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