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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