Detailed instructions, diagrams and photos on making a helical antenna for the 2.4GHz ISM band. Suitable for long range wireless networking. The aerial was derived from information on helical antennas in the ARRL Antenna book.
The idea behind this aerial was for anyone to be able to make their own aerial for point to point links, and do it cheaply. The criteria are cost effectiveness, ease of construction and durability. Durability is important as you don't want wind, beak cleaning magpies and highly destructive nibbling cockatoos ruining your Quake III and Unreal Tournament sessions. Birds landing on the aerial have the effect of severely diminishing the signal, too....
Some people (namely some ham radio types who know what they are doing) have built the antenna and found the gain wasn't as good as the theory suggests. I assume that they built the antenna properly and had good impedance matching. This page suggests that helicals could have their gains overestimated by the standard Kraus formula (as used here) by up to 4-5dB. This would have a severe effect on calculated link budgets, especially marginal ones.
Authored by
Jason Hecker at
Homepage, Added: Mar 8, 2004
http://www.wireless.org.au/~jhecker/helix/
