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Re: 2401 MHz beacon advice



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

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