View source for Accessories:G7RGQ Omni Directiona Antenna

For a long time, until I got the russian wonder, I was using this [http://www.kineticavionics.co.uk/forums/viewtopic.php?f=1&t=7489&sid=a97d41478e66511dd5cf715ee7c88df0&start=24 antenna] but with quarter wavelength radials only. Don't know what the author hopes to gain from longer ones, within 30 years of ham radio life I never saw radials different to half wavelength. I have measured one on a network analyzer. If you leave the antenna rod in free space (as in the picture below), make the top section about 2 mm longer, if you put a 20 mm plastic tube over it, shorten the top section by 5mm. I do not know the influence of a wide diameter (50 mm - 100 mm) plastic tube, maybe this is then just matching the given length.

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Click on the pictures for higher resolution (drawing from orignal web page, in order to copy before it disappears there)

A final note for manufacturing: Take a long wire and put markers for the sections on it: 136 mm -> 65.5 mm -> 205 mm -> 65.5 mm -> 190 mm.
Then '''first''' roll the inductors (1.5 turns onto a 9.5 mm drill) and '''second''' do the 90° bends in order to get it straight.

Another good antenna, which is easy to build (you may leave away the loop with acceptable degradation) can be found on [http://www.lll.lu/%7Eedward/edward/adsb/antenna/ADSBantenna.html Edward's page].