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Re: [TowerTalk] Terminate braid at top of tower...or

To: "Kelly Taylor" <ve4xt@mymts.net>, "Stan Stockton" <wa5rtg@gmail.com>
Subject: Re: [TowerTalk] Terminate braid at top of tower...or
From: "Jim Thomson" <jim.thom@telus.net>
Date: Tue, 4 Nov 2014 10:41:36 -0800
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>
###  W1JR and Chuck counselman figured out winding coax on ferrite cores....
a loooong time ago.  Nobody was doing proper Z measurements back then.
Jr used type 61....and Chuck used type 43. On wire dipoles, the coax /ferrite chokes could be better optimized for that one band, or 2 bands. You could also
use 2 of em.. a few feet apart, for more CM Z..or even stagger tune them for
wide band coverage.

## Nobody is knocking Jim and steves excellent work..but the design has to be practical for the application at hand...and there are a trillion yagis out there. I don’t like separating coax ends into braid + center conductor...then trying to water proof the Y /crotch. IMO, it would be easier if the yagi makers installed water proof female coax connectors on the feed points. Then just install the usual male connector on the end of your main coax..where it
exits the choke balun..or beads.  Ditto with wire dipole ants.

## be careful using designs where 8-14 turns of coax are used on a core. You can easily get parasitic arcing between the braids of adjacent turns. Use more cores..and less turns..like 4-6 max. I have seen that happen with both RG-400..and also RG-303. Both are teflon coax..and inexpensive. I would not mess with RG-58. Get any of the turns anywhere near
metal..and all bets are off.

Jim  VE7RF



From: Kelly Taylor
Sent: Tuesday, November 04, 2014 6:10 AM
Cc: <towertalk@contesting.com>
Subject: Re: [TowerTalk] Terminate braid at top of tower...or

I've read Jim's choke cookbook, and I won't pretend to say I understand all
(maybe even any) of the math involved.

However, I can't escape the feeling you both reading too much into his
design of an RG-213 choke on cores?

He does also talk about compact bifilar windings on fewer cores, and
quadrifilar windings on dual core stacks, although not in as great a detail
on construction as the coax loops.

I agree, the coax loops might be a challenge for mounting to a yagi: Does
anyone see any instance where his cookbook shows those chokes on a yagi?
IIRC, most of his coax chokes are on wire antennas.

What I took away from Jim's RG-213 choke is this: for the right application,
for about $25 in cores and some coax from your collection, you can produce a
choke comparable to or superior than some of the commercial products costing
anywhere from $60 to $200.

At the base of a vertical, as an isolator for an end-fed coaxial dipole
(where the isolator-to-feedpoint part of the shield is one half of the
dipole) or as the feedpoint of an inverted vee (use a non-conductive sidearm
as an antenna support and mount the choke on the sidearm), are they not
useful and inexpensive? On an end-supported dipole with the feedpoint
suspended in the air, is the coax choke significantly heavier than an Array
Solutions box?

In the spirit of ham-radio frugality, is that not worth something?

Methinks there's a bit of a straw-man argument here in criticizing Jim for
something he never said.

73, kelly
ve4xt

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