[Antennas] antenna modeling request

2002年4月22日 21:56:44 -0700

I put together a model following Gary's request: this is a 5-turn horizontal
helix, with 100' circumference
turns, about 12 feet above real ground. It's fed via 33' of 300ohm balanced
feeder connected to the
two ends of the helix. Because it's getting entirely too late here, the
loops are modeled using octagons
and Gary's 5-core conductor has been modeled as Al pipe of 1/2" radius.
Performance:
freq R jX dBi angle
3.800 3.1 -385 -4.4 86deg.
7.050 47.5 -217 7.09 89deg.
14.150 168 -741 5.07 74deg.
21.200 340 77 6.45 50deg.
28.500 674 485 5.07 28deg.
Looks nice from a matching point of view. Not so nice from angle of
radiation point of view
but you aren't going to get much from any horizontally oriented system this
close to the ground.
These results were obtained by using MMANA - a free antenna analysis program
for hams.
It can be downloaded from http://www.qsl.net/mmhamsoft
There's also a yahoo group: MM-HAMSOFT - that services this and other ham
s/w from the
same source. MMANA takes a little getting used to, but it's pretty neat
once you get into it,
especially the optimization stuff.
--ian k3imw/6