[Antennas] coaxial trap

[Ed - K9EW]

Hi Glen,

I just read your post about the trap flash-over.  It sounds like
you're using a coaxial trap as an open circuit on 80m in an inverted-L
antenna for 80m and 160m.

Something you might look into is to use the coaxial L-C (I'll avoid
calling it a trap) so that the antenna operates on both bands without
using the parallel - resonance of the L-C on either band.  This will
avoid applying power to the "trap" at it's resonant frequency where hi
voltages and currents will exist.

Instead, you use the "C" part of the L-C to shorten the electrical
length of the antenna so it will be resonant on 80m.  And use the "L"
part of the L-C to electrically lengthen the antenna so that it will
be resonant on 160m.  Note that in both cases (160m and 80m), you are
using the entire length of wire.

I have seen references to this design, but I'm afraid I cannot
recommend any of them because they're not specific enough to do a
design (sort of like my email).  I was surprised (and disappointed)
that the ARRL publications didn't have any specifics either.  But
maybe someone on the list can help us both out with an actual design
procedure for this type of antenna.

Hope this is of some help.

73,
ed - k9ew

On 4/24/07, G B <microsys at alltel.net> wrote:
> Well, some bad news on my inv L with a 80M trap.
>
> I used the amp for the first time two nights ago on 80M.
> Everything was fine for a little while, tuning up, with very low
> swr, around 1.2.
>
> Well the trap failed with high power.
>
> So, I guess i must recommend that you do not use rg8x foam for a trap if
> you plan on high power.
>
> I changed the trap to some old rg8 I had laying around and it handles full
> power without a problem.
>
> 73's
>
> Glen K4KV
>
>
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