THE 20 METER "WONDER BAR ANTENNA"
This 20 meter Wonder Bar antenna project is based on the work by W5ECP
The antenna is bi-directional with very little radiation off the ends making it suitable for use with a rotor.
If you have seen the 10 Meter Wonderbar project on this web site, then as a comparison of size, the 20 meter Wonderbar, is about 2 times larger overall.
This article should not be considered here as a "construction article", but can be used to give you a better understanding of how the antenna is designed. The final actual "construction" of the antenna will have to be left up to your ingenuity.
117 / 14.15mhz = 8.26 feet per arm. (14.15mhz was the original design frequency in 1957 article in QST) This will be very close for experimental purposes and any small difference can be adjusted using the tap point.
The article and resulting research did not reveal the "angle" of the arms relative to any reference point but did say that the arms are "spread" so that the ends would be 5 feet apart. This does not exactly agree with the length of the connecting wire in the drawing above, between the arm ends, so it would be assumed that the wire length connecting the arms would be at least 5 feet! It is also assumed that the angle would not be extremely critical. The main elements were made from aluminum tubing in the original article published in QST. 3/4 inch aluminum tubing was used in the original.
Coil winding and tap point details.
The main coil consists of about 30 turns, close wound, of #12 insulated wire on a suitable 1 1/4 inch diameter non-conductive form such as Lucite, wood, PVC, etc.
The tap point is made by attaching a wire from one half of the "delta" loop section to the main coil at the lowest swr point determined by experimentation.
In the original article, only 13 1/2 turns of the main coil was used to resonate the antenna at 14.15mhz test frequency. The other 17 turns are shorted. According to the article, fewer turns can be used on the main coil, say 15 to 20 and still allow ample room for swr adjustment. Some experimentation will have to be done to determine the exact tap point on the main coil for lowest swr and this point appears to be critical in the adjustment!
The original article stated that the antenna was used at 25 feet above ground with good success and that it should be "aimed" broadside to your desired direction. If a rotor is used, you only need to turn it 180 degrees to change direction.
Many thanks go to Ken - KD0AGV and Dave - N0EOP for their valuable assistance with the research for this article!
Hamuniverse.com uses Green Geeks Web Hosting!