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[TowerTalk] Any thoughts on a Hy-Gain AV-640?

Subject: [TowerTalk] Any thoughts on a Hy-Gain AV-640?
From: K8RI on TT <>
Date: Thu, 01 Sep 2011 01:52:41 -0400
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I've had very good luck with the Hy-gain AV-640, BUT after the wasps 
built a nest in the matching network and the connector was filled with 
"Bee Goo", I've never been able to get it quit right or at least not to 
stay right.

Initially I replaced the compensating cap (bout 47 pf) and clipped out 
the shunt inductor which was fried!.  That worked and I replaced the 
shunt inductor. The shunt inductor is only for protection and puts the 
radiating element at DC ground. The Xc of the compensating cap *should* 
cancel out the reactance and put the SWR right at 1:1 or very close. 
Originally it was at 1:1 at resonance on all bands 40 through six.  At 
least it worked for a couple of months but then the SWR went back up and 
I gained a number of *extra* resonant points around each band...again.

I took the matching network out of a new AV-640 and installed it on the 
old antenna.  No improvement.  It could be a poor connection on the 
antenna but 40 meters which uses everything except the stubs works just 
fine.  This leaves me with the possibility of the coax from the antenna 
to the remote antenna switch, or something in the antenna itself.  There 
isn't a whole lot that can go wrong with the AV-640 as it has no traps. 
It has IIRC two loading coils near the top and 3 capacity hats.  It 
could be a poor connection, but I've not been able to find one and a 
poor connection on the radiating element should affect 40 meters.

I have shorter lengths of LMR400, LMR600, and Davis Buryflex I can 
substitute for the current feed line back to the remote switch.  I've 
already eliminated the switch by using the different feed line out of 
the shack/shop to the current line that runs to the antenna and 
bypassing the remote switch. That just leaves the coax and connectors 
plus the radiating part of the antenna.

I have the new AV640 nearly assembled so I hope to be able to substitute 
it in place of the old antenna by tonight.

So, first the substitution of the feedline with connectors and then the 
substitution of the radiator which is a lot of work.

I really expected to see the thing work when I replaced the matching 
network, but no go.

Any thoughts that I may have missed.

As a side note, the AV640 is mounted on a 24' length of 2" 6061-T6 with 
a 1/4" wall that I can easily raise and lower onto saw horses where I 
can make adjustments.  It's just a bit time consuming and annoying.


Roger (K8RI)


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