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Goodbye trapped antennas?

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Subject: Goodbye trapped antennas?
From: (Pete Smith)
Date: Tue, 9 Jul 1996 11:46:17 -0700
At 05:53 PM 7/5/96 -0400, K8DO wrote:

>Now let me repound on the main points.. no one on this list would seriously
>consider making the claim that an Explorer 14 (lambda 0.25) will go head to
>head with a KT34XA (lambda 0.46) for the only SU on the band, long path,  in
>the last sixty seconds of the contest... (at least I hope no one is that soft
>in the head)... yet, the minute you utter the F**** word they start babbling
>about ohmic losses in joints, and traps having light bulbs inside of them,
>and non resonant elements magically doing something, or other... 

It's true that Force 12 never should have claimed that the C-3 (lambda .15
or thereabouts, on 20) "outperforms" all other tribanders unless they were
prepared to back it up with documented test results.  But at the same time,
it isn't impossible that it could compete with, or even beat trapped
tribanders of significantly longer boom length.  The modeling I did on the
C-3 vs TH-7, using N6BV's trapless TH-7 equivalent model - as reported in
the current NCJ- says that TH-7's advantage in gain is on the order of .5 dB
(on 20m).  I just helped put up W9LT's second TH-7, and was reminded again
of how many metal-to-metal mechanical (neither soldered nor welded) joints
there are in the feed system, as well as the 4 traps in each driven element,
and 2 traps in the 20/15 reflector.  It doesn't seem impossible that on 20
meters, where all of those traps are in the circuit, trap losses plus losses
in the matching system *could* account for overall losses of >.5 dB,
effectively negating any gain advantage.  Of course, the superior F/B ratio
would remain. 

Considering the amount of money we spend to put one or two (or 7...) yagis
up in the air in pursuit of 4-5 dB net forward gain, attention to losses
seems very appropriate -- whatever antenna you're using. 
73, Pete Smith N4ZR (ex W8QZR, HL9TM, K4FOK, 3B8DT) 

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