Jean-Jacques / ON7EQ performed some tests
on helices, not directly related to WLAN, but on AO-40
Amateur Satellite communication at 2401 MHz. As it is basically the same
frequency band, it is interesting to know his experiences. The
original 40 mm PVC Helix design tried, resulted in a weak reception
of S5 for one single Helix. A single 32 mm PVC helix did about S7.
Following is an abstract form the e-mail of
Jean-Jacques to Jason, Remco and myself:
" The optimal design according to PA0HOO
is about 67% from 'AIR' values, resulting in space between windings of
So, just to doublecheck this theory, I
quickly constructed a new 'test' helix on 32mm OD PVC pipe, still with
the triangular matching stub (using 71x17mm original dimensions) and
same 2.5mm˛ solid copper wire. The lenght of the helix was same (80 cm
about). Reflector 130x130mm stainless steel plate.
Result with this helix design were much
better than the 40mm version ! The beacon was now about S7,
with fading and noise, but a lot better than the 40mm version. The fact
that this antenna was performing better was confirmed as well by the
fact that is was much more directive as well....
Personally, although the Wavelan enthousiast 'down under' have apparently
achieved excellent results with helixes wound on 40mm PVC (even quoted as
INNER DIA, making it worse than my 40mm OUTERr dia pipe), I got the
impression that the 32mm version works much better (according to my
'ear', my 40mm version provided certainly 3 to 5 dB less gain than
the 32mm version). Maybe this is compensated by a wider turn spacing (42mm
instead of the theoretical 33mm) used in the design of Jason?? From my
end, I would definitely recommend to build them on 32mm pipe !"