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AO-40 Reception



Good Morning to All,

I would like to add my two cents worth on receiving the AO40 S2 MB.  I
have Always received the beacon with a single 21 turn helix using both a
fully RF modified Drake (no crystal change) and a Trans System 3733 with
the stub cut.  Although I previously thought that the 3733 was better
than the Drake I have determined that the Drake I had up had some
instability in the front end (it had the noise I and others have
described).  I plan to put my other Drake up soon and compare the two
again.  I think they will be very close.

I believe the biggest problem in receiving the signal is knowing where to
tune.  Both my Drakes and both Trans System converters are within about
10 khz of correct when first turned on.  There is some drift but the
drift is not significant compared to the doppler.  I would not be able to
find the signal when it is weak if I did not use IT to tell me what the
doppler is. If you add that to any pointing error when using a narrow
beam dish you might miss the signal altogether.  The third factor is
squint.  All three of these factors have to be in my favor to hear the
beacon.  In it's current state the signal here is about 15 db above the
noise (forget S meter readings as they mean nothing) at AOS (from
perigee) with a squint of under 20 degrees and a range of 10k or less.  I
get good CRC TLM at that point.  I hear the signal until the squint gets
to be somewhere around 30 degrees and the range gets to about 20K.  I
believe the controlling factor is more squint than range.

With my current setup I was able to make a number of contacts when the
transponder was on and I only woke up LU-LU two times!  Having said that,
it is also obvious that while my setup is good enough for the beacon it
is barely (or not at all)  adequate for the transponder.  I have a DEM
preamp to put up when I am through playing with antennas and converters.

If you can't hear AO-40 you can forget UO-11 as a test source. It's
signal with my setup is 20 db down from the best signals from AO-40 and
the doppler and aiming problems are multiplied because it moves so fast.

I can also hear the beacon at 55K to 60K range with a low squint angle
but the signal is weak and I can't decode TLM.  Once you hear it once you
will know where to listen (if you know the doppler at that time) and you
can eliminate one of the three variables.

I echo Ed's comment.  Don't give up!

73's de Jess - W4MVB
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