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Hi people:
Does anyone could tell me how to calculate the number of turns
required by given frequency? e.g. 2.4GHz. What are the factors that
going to effect the turns? It would be so great if you can list some
reference. Cheers!

There is quite a bit of on-line info on 2.4 GHz helix construction, and we
built two of the versions that have the most complete photo and detail
coverage (33mm and 42mm form dia). Neither worked worth a damn, despite all
the effort put into their construction. Then we built the Biquad, which
worked very well, and finally the can-type waveguide or "Cantenna" was the
simplest and worked the best (use a 3/4 liter can that's 84mm dia, and at
least 145mm long). The helix might be good if you have the ability to
construct a self-supporting bare-wire helix, but the types wound on PVC
pipes with vinyl insulated wire just don't work - - worse, actually, than
the simplest 1/4-wave whip. Use a Wi-Spy Spectrum Analyzer to test
performance with the antenna under test connected to your wireless router. A
more accurate (but more expensive) arrangement is to use the Wi-Spy and an
internal coupling antenna inside a shielded box, with a variable attenuator
good to 2.4 GHz between the antenna under test and the Wi-Spy. Using this
configuration, my results put both the Biquad and 84mm cantenna at +6dB, a
1/4-wave whip at 0dB, a 1/4-wave whip and groundplane at -3dB, and both
Helicals at -7 dB. The Cantenna has better directionality and so was
preferred over the Biquad.

Chuck, W6PKP