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Tom Donaly · March 6th 08, 11:33 PM posted to rec.radio.amateur.antenna

Michael Coslo wrote:
wrote:
On Mar 5, 3:14 pm, (Dave Platt) wrote:
In article ,
Roy Lewallen wrote:

I highly recommend that you decouple the feedline with a current balun
(common mode choke). Better yet would be two, spaced about a quarter
wavelength apart. Small antennas can be made to look a lot better than
they really are if the feedline is allowed to become part of the
radiating antenna system, so unless the feedline is decoupled well, any
measurements you make will be subject to speculation as to whether the
radiation was from the antenna or the feedline.
It would also be interesting to use a simple current probe to sweep
along the feedline, and see what sorts of currents might be flowing
along the outside of the feedline, both with and without a good
common-mode choke or two in the feedline.

I agree. I think it's quite possible that even a decoupled feedline
will add enough radiation to make the antenna noticeably better
than it really is.
I'd prefer to see the source mounted *at* the antenna to make it
a decent comparison.

But if the major radiation is from the feedline, that will mean the
antenna won't work as it is supposed to.

Since this is voodoo antennaland stuff, the antenna needs to be tested
as Art would suggest, not as we might like. And since most of the chaps
here are a lot smarter than me, I suspect everyone knows that his
antenna just might need that feedline radiation in order to work
"properly".

Now after the initial tests in whatever manner Art dictates, *then* the
feedline should be isolated to determine where the major radiation is
coming from.

At that point, your source at the antenna method is the ticket. That
would remove feedline effects altogether.

Is this test going to be written up somewhere? What is the test protocol?

- 73 de Mike N3LI -

Easier said than done, Mike.
73,
Tom Donaly, KA6RUH