[TowerTalk] Traps

[Guy Olinger, K2AV]

I would be interested in your take on the probable distribution and
magnitude of power loss in a trapped tribander that has a manufacturer's
rating of 5KW SSB, 2.5KW CW, and 600 watts RTTY. I suspect that the
inner traps on the driven element are taking a beating on 20 meters, but
that's just a head guess of mine.

- - . . .   . . . - -     .   . . .     - - .   . - . .

73, Guy
k2av@contesting.com
Apex, NC, USA

----- Original Message -----
From: Tom Rauch <w8ji@contesting.com>
To: <towertalk@contesting.com>
Sent: Tuesday, July 18, 2000 4:19 AM
Subject: [TowerTalk] Traps


>
> I'm not sure this post will make it through, but here are some
> points we should remember.
>
> 1.) Trap loss will **always** result in trap heating. While high loss
> won't necessarily show up with 100 watts, it will almost certainly
> show up with 1500 watts.
>
> 2.) Trap loss can't be "1 dB per trap" as a rule-of-thumb. The loss
> will vary with trap design, what element the trap is in. For example,
> in a three element antenna with optimum current, the driven
> element traps should have about two to four times the loss of
> parasitic element traps. On bands below cutoff of the trap, the
> traps closest to the boom will have the highest loss. On bands
> above cutoff frequency of a trap, the isolating trap will have the
bulk
> of the loss.
>
> I certainly hope a false rumor like "1 dB per trap" doesn't get
> started. That rumor on par with the rumor we've all heard that
> connectors have a loss of .1dB per connector. These rumors are
> harmful to people, because they cause them to make poor
> decisions...and once they get started they are almost impossible
> to stop.
>
> Keep in mind we went through a similar thing when linear-loading
> started. Now we suffer using less efficient antennas because it is
> difficult to find a well-designed lumped loading antenna.
>
> Now I can't say if some trapped antennas are as bad as measured
> or not, and the problem is most other people can't say that either.
> Without facts from multiple sources, all that happens is a peeing
> contest. So I'll measure some traps, pass them along (I hope) to a
> totally independent source who will also measure them, and then
> we will all know with excellent accuracy how much equivalent
> resistance and reactance the trap has at various frequencies.
>
> A few simple 5 minute measurements of each trap will let anyone
> model the trap in an antenna, and we'll know within a few percent
> how much loss is accountable for in the trap and which trap has
> how much loss. That will be closer than you can rely on a Bird
> meter, and many times better than we can do in any field test of
> field strength or heat.
> 73, Tom W8JI
> w8ji@contesting.com
>
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>


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