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Old February 26th 07, 05:20 PM posted to rec.radio.amateur.antenna
Richard Clark Richard Clark is offline
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First recorded activity by RadioBanter: Jul 2006
Posts: 2,951
Default tuner - feedline - antenna question ?

On Mon, 26 Feb 2007 08:10:49 -0800, dansawyeror
wrote:

I think it may be a common mode problem. There is no choke on the
dipole. I will bring it closer to resonance.


Hi Dan,

One very simple test is to fire up your rig and note the SWR. Patch
in a short, loose length of transmission line to the existing run
(about an eighth wave) and fire up the rig again.

Did the SWR change?

If so, you are being SWR whipped by Common Mode currents.

You can keep introducing different lengths of line until you find 1:1
(unlikely, but perhaps close) and let it go at that. This will be a
single frequency solution, but take care that it does NOT cure Common
Modality. Instead, it adds a vertical component to your transmission
(maybe).

This is not always good as that same transmission line (plus
extension) may run past RF sensitive devices (like intercoms, VCRs,
light dimmers, etc.) that go whacko. It may also fill in the nulls of
your dipole (sometimes good, sometimes bad).

73's
Richard Clark, KB7QHC