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Re: 2401 MHz beacon advice


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.


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.
> ac9r@amsat.org

Art Goldman
Logicon Contractor
NSA Laboratory for Telecommunications Sciences
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