Original Message -----
From: "Rex Moncur" <rmoncur at bigpond.net.au>
To: "serge" <ve1kg at eastlink.ca>, dl7yc at snafu.de, moon-net at mailman.pe1itr.com
Sent: Wednesday, November 23, 2016 1:56:21 PM
Subject: Re: [Moon-Net] Prime-focus vs. Offset-dish

Hi Serge

One issue with offset dishes that has not been discussed so far is how to
mount them in a way that allows you to beam low at the horizon.  I notice
that often people with offset dishes cannot work down to zero degrees as the
bottom of the dish comes back against the vertical part of the mount.  This
can be resolved by putting the feed at the top but then the feed is more
difficult to access.

Another solution is to have the vertical mounting extended into an L shape
to mount the centre of the offset dish so it is clear of the vertical part
of the mount when beaming at low elevations.  The downside of this it that
all the weight is leveraged to one side of the mount and you need a much
stronger mount to maintain accurate elevation.



73 Rex VK7MO



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