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trap losses

To: <>
Subject: trap losses
From: (Pete Smith)
Date: Wed, 3 Jul 1996 03:22:05 -0700
The recent discussion of trap losses in the KT-34XA rang a bell, and I
pulled out July 96 QST, pp 32-34, which describes what purports to be an
improved, low-loss trap design, using parallel coax.  I was surprised to see
that while the trap losses with this design are modeled to be under .04 db
on 10, 17 and 40 meters, they hit 1.66 db on 80, with a trap Q of 171.  The
author attributes this to the antenna's input resistance being "reduced" to
51.8 ohms, and then calls the 1.66 db (for 2 traps) "insignificant."  Huh?

I need some technical enlightenment.  Why are these losses so high?  What's
the relationship between input resistance and losses? What, if anything,
does this suggest about the possible losses in tribander traps?  Has anyone
actually put tribander traps in a test rig and measured the losses?  I'd
sure like to stop conjecturing about the losses and see some empirical data.
I seem to remember that people used to measure the losses in coax at vhf by
running a meaured amount of power into a piece of coax submerged in a
liquid, and measuring the heat rise.  Couldn't the same be done with traps,
particularly with high enough power so that the heat rise would be large
relative to ambient?

73, Pete Smith N4ZR (ex W8QZR, HL9TM, K4FOK, 3B8DT) 

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