With 1500 watts on the antenna, .39 db is a loss of 129 watts.
If the feed Z is 35 ohms, the feed current is 6.54 amps.
Then the effective series loss at the feed is 3 ohms.
If the feed Z goes down, then the effective series loss at the feed
can be even less to produce 129 watts loss, because the current is
higher. Therefore the loss would be *more* of a factor in a parasitic
array, since this tends to lower the feed Z.
Three ohms is really not very much, and the fact that 1/4 waves are
longer on 160, would make this effect more pronounced on 160 vs. other
bands, rather than less so.
I'd think it would be very easy to come up with 3 ohms in the tower.
Zinc plated steel, after all. Under weathered conditions I think it
could be more than that. Particularly bolted together towers with lots
of pieces, subjected to wind stresses.
Now if one could make towers out of hard drawn copper...
73, Guy
 Original Message 
From: "Bill Tippett" <btippett@alum.mit.edu>
To: <antennaware@contesting.com>
Sent: Thursday, March 24, 2005 8:32 AM
Subject: [Antennaware] Realistic Wire Loss?
> I've been modeling my array for 160 and
> was surprised to see a difference in maximum gain of
> 0.39 dB for "Zero Loss" in Eznec 3.0 versus "Zinc"
> for my tower. Does this sound reasonable? I would
> not have expected that much difference on 160.
>
> It's not critical to my model since I am only
> interested in relative differences between the vertical
> with and without parasitics, but I was just curious if
> this difference sounds realistic.
>
> 73, Bill W4ZV
>
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> Antennaware@contesting.com
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>
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