Allan Greening, VK3PA wrote:
Sent: Saturday, April 05, 2008 3:48 AM
Subject: Topband: 4 square array
> when using short verticals for my 4 square (90 foot x 3 inch dia alloy
> tubing), should i use 4 guy wires or 3.. i am using 43 foot of wire for
> the top guys as top loading, so will 4 be better than 3 as fair as top
> loading goes.. i 'spose the Q is? everthing is ready to go up es gnd
> radials r in, anyone got a spare back hi hi..de vk3pa
Allan & other Topbanders:
Based on the information Allan gave me of using 3 inch irrigation tubing
with four 43 foot top loading wires at the 85 foot level sloping down at 45
degrees, I was able to load the data into EZNEC 4.0 and found the
configuration, assuming series feed at the base, gave me a resonant
frequency of about 1.62 MHz where Z ant = 17 ohms.
This configuration at 1.82 MHz results in
Z ant = 25.2 + J67 ohms, so approximately 1300 pfd series capacitance is
needed to tune out the inductive reactance at the feed point for each
vertical.
Alternately, using four 30 foot top loading wires at the 85 foot level,
again at 45 degrees down slope, gives:
Z ant = 23 ohms (23 + J0) at about 1.823 MHz.
This eliminates the series capacitor.
Since Allan intends to use a Comtek phasing box, direct series feed with 1/4
wavelengths of 50 ohms coax to the phasing unit should work well, with the
resulting impedance transformations.
GL & 73,
George K8GG
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