[sci.electronics] Cross Field Antennas

wwg@brambo.UUCP (Warren W. Gay) (06/23/89)

>[This extracted from INFO-HAMS mailing]
>
>Date: 20 Jun 89 17:31:00 GMT
>From: ux1.cso.uiuc.edu!uicsl.csl.uiuc.edu!gene@uxc.cso.uiuc.edu
>Subject: Crossed Field Antenna
>
>I too, was anxiously waiting for some further information, but hearing none
>I decided to do a little crude experimenting...
>...(The article in Mar 89 "Electronic & Wireless
>World" shows a sketch of the full, balanced version).  My model was only the
>"half" version such as someone said is offered for sale commercially in the
>British Call-book. I happened to have a portion of a 4' x 8' insulated
>sheathing-board (48" x 56")..1" thick and aluminum foil on both sides which
>I used as a ground-plane to tune the "half-model" against. My "cylinder" was
>13" diameter and 15" tall and both ends open. The "disc" was also 13" diameter
>with a 1/2" hole in the center to pass a shielded coax thru.  These dimensions
>were quite arbitrary on my part...just what I happened to have around.
>   Schematically, I used two roller-inductors (28 uh max)...their "hot" ends
>fed the "disc" and "cylinder" elements..one to each..thru short lengths of coax
> (these may break down if you run too much power), and the bottom ends are
>tied together and coupled to the ground-plane thru a "common" pi-capacitor.
> I chose to use the "natural capacitance" of the 48" x56" board for the 
>pi-capacitor (top-foil for ground-plane..bottom foil for common ends of induct-
>ors and feed-point for power in) and it may have been dumb-luck but I was able
> to tune for perfect SWR match (I chose to use 75-meters for testing)...
> to the 50-ohm transceiver coax cable.  The natural stray-capacitance
>of the disc & cylinder (to ground-plane) provide the "C" for resonance at a 
>very high impedance value (thus high-voltage). It appears to me that the only
>way to increase power, is to increase the voltage to the elements. With 100 
>watts, a substantial rf arc can be drawn off either element with a lead-pencil.
>    I placed the foil-board on saw-horses and set the disc 2" above on styro-
>foam spacers,  and set the cylinder 2" above the disc on stryofoam spacers.


I havn't seen the "Electronic and Wireless World" artical, so I'm having
some difficulty with picturing this interesting "beast".  From the 
description above it seems to suggest this (looking at the side):

				+---------------+
				|		|
				|		|	<- cylinder 
				|		|
			?.......+---------------+

			?.......+---------------+	<- disc
	?			+---------------+
	.
	.	+-----------------------------------------------+........	<- gnd plane?
	........+-----------------------------------------------+	.
	(pi cap connection?)						.
								     -------
				   [side view]			       ---
									-

(I'm assuming also, that "sheathing board" is basically styrofoam with
aluminum foil glued/fused to each side)

I'd like to experiment, also, but I'm not sure from the description how
you have wired this. A crude diagram (like above) would help a lot, or
even better, if someone could post one in PostScript code, for a laser
printer.

What have your results been like, when the band is better?  Or, how does
this compare with your long wire/dipole/inverted vee?  You mentioned it
was "weak", so this suggests that it does not do quite as well (at least
the "half" model).


>...Perhaps my observations will stimulate some others to do more
>experimenting on Crossed-Field Antennas.


You bet.  On the surface at least, this sounds like a great new discovery
(who says its all been done on HF already?!).  Please keep us posted as
you continue to use/experiment.  It might be some time before I get a 
chance to -- besides you might save me some trouble :-) :-).  But your
work suggests that there is indeed something real to this-- the matching
is encouraging, but of course the "radiated part" has to be further 
investigated.

73s de VE3WWG