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Re: 2401 MHz beacon advice



I would be curious about your results with the DEM kit. I built one and,
while it works, I didn't expect to see as many signals from it as I did....
The instuctions for cutting the stripline filter were confusing at best and
the power output never did reach stated value. Of course the output was
PLENTY for what I wanted, a weak signal source. Let me know how you make
out.

----- Original Message -----
From: Art Goldman <aegoldm@lts.ncsc.mil>
To: Robert Jewell <ac9r@home.com>
Cc: <amsat-bb@AMSAT.Org>
Sent: Wednesday, May 02, 2001 6:09 PM
Subject: Re: [amsat-bb] 2401 MHz beacon advice


> Bob:
>
> I seem to recall that Sam from Philips-Tech told me the
> focal point was 14". That's just about where my dipole is.
> The reflector is attached. Perhaps the reflector should be
> at 14"? Or not there at all? We are expecting a signal
> source from DEM this week. Then we will run some tests to
> see where it plays the best.
>
> I've had no trouble with ao40rcv but my laptop is a 433 Mhz
> celeron, and it seems to keep up just fine. Occasionally, it
> seems to lose its place and stick halfway through a block
> decode, but then it picks up again. It's hard to tell if
> this is a computer or receive problem.
>
> Art
>
> Robert Jewell wrote:
> >
> > Art:
> >
> > Have you calculated the focal point of the Phillips SPG 36 antenna?  My
> > Phillips calculates to a focal point of about 14".  The antenna that
came
> > with the dish appears to be a log periodic and the first element appears
to
> > be near 14" from the dish.
> >
> > My 38" X 26" parabolic grid antenna that came with my 3733 has a
calculated
> > focal point of about 16".  "Others" and myself are using a dimension of
> > 12.25" to the dipole??????????????  I will move the dipole back to about
16"
> > and see what happens.  Am I making the calculations correctly?  F= d
squared
> > / 16h.  F= focal point, d= diameter (longest dimension) h= distance from
the
> > back of the dish to line from side to side of dish.  OR, am I only
measuring
> > a "piece" of the dish?
> >
> > I also have a "fiberglass" DSS Scientific Atlanta dish here, 39" X 36"
with
> > an offset feed.  I have calculated the focal point at 28" if it is on
> > center.  Setting the 3733 dipole at approximately the offset focal point
of
> > the former feed (26"), gives good results with the dipole facing the
dish
> > and the downconverter facing away from the dish.
> >
> > I am "testing" five systems here just because I am a Ham:
> >
> > 1.  10 FT C Band with 3733 dipole taped to feedhorn. The downconverter
comes
> > off at 90 degrees to existing feedhorn and is taped to one of the four
> > feedhorn support legs, with the dipole vertical.  "Armstrong" azimuth
> > rotation, and existing positioner for elevation rotation with a WineGard
DSS
> > elevation indicator taped to the back of the dish.  Great results, blows
> > everything else away.  As time permits, I will remove the existing
feedhorn
> > and move the dipole to the focal point with the downconverter facing
away
> > from the dish, and play a little with the focal point.  Long range is to
> > mount just the 3733 dipole on the C Band 90 degree rotator and move it
for
> > vert and horiz polarization.
> >
> > 2.  Trans 3733 (cut stub) with reflector and 38" X 26" dish. Works well.
> > Dipole located at 12.25" from back of dish.(See above)
> >
> > 3.  "Main" system, Parabolic AB downconverter (Sweden) with Phillips SPG
36
> > antenna.  Longest dimension mounted horizontal.  Works well.  Mounted on
> > roof with az / el.
> >
> > 4.  Scientific Atlanta dish with 3733 (cut stub) without reflector.
Mounted
> > at existing feedhorn location.  Works well. (See above)
> >
> > 5.  I am testing a California Amplifier, Part # 130645, (Ebay)
integrated
> > QLP downconverter, with some of the above noted dishes.  No luck hearing
> > anything yet.  I haven't done too much testing yet with this.
> >
> > I expect to receive a new 2.4 GHZ signal generator this week, and hope
to
> > have something other than subjective results from some of my
> > antenna/downconverter tests, soon.
> >
> > PS:  I am convinced, and others are not, that the computer/soundcard has
a
> > lot to do with recording any blocks of telemetry.
> >
> > Yesterday, I monitored AO-40 for about 3-4 hours on the C Band dish.
The
> > signals were great.  I am an ARES EC and have my own personal small
travel
> > trailer converted to an emergency communications station.  I parked the
> > trailer directly behind the dish to be able to "armstrong" the azimuth
> > rotation.  I used my "Compaq" laptop for the first time, running AO40Rcv
> > 1.22.  Although the signals were "fantastic" as seen on the AO40Rcv
screen,
> > very very few blocks were recorded
> >
> > .  I use an IBM 475 mhz computer with the "main" system in the shack,
and it
> > seems to record everything.  I have used four different computers, and
they
> > all seem to record blocks differently.  YES, I know this is subjective.
I
> > will do additional experimenting as time permits.  I have run AO40Rcv
almost
> > daily since it's debut some four month's ago, and always upgrade to the
> > latest version.
> >
> > FWIW
> >
> > ac9r@amsat.org
>
> --
> Art Goldman
> Logicon Contractor
> NSA Laboratory for Telecommunications Sciences
> (301)688-1719
> ----
> Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA.
> To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org
>

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