RadioBanter - View Single Post - Even more on antenna feedlines and matching to an antenna.

December 5th 05, 04:53 PM posted to rec.radio.shortwave

wrote:
I've always wondered how this antenna would have performed if the
feedpoint had been in the center as a classic dipole and the xfmr
Z-ratio was different than 1:1. Would this allow some semblance of a
"multiband" antenna as opposed to the direct feed or 1:1 situation
where the antenna essentially is optimum on the primary freq and the
3rd harmonic? Why did I choose the Windom? Because the radio room is
directly across from the 35% length point on the antenna. Even though
it works well I'm not convinced that there is anything "magic" or
unique about the 33 to 35% point on a wire antenna unless there is a
true overall impedance averaging effect when fed at this point. (???)

Frank
----------------------------------
About 10 years ago I experimented 9again) with dipoles for HF.
I tried several different ratios in an attempt to improve recpetion.

I tried a dipole cut for 10MHz and then one cut for 18MHz.
I tried 1:1, 2:1, 3:1, and 9:1.

A 70' "long" wire out performed the dipoles on every frequency, with
every
ratio even on the design frequency with a 1:1.

Of the dipoles, the 2:1 transformer with the 5MHz dipole worked best.
I suspect it worked best because of it's greater length.

The transformers seemed to mainly decouple the coax from the antenna.
If I ever get the time I would like to retry these experiments with
triax or
twinax.

I tried a direct connection with several ferritte cores, but after
reading John
Brynt's excellant article on "Is your Feedline acting like an antenna"
I accept
that I did not have anywehre near enough inductance to supress common
mode effects. I had a LOT of RFI from household devices.

Terry