Re: [amsat-bb] AO-51 Mode J Desense Solution

["hasan schiers" <schiers@xxxxxxxxxx>]

Hi John,

To test how well the diplexer as-high-pass-filter concept worked, I ran a
series of tests at varying power levels. Without the diplexer, even turning
the power on the 847 all the way down (no wattmeter indication at all),
still produced dramatic overload of the preamp when transmitting on 2m and
listening on 70cm.

I then put the diplexer as high-pass in front of the preamp. I was able to
set the power to maximum at 160 watts output (not uplinking to the
satellites, of course), and there was no desense or other untoward behavior
in the face of this large amount of power. It should be noted that the 2m
feedpoint is within 6 inches of the 70cm feedpoint.

So in my case, lowering the power accomplished nothing, while using the
diplexer as high-pass, allowed the 70cm preamp to function perfectly in the
face of 160w of 2m rf only 6 inches away.

Having operated Mode J for many, many years, it was always very frustrating
to try to cope with the preamp overload problem. I have tried home made low
power high pass filters (that worked, but could not be left in-line during
xmit), a tunable microwave modules 70cm filter rated at 10w max, and an ARR
Cavity filter. The cavity was large and heavy, and subject to temperature
variations.

The advent of this use for a common diplexer is a great solution to a
nagging problem for mode J. I much appreciate Drew putting me on to such a
simple and readily available solution. It works, it handles plenty of power,
and is inexpensive.

73,

...hasan, N0AN
----- Original Message ----- 
From: "John Mock" <kd6pag@qsl.net>
To: <amsat-bb@AMSAT.Org>
Sent: Sunday, August 01, 2004 5:07 PM
Subject: [amsat-bb] AO-51 Mode J Desense Solution


> I have another solution to the de-sense problem.  I can tell you that the
> times that i experienced the most de-sense on AO-27 was when i tried to
> work the opposite coast on 5W (instead of 1W or 140mW).  Tuning up my
> antenna helped, but the better solution is to use less power.  That's one
> reason i typically ran 140mW on Pacific passes and 1W on transcontinental
> passes; it's simply that i could hear myself better.  Alas, that didn't
> work as well on UO-14, as it was so popular.  Thus i tended to strongly
> prefer AO-27, even though it was harder to hear.
>
>        -- KD6PAG  (Networking Old-Timer, Satellite QRPer)
>
>
> [Note: I never send unsolicited binary attachments and if you receive
anything
> purportedly from <kd6pag@qsl.net> that isn't signed with my callsign, then
it
> probably isn't from me.]
> ----
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