Slim Jim UHF antenna dimensions/design

As per my previous post the antenna went under many tests! and actually it proves itself as a very good antenna which can be placed even on a mountain RPT due to its small size. Bellow you will find the dimensions of the antenna that i built and it tunes CF @ 436.000Mhz.

Schematic 1




BW 430MHZ-440MHZ with less that 1.4/1 SWR - 1.1/1 SWR at the CF and Z=50Ω

A. 50.3cm
B. 33.1cm
C. 16.6cm
D. 1.7cm  D=A-B-C
E. 0.7cm
F. 1.5cm

You might have to lengthen by 1cm element C! It depends were you want to tune the antenna. Also below you will find an approximation on were you have to feed the antenna.

Schematic 2

To tune the antenna you have to place it on a plastic pole not contacting the metal mast. Then you should install it to an open space as this type of antennas are very sensitive to objects and metal surfaces even you!!! So will you are tuning stay as far as possible. To tune the antenna you have move up and down the feed point so you can find the sweet spot of Z=50Ω were SWR will be low. If you cannot find it then possibly you will want to increase or decrease the length of C. For sure an antenna analyzer would be handy and make your tuning a walk in the park but if you do not have an antenna analyzer you can use a good quality SWR meter.
In my next post i will discuss the Super J Pole antenna for the 70cm band, which i have to tell you from now that i works great!!!

73

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