Thanks to everyone who responded on this issue, both to the List
and directly to me. I'll summarize them here,a nd will review them
and post a more detailed summary following the ARRL 160M
Contest this weekend (if I survive).
In brief, the responses said:
1) It'll work, and is just what is done in the Battlecreek Special
(Several folks pointed this out!);
2) The trap must be capable of handling more current than for
the same trap used in an 80/160 dipole (1.41 time the current)
(Thanks W8JI);
3) Don't forget to account for the extra side-stress on the mast
section: back guys recommended (I already use them for the
current 160M Inv-L) (Thanks AD8I....er, W8IK);
4) In my case (45-foot vertical, ~85-foot horizontal) it might be a
good idea to increase the vertical section 5-10 feet, mount the
trap on the mast, and resonate for 80m. Then add the horizontal
wire and tune for 160m (Thanks W8IK).
5) At least one person suggested shunt-feeding the 70-foot tower
instead;
6) Someone suggested sloping a second vertical section up to
create an 80-m vertical or inv-L on the same base;
I'm going to look over the traps I have and see if they can handle
the current requirements for, and if not find plans for a coaxial trap
that I can make.
NOTHING is going to be tried until after the Stew Perry Topband
Challenge!
Thanks all, and I'll hear you in the ARRL 160M this weekend
(if I get the rest of the Beverages installed tonight and tomorrow!).
73,
Jeff Maass jmaass@columbus.rr.com Located near Columbus Ohio
USPSA # L-1192 NROI/CRO Amateur Radio K8ND
Maass' IPSC Resources Page: http://home.columbus.rr.com/jmaass
-----Original Message-----
From: Tom Rauch <w8ji@contesting.com>
To: topband mailing list <topband@contesting.com>; jmaass
<jmaass@columbus.rr.com>
To: <topband@contesting.com>
Date: Tuesday, November 30, 1999 10:44 AM
Subject: Re: Topband: Multi-Band Inverted-L?
>> Long ago I picked up a (hefty) 80-meter trap, intended for a 160/80
>> meter dipole. I'm thinking of inserting it in the horizontal wire with
>> some appropriate trimming to provide coverage on both bands. Am I missing
>> something fundamental here? I've not seen this described in the magazines
>> or books, but it seems like a reasonable configuration. Too much loss in
>> the trap? Won't work at all? 73,
>
>Hi Jeff,
>
>The only catch is the power rating of the trap will be approximately
>half the rating of what it is in a dipole. That is because current and
>voltage in your Marconi antenna across and through the trap are
>about twice that of a dipole.
>
>On 160 meters, the trap in a marconi sees about 1.41 times the
>current in a dipole so I^2 R heating will be about twice as much
>(heating is the problem where the trap operates straight through).
>
>On 80 meters there will be about 1.41 times the voltage, so power
>rating will be reduce by the square of 1.41.
>
>When the antenna is folded in an L this stuff actually gets a little
>worse.
>
>Other than the potential power rating problem, everything else is a
>winner.
>
>
>73, Tom W8JI
>w8ji@contesting.com
>
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