Re: NEC-LIST: cross field antennas

Golly,

        I have been looking for references to the CFA from time to
time and had not really had much success beyond the original
article(s) by Hately and some rather terse mathematical expositions. I
built a number of CFA's but had much difficulty preventing radiation
from the matching circuits as described.

        I then concentrated on the match of the antenna into the magic
377 of free space by essentially redimensioning the reactive
components ( plates & matching ) so that the antenna represented a
very short ( 5% ) piece of 377 ohm unbalanced transmission line
... except that the fields E x H are 'externalised' ie form a
volumetric radiation surface around the aperture ( for want of a
better word ).

The physical shape of the antenna is very similiar to the original CFA
however one crucial ( in hindsight ) essential physical element has
been added. ( it simplifies the not only the mechanical structure but
also the matching ... and no Virginia it is not a loop.)

I am not sure I should reveal the structural variation to the original
CFA as I have been urged to take out a patent.

The matching circuit reduces now to a 50:377 broadband transformer ie
the feedpoint of the antenna is close to 377 ohms. Current and voltage
maxima at points on the antenna structure are extreme. ( at one point
if a piece of pvc tape is stuck to the antenna structure I can hear
the 'noise' (in a receiver ) it generates when it is peeled off - it
also gives a distinctly painful 'burn' if touched at powers of even 1
- 2 watts )

The antenna has been tested at varying heights above ground from .05
to 1.5 wavelengths at a fixed frequency with no discernable change in
input impedance. ( using RF bridge at antenna feed point )However
signal reports and field strength readings confirmed isotropic nature
of radiation / reception.

All test antennas cut for HF frequencies.

Having said all of that I would point out that the match at 377 ohms
seems to be critical and the matching transformer I use seems to only
give me 10% BW even into my resistive 377 dummy load I built to test
into.

Can anyone point me at a resource for building a 50 to 377 broadband
matching transformer?( it must be able to handle power transmission of
course )

So Pleeeeeeese dont kill off the CFA concept just yet ( I spent too
much time cutting out plates and cylinders in the wee hours of the
morning ).

thanks and regards de VK3PGM.
Received on Thu Feb 11 1999 - 21:30:50 EST