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Double Helix antenna


I have built up a coaxial dual helix for 1269/2401MHz.  It looks promising
so far, with acceptable VSWRs on each helix for the appropriate frequency.
The coupling between the two helices is -15.4dB at 1269 and -26dB at 2401.   

I cannot easily determine what effects the helices have on the pattern of
each other - tests in the dish will be needed to determine whether the
patterns have been affected to any significant degree to cause a noticeable
degradation in gain.

I have also designed a couple of pcb notch filters, and will be building
them later today.  Simulated data shows notches of around 50dB for one
filter at 1269 (to be inserted ahead of the S-Band converter) and a similar
figure for the other at 2401 (to be inserted between the uplink PA and the

Hope to post some pictures and more details of the antenna and filters on
the website soon.  I'll let you know when the data has been posted.


Charlie G3WDG
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