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I want to use a ~265 foot horizontal 80m closed loop, on 160m
what I need/want to do is
open the far side of the loop when it is operated on 160m
and close it for 80m and above
how do I do that?

the loop is and has to be coax fed
not a situation where ladder line can be used!!!!!

TIA
ka5oai

Install a 160 meter trap at equal distance from the feed point (half way
around the perimeter) of the loop.

73 Glenn K4DTT



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Sam wrote:

I want to use a ~265 foot horizontal 80m closed loop, on 160m
what I need/want to do is
open the far side of the loop when it is operated on 160m
and close it for 80m and above
how do I do that?

How about a 1/4 wave (at 160 m) shorted stub of transmission line across the far end of the loop? A balun and a ~30 meter roll of coax could be packaged up pretty small, compared to the size of the loop.

K4DTT@... wrote:

Install a 160 meter trap at equal distance from the feed point (half way around the perimeter) of the loop.

that part I understand,
it's what the trap consists of
and how to calculate and make it that I'm asking about.
--
GB & 73's
KA5OAI
Sam Morgan

_ ()
Here is a site that describes the trap thing very well. I cannot find the QST
article that I was thinking of when I first posted to you. Good luck and
great fun.

73 Glenn, K4DTT



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I don't know about the stub but I am sure the trap will cover the band as it
seems to be rather low Q. I haven't tried it.

73 Glenn K4DTT



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K4DTT@... wrote:

_ () Here is a site that describes the trap thing very well. I cannot find the QST article that I was thinking of when I first posted to you. Good luck and great fun.

thanks for the info, defiantly a big help.

using hamcalc
for 1.9mc
I come up with
a ~15 turn coil of RG-58
on a 3.5" coil form
using ~13' of coax
and the 80m loop needs to be shortened by ~ 13'

I have had other replies that mentioned
using an open 1/4 wavelength stub
using RG-58 that would be ~ 128'

am I on track here?
would either way work?
is one way more narrow banded than the other?
meaning if I made this for 1.9mc
would it still work at 1.8 or 2.0mc?
--
GB & 73's
KA5OAI
Sam Morgan

Sam Morgan wrote:

using hamcalc
for 1.9mc
I come up with
a ~15 turn coil of RG-58
on a 3.5" coil form
using ~13' of coax
and the 80m loop needs to be shortened by ~ 13'

These lengths sound short to me.

I have had other replies that mentioned
using an open 1/4 wavelength stub
using RG-58 that would be ~ 128'
am I on track here?
would either way work?
is one way more narrow banded than the other?
meaning if I made this for 1.9mc
would it still work at 1.8 or 2.0mc?

I think a 1/4 wave shorted stub would be wider band than a half wave open stub. The open stub is also prone to arching from the high peak voltage at the open end during transmitting.