Cushcraft's traps have been the problem with many of their antennas from
what I have seen. Their inability to come up with the simplest of idea to
label their traps is down right criminal. Getting just one wrong screws up
the entire installation. You would have thought that someone would have
taken them to task on this by now. At any rate, I had to borrow a grid dip
meter to get the ones on my A-4 correct back in 1998. Others may have
ideas...I have heard of doing it with an MFJ-259. But for the lack of a
better idea of what might be wrong with your antenna you might look at the
possibility that one ( or more ) traps is in the wrong location. Good luck.
- Mike
-----Original Message-----
From: towertalk-bounces@contesting.com
[mailto:towertalk-bounces@contesting.com] On Behalf Of Robert Chudek - K0RC
Sent: Monday, November 02, 2009 10:19 AM
To: towertalk@contesting.com
Subject: Re: [TowerTalk] TowerTalk Digest, Vol 83, Issue 4
This is a used antenna purchased from a -sk- estate, so the original
performance is unknown. The antenna had been stored for a couple of years
prior to installation a few weeks ago. The dimensions were triple checked
during reassembly. Before installation it was "stood on end" with the
reflector on saw horses and the tuning appeared correct at that time. There
are no nearby objects and it's the only antenna on the tower at this point.
This isn't MY antenna at my qth though. It's being installed at a qth about
150 miles away so this is second-hand feedback from the owner / installer.
What I have learned while trying to help troubleshoot the problem is most
suggestions come from the manual... wrong section lengths, bad traps,
interaction with other antennas.
What I have read while searching the internet is Cushcraft did a poor job of
labeling the traps, so it's possible to install them in the wrong position.
Someone also claimed that traps could be installed "backwards". Because a
trap is a parallel L & C circuit, I can't see how a trap could be
"directional". I believe this is "folklore" that belongs with some of the
other urban legends floating around in the ham circles. Without physically
inspecting the antenna I don't know if this is even possible.
A few fellows sent me their VSWR readings so I now have a basis for
comparison for this antenna. I sent this information up to the fellows who
will be taking the antenna down tomorrow for inspection. They are
considering bringing the Driven Element down by itself in the belief that it
is the culprit.
Here's the next question: If you have a properly tuned and functioning A3 or
A4 with VSWR curves that dip at 14.100, 21.200, and 28.500... if you remove
and isolate the Driven Element will its resonant frequency be affected? In
other words, do the parasitic elements shift the DE resonant point when its
tested as a dipole? Has anyone done this and measured the results?
To be continued...
73 de Bob - KØRC in MN
------------------------------
Message: 8
Date: Mon, 2 Nov 2009 09:04:50 -0500
From: "Michael Ryan" <mryan001@tampabay.rr.com>
Subject: Re: [TowerTalk] Cushcraft A4 VSWR curves
Cc: <towertalk@contesting.com>
Message-ID: <000e01ca5bc5$719fbf60$54df3e20$@rr.com>
Content-Type: text/plain; charset="us-ascii"
New or used antenna? Re-assembled?...just curious. - Mike
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