Satgen309  Microwave Reception       by GM4IHJ                25 Feb 95
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Most signal reception from satellites now occurs at microwave frequencies.
This is generally assumed to require conspicuous dish antennas. But, while
it is conceded that a dish antenna may be highly desirable, it is often
the case that it is not a practical proposition , because of, local laws,
the XYLs firm exclusion of anything ugly or mechanical, or , high winds
and adverse weather conditions.

So what can a flat dweller, or igloo owner do ? First it must be said that
the dish need not be out of doors. It can be inside a building provided
that it can view the sky through single thickness glass ( further obscured
if necessary by a thin curtain ). Double glazing can produce substantial
attenuation and refraction, but a dish located half a metre behind a
single glass pane and gauze curtain can receive 3 GHz to 12 GHz signals
with only minimal attenuation, even when the signal is coming in at a
relatively low incident angle to the glass of say 30 degrees. You can do a
simple test for attenuation by checking your antenna and receiver using
Sun noise as your target, window open versus window closed if in doubt.

However , She who must be obeyed, may simply not allow a dish indoors. In
which case you can try putting a diffraction grating ( marking ink circles
on thin plastic) on the inside of the glass, with the LNB located at the
focus further back from the window and suitably disguised as a pot plant
or other room decoration. Equally possible you can put the diffraction
grating outside on a suitable garden wall and site the disguised LNB in
front of it.

A quite different alternative particularly when the satellite you want to
receive is at high elevation is to receive the signal through a roof sky
light. GM4IHJ has two big windows in the roof, one facing south , the
other facing north, providing good viewing ( and a warm sheltered indoor
position out of the Scottish winter), with reception of Oscar 13 , and CIS
Molniyas, via a collection of helical antennas for the various microwave
frequencies. Originally single helixes were used, but these were unwieldy
and have been replaced by neater, shorter, double and quad helix
combinations.

Different yet again and not yet seen on the Amateur radio scene, is an
outdoor type of antenna which uses a flat metal plate which has milled
dipole slots in it suitably coupled to form a broadside array. BSB an now
defunct UK satellite TV broadcaster produced a few antennas of this type
for 12 GHz. Those that passed the specification worked well, and can be
very inconspicuous. But unfortunately these antennas require extremely
precise antenna pattern tolerances, which are not easy to mass produce.
However a radio amateur with plenty of time and a good machine shop should
be able to produce something useful in this line if none of the other
solutions advocated here will suffice.
73 de GM4IHJ @ GB7SAN or gm4ihj@delphi.com