RE: [amsat-bb] S-Band Antenna Comparisons, etc.

["Steve Diggs, W4EPI" <w4epi@xxxxxxxxxxxx>]

FWIW, the specs says the Conifer 26T-2400-1 antenna (the one K5OE tested)
has a beamwidth of 7.5 degrees.

Regards,
Steve Diggs, W4EPI

-----Original Message-----
From: owner-AMSAT-BB@AMSAT.Org [mailto:owner-AMSAT-BB@AMSAT.Org]On
Behalf Of K5OE@aol.com
Sent: Sunday, January 07, 2001 11:30 AM
To: amsat-bb@AMSAT.Org
Subject: [amsat-bb] S-Band Antenna Comparisons, etc.


I did some antenna experiments this AM when AO-40 came over my horizon (1200
utc, MA=4.5).  Those window-shopping the various options may be interested
in
these observations.  What can be determined from current observations with
respect to the final satellite configuration is subject to considerable
speculation:  these observations were taken with a squint of greater than
140
degrees on AO-40's low gain antenna at low power.  What one can extrapolate
to a favorable orbit, orientation, and squint, plus the change to the
high-gain antenna and the high power amplifier, is clearly just speculative
at this time.

In a quasi-designed-experiment, I used several antenna and downconverter
combinations using a Drake 2880 and my Yaesu FT-100 as a receiver, and
recorded the results enumerated below.  One unknown in my measurement system
is the accuracy of the meter on the Yaesu.  I have previously "calibrated"
it
using a variable power 2 m FM signal, but only in the crudest sense (after
all, I am an "amateur").

1.  The 24 dBi dish antenna (bar-b-que style, borrowed from KK5DO), does
indeed offer a 12 dBi gain (2 full S-units) over my 16-turn helix (estimated
at 12 dBi).  This was consistent with-and-without a preamp.  Note to those
without automatic antenna tracking:  this antenna's beamwidth was so narrow,
that 12 dB of signal was lost in +/- 5 degrees of movement.

2.  The Conifer preamp does NOT provide the rated 10 dBi gain, but appears
much closer to 6 dBi (when close-coupled to the Drake).  It was difficult to
judge the impact on S/N ratio with this setup, but I believe it was
substantially improved, even though the noise floor is up 6 dB as well.

3.  At MA=18, I could detect the beacon with a coffee can and preamp/Drake
combination, but it did not move the S-meter.  I could not hear the beacon
without the preamp.

4.  Using an unmodified Drake 2880, I could not detect the beacon at 121.3xx
MHz with both the dish and the preamp in line.  This surprised me.  If I
have
the frequency conversion for the stock crystal wrong, please let me know.

5.  In comparing the 16-turn helix I have been using for a month to a much
smaller one built for me by my friend Oleg, RV3TH, the two were fairly
comparable.  The interesting thing is that helix is only 7-turns!   Oleg's
helix employs some non-conventional metrics:  the diameter is about 44 mm
and
the turns spacing is about 37 mm, plus it uses a 100 mm semi-parabolic
reflector.  I will report more on this after I completely reverse-engineer
it
:-)

For those interested in seeing the hardware, I have put a few pictures of
this equipment at:
http://home.swbell.net/k5oe

73,
Jerry, K5OE


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