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RE: AO-40 reception question



Bill,
The only observation I have is that in my experience, if a signal is truly
down in the noise, adding a preamp will do little good, often making
everything worse. The preamp amplifies the signal/noise package. Result:
Higher S meter reading, with the signals still down in the noise. The only
real fix is more antenna gain and proper circularization of the feed. I went
from 60cm/Lin polarization to 1.2m RHCP and totally fixed my problem. It is
now a great ear!
Good luck.
Gunther Meisse
W8GSM
AMSAT LM: 594


-----Original Message-----
From: owner-AMSAT-BB@AMSAT.Org [mailto:owner-AMSAT-BB@AMSAT.Org]On
Behalf Of Bill Howell
Sent: Friday, September 14, 2001 4:05 AM
To: Amsat List
Subject: [amsat-bb] AO-40 reception question


When AO-40 was first turned on for amateur use, I was able to hear
others' downlinks
well enough for an SSB QSO (sigs were in the noise, but useable).

Lately, it seems, (using the same equipment: Meyers dish, unmodified
3733, ft-847),
all the downlinks seemed to be down deeper in the noise and not
strong enough for a QSO.

I have swapped the 3733 with another one, with similar results. I
also tried using a different
wall-wart / bias-tee. No difference.

I recently added a DEMI preamp (recently tweaked by DEMI), between
the Meyers feed and the 3733.
The signals are helped by the preamp, although they are still pretty noisy.

I get S-5 background noise (away from the beacon freq), on the '847,
and the beacon itself is at S-6.

I know that on some passes, I was looking through a tree, but one
particular pass
was clear of the tree and still weak (could be a combo of good view /
bad squint).

I have a couple more things to try. I have the K5GNA filter to
install, and I need to try cutting the stub.

A friend of mine is also using an unmodified 3733 and finds downlinks
only strong enough
  for CW QSO's.


Perhaps all this is just tree / squint related, but in general, It
just seems like conditions
used to be better.






--

Bill Howell
University of Texas at Austin
College of Fine Arts
Office of Computing Technologies
N5ALO  Amsat 32459  QRP-L 415
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