[TowerTalk] Traps and Losses

[Michael Tope]

Guy,

I rigged up a rope and pulley system that allowed me
to drop an antenna element from a height of 30 feet
within a few seconds of having applied 1500 watts.
This would be ideal for testing the self heating hypothesis. If I get some
time, I will put together
my Cushcraft A3 driven element and run this test.

Also, the loss distribution in the typical tribander
will depend on the operating frequency. On ten
meters, one would expect only the inner traps to
play a major role in the overall loss, whereas at
20 meters both the inner and the outer traps will
be active. You also need to consider the current
distribution. On twenty meters, one would expect
the inner traps to be carrying a bit more current
due to the half sinusoid taper in the current
distribution.

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

P.S. An infrared camera might be a neat tool for
looking at antenna self heating "in situ". I know
this technique is used for measuring heat distribution
in PC boards.

----- Original Message -----
From: "Guy Olinger, K2AV" <k2av@contesting.com>
To: <W8JI@contesting.com>; <towertalk@contesting.com>; "Jim Reid"
<kh7m@hsa-kauai.net>
Sent: Monday, July 17, 2000 7:30 AM
Subject: Re: [TowerTalk] Traps and Losses


>
> Good morning, Tom.
>
> Yes, the 200 watt light bulb would get you to a third degree burn if
> held long enough. Of course. Good visceral punch in that line Tom. So
> why don't we have dozens of hams with permanent burn scars to attest to
> the temperature of traps? Easy to explain.
>
> The range test would be satisfied with 4 db of miscellaneous loss or so.
>
> The tribanders I saw had six traps, not one, therefore the loss is now
> smaller per trap. On a hundred watt applied signal, ~60 watts of loss is
> now ~10 watts per trap.  Further, the heat dissipation will now apply
> itself to a combination of surfaces/heat conductors. Depending on the
> exact construction of the trap, both the outside shell, and the element
> into and out of the trap will dissipate heat. 10 watts outdoors over
> that much surface would not even be discernible.
>
> If one got it to operating height, and ran a 1.5 kW signal to it, one
> should be able to discern the heat level, if one could get to the trap
> to measure it. That's a physical problem in itself. You would have to
> run it at some height to make sure it wasn't detuned by proximity to
> ground, and then lower it.
>
> Could you lower it quickly enough to measure heat before it radiated
> away.
>
> Is there any way to measure heat in situ that would not queer the RF
> characteristics of the trap, or not be directly heated by the RF itself?
> Some infrared device with a focusing lens? That's a real question,
> anyone have an idea here?
>
> Truth be known, for the moment, barring some progress on measuring trap
> heat, your assertion regarding the traps is just as precarious on some
> points as the published tribander range testing you downplay so
> severely, hidden behind a difficult-to-measure-without-extreme-effort
> phenomenon. Why should we listen to your objection here if you don't cut
> Ward and Steve any slack?
>
> On the Pro 67 for which I have personal knowledge, the *really* rotten
> band was forty meters, which was traversing SIX traps per active
> element. I think there is a case for ten meters being the least affected
>  by the malaise.
>
> Personally, I would have LOVED for the Pro 67 style design to have been
> right in there with the rest, validated by the study. At one point I was
> going to buy one. The study, however, validates the anecdotal evidence,
> and the advice by an owner and others to buy something else, as he
> disposed of his.
>
> There's just too much anecdotal smoke, Tom. What's the point of placing
> in construction items with acknowledged loss (however one may argue the
> magnitude) when alternative design is available that doesn't require
> them?
>
> Or at the least, why not avoid them in current-heavy elements like
> Cushcraft did in the X7, X9 design. Why did THEY drop the number of
> traps. What do THEY know. More smoke.
>
> Really think there's fire.
>
> - - . . .   . . . - -     .   . . .     - - .   . - . .
>
> 73, Guy
> k2av@contesting.com
> Apex, NC, USA
>
> ----- Original Message -----
> From: Tom Rauch <w8ji@contesting.com>
> To: <towertalk@contesting.com>; Jim Reid <kh7m@hsa-kauai.net>
> Sent: Monday, July 17, 2000 7:51 AM
> Subject: Re: [TowerTalk] Traps and Losses
>
>
> > How silly can we get!
> >
> > That means loss in a trap is about 20% of applied power for a
> > single trap. That means if you had a 40/20 meter vertical handling
> > 1000 watts, the trap would be dissipating 200 watts.
> >
>
>
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