RaDAR – The Prodigal Son

For quite a few years now I have left the standard dipole in search of a truly rapidly deployable, multiband, effective, antenna for use with RaDAR.

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I have tried open wire fed, random length dipoles, various configurations of the W3EDP, delta loops (good), open wire fed delta loops, manually tuned end feds (good), The FUCHS multiband end fed, wire J-Poles (they work) the ZS6U minishack special and also the ZS6BKW multiband open wire fed dipole (similar to the G5RV) not to mention the 9:1 UNUN fed long wire (multiband but shocking!).

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The closest to my goal, for specifically RaDAR, were the resonant length end feds, especially the single band manually fine-tuned ones (they work WELL and the earth / counterpoise is not that much of an issue).

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I guess what brought me back to reality was seeing the SWR as the AT-897 ATU tuned the 9:1 UNUN fed long wire during the recent African DX contest. SHOCKINGLY HIGH SWR. OK I have worked DX running QRP with this antenna but things don’t look quite as right as they could be!

My thoughts returned to the link dipole (I had tried one once too) and I drew up a chart of calculated resonant lengths for an inverted vee. Being RaDAR, it’s quite unlikely that the antenna ever be deployed as a dipole, that’s just not going to happen, so the lengths were calculated as if the antenna would always be an inverted vee.

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I built the antenna this weekend. It took me a while. Although not quite the best for RF, I used crimp on bullet connectors. I might add that the crimp on idea works great for RaDAR if you want to put something together quickly in the field!

I did a few SWR tests last night and found one or two places where I had measured incorrectly and after trimming, I had perfect SWR on my FT817ND’s meter. The antenna is rapidly deployable and will fit together pretty nicely with my painters pole RaDAR mast.

Rolling up the antenna when packing up was always an issue but I included a facility using chopping board where the coax meets the antenna. I guess I could have made it more compact but the general idea seems to work OK. The next one I will build will include all the improvements I may see fit while doing actual deployments.

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All ready for next weekend’s summer QRP contest!

73 de Eddie, ZS6BNE

 

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