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RE: A naive helix/dish question



Hi Freeman

> I am at the point I need to consider how to mount the 5 1/2 turn helix I
> have.  The question I have is, do I mount the helix so that the far end
> of the helix turns or the ground plan of the helix is at the focal
> length of the dish?

Rule of thumb at 2.4GHz is that the helix phase centre is about 1.5" or so
in front of the helix reflector. Don't beat yourself up about this - +/- an
inch or so won't make much difference.

> Also, are dishes and helix as easy as G3RUH makes them out to be?

Yes, once you've had the practice of making a few dozen ;-) Check out my
page on making helices at http://www.g6lvb.com/60cm.htm and
http://www.g6lvb.com/quadruple_helix.htm. Although the latter applies to
twenty turn helices, the same tricks are used for smaller ones too.

The beauty of helices is that they are broadband and so are fairly tolerant
of aberrations. The exception to this is any matching arrangement that is
intolerant to apparently small measurement errors at 2.4GHz.

73 Howard G6LVB
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