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A dish and downconverter question

Good morning all,  a question or two about a dish and downconveter.

What I have:  a 1.2 meter offset dish and a 3733 downconverter.
The problem (like many)  poor to nonexistant recepiton of AO-40
I have the dish mounted horizontally (long side to the horizon) on an Az-El
mount.  Transystem 3733 downconverter with either a patch antenna or a helix.
To compinsate for the extremes in temp we are experiencing here I have 
a series string of power resistors attached to all long sides of the
downconverter and wrapped in pipe insulation.  Before I did this the
downconverter drift was so bad I could not use it. I can now control the
drift quite well by varying the voltage to the resistor string.
Drift now can be limited to a few kHZ.

We had a few days of warm weather and I had the system working well with
copy of the beacon and several contacts through the bird.  The pass
happened to
be one where the visual angle was low to the horizon.  I don't know if this
any bearing on the problem.  Some of the later passes were at high elevations.

now that we are back to cold weather I can't copy the beacon or anything else.
I did not have the resistor stack on during the warm weather.  
I have tried to monitor several passes allowing for squint and MA during
different times of the day with no copy at all.

I have tried to eliminate as many problems as I can think of but now need
some suggestions.

Comments anyone?

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