[TowerTalk] TH7 installed but not resonant

Jim Hargrave w5ifp at gvtc.com
Sun Nov 20 14:52:54 PST 2011


 I would be concerned about the bolt. It could be shorting something out.

I would also have him check the straps from the balun to the driven element.

Also make sure the coax has not pulled out of the connector on the balun.

Its also possible the link between the two driven elements was bent and
shorted together during installation. These tubes cross over between the

    73s de Jim

  > -----Original Message-----
  > From: towertalk-bounces at contesting.com
  > [mailto:towertalk-bounces at contesting.com]On Behalf Of W5XB
  > Sent: Sunday, November 20, 2011 3:02 PM
  > To: towertalk at contesting.com
  > Subject: [TowerTalk] TH7 installed but not resonant
  > Looking for help on my "new to me" TH7DX.
  > Was not used couple of years, cleaned it up, read and used the
  > manual, put it together, and put it on top of an asphalt
  > shingle roof at 25 ft.
  > Checked with MFJ analyzer, and found it resonant low, about
  > 13.7 Mhz as expected. The other bands were low too, but 10 m
  > was about 2:1. It "heard" almost as well as the TA33. Figured, all ok.
  > Due to back injury (lawn mower accident!) can't climb right
  > now, so I had an installer take the TA33 down and put the TH7
  > up on 65' self supporting tower with no surrounding obstacles.
  > Now the antenna is not resonant anywhere. Best SWR is 9:1 at 14
  > Mhz, resistance is 10 ohms, x=57. Coax checks with .9 db loss.
  > The "hearing" is now about nil, like a wire hooked to a piece of coax.
  > Have looked at the antenna with binoculars. The attach points
  > for both driven elements look as they should, but I can't see
  > the gamma match from the ground.
  > The installer is not familiar with the TH7, but has put up
  > dozens of SteppIrs, and monobanders. He did mention something
  > about "adding a bolt near the Gama match tubes" ... not sure
  > what he did. Boom support is Philly Strand.
  > Will of course show installer, the assembly manual and ask
  > about the added bolt.
  > Installer is coming back Monday afternoon to check out.
  > Any clues about what to check, greatly appreciated!
  > Many thanks and 73s,
  > Grant
  > W5XB
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