The example you quote, C19 and 340N, is probably an exception that
proves the rule. In general I agree with W8JI's assessment. These two
antennas, though, carry time spent in *developing* an independence that
would never occur otherwise except with blind luck.
The effect of "shadowing" would require closer elements than present on
the 340. The real interference, if it occurred with a pair like this,
would result from the outcome of all the 340 elements being present in
the *near* field of the tribander.
In that case, the way to examine all the reactions is to add up all the
vectors, compute the currents, e.g. model the interactions, with due
attention to the difficulty of modeling linear loading. Ante up and get
your NEC 4 license....
-----------------
Guy Olinger, K2AV
Apex, NC, USA
----- Original Message -----
From: Pete Smith <n4zr@contesting.com>
To: <towertalk@contesting.com>
Sent: Monday, January 29, 2001 9:30 AM
Subject: [TowerTalk] Shadowing of small antennas by larger ones?
> Mechanical and wind-load considerations aside, is there a significant
> gain/pattern problem with placing a significantly larger antenna above
a
> smaller one on the same tower? For example, consider a Force 12
C-19XR
> tribander, with a Force 12 340N 40-meter antenna (elements roughly 85
> percent of full size) mounted 12 feet above. Force 12 states that
> interaction is no problem because of the design of the N elements. If
that
> is given, then I wonder if there are other considerations. Would the
big
> antenna, by its presence, interfere with pattern formation or gain, by
what
> some people call "shadowing." Or is that just another urban myth?
>
> 73, Pete N4ZR
> Contesting is!
>
> The World Contest Station Database
> is waiting for your input at
> http://www.qsl.net/n4zr
>
>
>
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