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RE: AO-40 reception question



Floyd,
Feed polarization DOES make a difference. Linear to circular + 3db. I am now
using a James Miller Patch LHCP (must be reverse feed when using a dish)
feed, from England, on my 1.2 meter offset dish. Works very well. If to take
a look: http://www.jrmiller.demon.co.uk/products/patch.html
I went from 60cm to 1.2m and lin pol. to RHCP and gained about 9db better
S/N ratio. WHAT A DIFFERENCE.
Good luck.
Gunther Meisse
W8GSM
AMSAT LM: 594


-----Original Message-----
From: Floyd Sense [mailto:sentek@sprintmail.com]
Sent: Friday, September 14, 2001 11:35 PM
To: gjmouse@neo.rr.com; amsat-bb@AMSAT.Org
Subject: Re: [amsat-bb] AO-40 reception question


I read somewhere recently where circular polarization should be almost not a
factor with AO-40 - obviously, that wasn't totally correct.  I plan to use
one of the barbecue dish antennas for 1.2 initially, but wonder if I should
consider using something with circular polarization (and switchable)
instead?  What type of antenna are you using for RHCP on 1.2?

K8AC
Floyd Sense - Angier, NC
----- Original Message -----
From: "Gunther Meisse" <gjmouse@neo.rr.com>
To: <amsat-bb@AMSAT.Org>
Sent: Friday, September 14, 2001 12:13 PM
Subject: RE: [amsat-bb] 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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