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2.4 ghz Antenna Bridge



Good afternoon,

Thanks to all who responded to my questions about the antenna bridge.  My
unit is apparently not operating properly yet.  The "fix" that I made is
apparently some sort of end run around the problem.  I absolutely can not
get it to null unless the meter port is terminated with some resistance. 
Even so, using a current meter the bridge works well enough to adjust
antennas, check terminations and do a lot of other neat things.

I re tested the three antennas outside this morning before the rain came
and I am still not able to detect any difference in them. I believe the
W0OQC grounded feed works just as well as the conventional feed.  I did
however, explore a point that makes my previous gain measurements
suspect.  The 3 lb coffee can (it's actually 2 lbs 7 oz) I was using for
comparison has a squint of about 30 degrees in the direction of the feed
probe.   In other words if you have the probe vertical in the top of the
can, max signal is received when the can is tilted up about 30 degrees. 
If the feed is horizontal and in the right hand side of the can then max
signal is about 30 degrees to the right.  If I compare the 21 turn helix
antenna to the coffee can with both on axis the helix shows up at about 4
or 5 db better than the coffee can.  If I adjust the coffee can for max
signal they are about the same.  So I can say for sure that 1) the helix
is 4 or 5 db better than the coffee can and if the coffee can is around
10 dbi gain then the helix is close to what it should be considering 3 db
for polarization mismatch or 2) the helix and the coffee can are about
the same so the helix is 4 or 5 db worse than expected.  I tend to
believe the latter.  As they say, you mileage may vary.

I would like to build a helix like the one described in the antenna
bridge article but I have not found any suitable supports for the helix. 
Can someone elaborate on the fiberglass tubes referenced in that article
or perhaps suggest something else suitable.  What about the carbon fiber
arrow shafts?  Is that metallic or is it plastic based?

Thanks for the help.

73 de Jess - W4MVB

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