Okay. Let's try to simplify my situation.
Storm cloud are visible, so I don't have time to buy teflon coax and wind an
awesome choke, mount it in a box, install SO-239s, etc. I DO have 12-gauge
THHN, but I don't have the time to source a workbox and install connectors
right now. In the spring this will all be redone properly, as the antenna will
be moved to a taller tower, etc.
Think of this as a post-apocalyptic scenario. No shopping. No non-zombies with
whom to trade. Etc. Just what I have on hand.
I have a hexagonal beam on top of a 22-foot tilt-over tower. At the base of the
tower I have a weather-resistant box that houses a terminal strip (for patching
my tower rotator cable to my shack run of rotator cable) and a UHF bulkhead /
union, for patching my tower coax, which includes a rotator loop AND a ferrite
core, to the length of larger coax that runs back to the shack.
The tower coax is RG-8X or LMR-240. Including the choke and the rotator loop it
will be 30-35 feet long.
So, with storm clouds visible and no time to shop or build the best possible
choke, what do I do?
I have a length of coax, and I have an FT-240-43 or an FT-240-31. How many
turns? Solenoid or bunched up? Tightly wound or turns of a couple inches?
Experts get set. Experts get ready. Experts GO!
Thanks. :)
--Kirk, NT0Z
P.S. LUV the cold-WX signal boost that I have historically enjoyed...but as I
approach my early-onset curmudgeon phase, I'll take the T-shirt WX we're now
having in MN (2 days only).
P.P.S. The hexagonal beam manufacturer sells / recommends a sleeve balun made
from a bunch of ferrite cores slid onto the coax near the antenna's feed point.
That may indeed work from 20-10 meters, but I have never been all that
enthusiastic about that approach. At any rate, I only have a few of the
2.4-inchers on hand.
P.P.P.S. I don't know if I have correctly sized/wound them, but I wish I would
have learned about K9YC-style chokes much earlier in my ham career. Since I
have used them (past 6-8 years) the level of locally received noise on all
external and attic-mounted antennas has dropped dramatically. I have new
appreciation for the intricasies of winding, designing, and testing them, but
right now I just want someone "in the know" to help me wind something that
works reasonably well from the materials I have on hand. :)
My book, "Stealth Amateur Radio," is now available from www.stealthamateur.com
and on the Amazon Kindle (soon)
On Friday, November 6, 2020, 2:59:10 PM CST, Artek Manuals
<manuals@artekmanuals.com> wrote:
Jim
Show me the ACTUAL antenna range pattern measurement data with and
without the common mode choke on a a similar antenna, with a reasonable
SWR ( LESS THAN 1.5:1) and the feed line has been brought down
perpendicular to the plane of the antenna and I will concede you the point
Dave
NR1DX
On 11/6/2020 3:37 PM, Jim Brown wrote:
> On 11/6/2020 12:28 PM, Artek Manuals wrote:
>> The short answer is how tight you make the turns will have little
>> real world effect.
>
> That short answer is WRONG.
>
> Use the RG-8X I would probably use the #31 core over the
>> 43 . The poor mans 8 turns of coax 4-5" in diameter without ferrites
>> will probably actually work as well.
>
> Define "work." The important thing a choke should do is kill common
> mode current on the feedline that couples noise to the antenna and
> fills in nulls in the antenna's pattern. That "poor man's" solution
> won't do much for that. If "work" means it won't overheat, yes, it
> would "work."
>
>> Depending on SWR and feed line dressing (always perpendicular to the
>> plane of the beam the need for choke at all� is arguable
>
> It's arguable only if you don't understand the problem, or don't care
> about noise or the antenna's nulls.
>
> 73, Jim K9YC
> _______________________________________________
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>
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