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Old June 1st 11, 02:13 AM posted to rec.radio.amateur.antenna
John S John S is offline
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First recorded activity by RadioBanter: May 2011
Posts: 550
Default Relation of radiation resistance and terminal resistance

On 5/31/2011 7:48 PM, John S wrote:


The coax (right side) is connected as usual to the BNC and bent as
shown. However, the coax's center conductor *only* is connected at the
top to the #14 wire on the left of the diamond. The bottom end of the
#14 wire is connected to the BNC connector shell at the bottom.

The piece of coax on the right forms the balun. It is close to 1/4W
internally considering the velocity factor of the coax, but about 1/2W
externally.

As I said, it isn't exact. It measures very well here. I measured VSWR
of 1.02 but that was not the important part of all this. I have yet to
measure current on the transmission line from the BNC to the source to
my satisfaction.

If I can supply clarifying info, let me know.

73,
John



I meant to give Walt (W2DU and Reflections III) credit for the inherent
balun as before. My only contribution is my discovery (or re-discovery)
that the terminal impedance of the antenna can be adjusted within the
limits mentioned in my earlier post.

One other post script: As the quad departs from a square, it seems that
the antenna gets a bit more touchy with regards to dimensions. It is
difficult to tell for sure, though, since I'm doing this at 434 MHz and
*everything* is touchy there.

Cheers,
John