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Portable 28 MHz (10 Meter) 2 Element Beam by KL7JR/VE8RST/VY1RST The old standby 102 inch steel CB
whip has been around for a long time and used on the amateur bands
by many hams over the years. This design will incorporate four of
the steel whips and allow us to concentrate our signal to a specific
area and give us 3 to 4 dBd to boot (*)! It is
direct feed with 50 ohm coax. It will also be easy to
assemble and fairly transportable at a cost of about $100 depending
on how you connect the whips to the boom or use new or used
materials. Here's a method I chose which will make it a snap to
assemble and install in cold weather, field day, etc.
Now, keeping that in mind, and trying to maintain the 8 ft and 6 inch length of the CB whips (I didn't want to cut the whips down as I may want to reuse them some day for other projects) we find these dimensions (trial and error using the above antenna calculator): for 27.8 MHz the driven element is 8 ft and 6 inches long (the actual length of each whip+-) on each side, and the reflector is 18 feet long (**) with a spacing of 6 ft and 9 inches. The difference in the desired frequency of 28.450 MHz vs. the "not to cut the whips" frequency of 27.8 MHz is only .650 MHz which should be easily handled by any antenna tuner. To mount the whips to the boom, you
can u-bolt a short piece of "L" channel (+- 6 inches long with the
predrilled holes) to the boom and then mount the antennas to that
using insulated connectors for the driven elements and non-insulated
connectors for the reflector.
The 102 inch steel whips are available from DX Engineering (#DXE-WP-102) or through Radio Shack (?). This design may also work on 12 meters as well. This antenna is in the experimental stages, but the above dimensions should be good starting points, and you may chose to cut your whips down to the design dimensions above. Keep in mind that whether or not you use the commercial mounts on the reflector, or your own mechanical design, that you will have to make certain both whips are connected together forming one continious electrical connection. Other wise it will not work! If you have trouble tuning for lowest swr or just don't want to bother, then use your tuner. A 1:1 balun at the feed point is also suggested. Any and all feedback is appreciated. 73 de Yukon John, KL7JR kl7jr at Yahoo.com *See "2 Element Wire Beam for 28 and 24 MHz" on this website ** You can add 6 inches of wire to each of the 102 inch whips to get the 18 ft length, or not. Experiment either way. Powered by Ham
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