[TowerTalk] How accurate is EZNEC?

[David O Hachadorian]

On Thu, 6 Sep 2001 17:35:28 -0400 "David L. Thompson"
<thompson@mindspring.com> writes:
> 
> Any software is just a tool.  At the best case the software tells 
> you what
> to expect.  At worst case the software at least tells you if its 
> worth the
> effort.   The problem is interaction with other nearby antennas.   I 
> had a
> perfect looking W2PV 24Mhz  3el that fell apart within 7 feet of the 
> KT34XA.
> K6STI had an interacion model that showed promise.  You need both 
> unless
> there is nothing on the tower or nearby (40 feet or so).

There's a pretty easy test for interaction on yagi antennas, once
they are installed.

The yagi characteristic most sensitive to interaction is f/b ratio.
f/b deteriorates much more than forward gain, and, fortunately,
f/b ratio is fairly easy to measure:

1. Have a ham across town transmit a steady signal.

2. Turn the back of your antenna toward him, and note the s-meter
reading.

3. Turn your antenna toward him and crank in attenuators until the 
s-meter matches the original reading.

4.Read the f/b ratio off the attenuator setting.

A precision attenuator is nice, but even the attenuators/AIP built
into modern radios are fairly accurate.

Dave Hachadorian, K6LL
Big Bear Lake, CA
K6LL@juno.com

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