[amsat-bb] 2.4 Ghz Antenna Bridge

[Jesse Morris <w4mvb@xxxxxxxx>]

Good Afternoon,

I'm still going through some growing pains with my antenna bridge. 
Because I had some intermittent problems with the only double male "N"
connector I did all my previous tests with a jury rigged adapter of 2
"BNC" to "N" adapter and a double male "BNC".  Everything looked good
with it when I tested the terminators I have so I used it for all my
previous antenna adjustments.  I did order a new double male "N"
connector however, and when it came last week when I tested the antenna
with the fiberglass supports it did not look as good with it as it had
with my make shift adapter.  As a result I adjusted the grounded link
spacing to the reflector for a null in the bridge with the new connector
and it came out to be about 1/8 inch.  The strange thing is that when I
went back to my make shift adapter it too indicated a good null on the
bridge.  I wont try to explain that because I don't understand it except
to say that the initial difference was not very great and a receiving
test with this antenna compared with PVC antenna with 1/4 inch spacing
showed no difference in signal strength.

At the suggestion of John, G7HIA I did a "rain test" on the two antennas.
 Specifically we wanted to know if water on the PVC would degrade that
antenna as compared with the one with open supports.  When I turned the
hose on the PVC antenna the signal dropped about 2 "S" units but
recovered to normal as soon as I turned the water off.  When I turned the
water on the antenna with the open supports the signal dropped several
"S" units and did not recover when I turned the water off!  I discovered
that the signal strength did not return until I blew the water off the
matching link.  I repeated the test on both antennas several times and
the results were always the same.  Water droplets on the close spaced
link apparently de-tune it much more than on the wide spaced link.

Even though the close spacing may (I repeat - MAY) be a better match the
wide spacing might be a better approach for wet weather.  I did not
perform this test on antennas with the conventional feed but I have no
doubt the same factors will apply.

73 de Jess - W4MVB
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