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
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