[TowerTalk] Traps and Losses

[Michael Tope]

FWIW, after rebuilding a KT-34XA, I wanted to do a quick
test just to make sure we hadn't made any gross errors
(shorts where we wanted opens and vice versa). I used
a pulley that my friend Robb had rigged to one of the
towers at W6UE to quickly hoist each element from the
KT-34XA up to around 30' where I could run an SWR test
and then pump a little power from the club's Alpha 78
into the element. After 60 seconds key down at 1000
watts and another minute or so to run outside and lower
the element, I detected no evidence of self heating in
the KT-34XA element. Not a very scientific test, but
neverthless it was some indication to me that the linear
loaded trap system in the KT-34XA was reasonably
efficient in terms of I^2*R losses (the linear loading is
admittedly a great heat spreader).

With the help of a second person, the elapsed time from
transmitter key-up to antenna descent would be reduced
to a few seconds. Although, I still think it would be
neat to get hold of one of those infrared scopes. Seems
like that would be a great tool for efficiency testing
of antennas. If sensitive enough, it would also give some
indication of the RF current distribution along the element
vis-a-vis the I^2*R losses (perhaps an STA could be
obtained from FCC to increase measurement sensitivity with
the help of the appropriate vacuum tube technology).

Mike, W4EF................................................

----- Original Message -----
From: "Pete Smith" <n4zr@contesting.com>
To: <towertalk@contesting.com>
Sent: Monday, July 17, 2000 10:34 AM
Subject: Re: [TowerTalk] Traps and Losses


>
> If you look 'way back in the Towertalk archives, you'll find some messages
> from (I think) K1KP regarding his calorimetric tests of a KT34XA trap.  It
> was a homebrew test setup, onvolving a cooler full of water, etc., but
> within some margin of error it seemed to indicate that at least for that
> trap design very little power was being lost in the trap.
>
> It seems to me more likely that the poor performance of trapped antennas
is
> due to the compromises in element spacing that result from trying to make
> the same three or four physical elements work on multiple bands.  I do
> wonder, though, about LB's comment about trap leakage.  It seems as if
> leaky traps could result in some fairly severe out of phase radiation
> outboard of the traps, degarding the directivity.  Anyone know how to
> quantify that?
>
> 73, Pete Smith N4ZR
>
> The World Contest Station Database
> is back up and running at
> http://www.qsl.net/n4zr
>
>
>
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