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Re: [TowerTalk] Solenoid or Binocular configuration?

Subject: Re: [TowerTalk] Solenoid or Binocular configuration?
From: K8RI <>
Date: Mon, 22 Oct 2012 13:14:56 -0400
List-post: <">>
On 10/22/2012 9:16 AM, Mike wrote:
On 10/21/12 10:51 PM, K8RI wrote:
On 10/21/2012 6:09 PM, Jim Brown wrote:
On 10/20/2012 7:23 PM, K8RI wrote:
My question is about the difference between the 6 cores stacked or two
stacks side by side.

For a ferrite choke with close-spaced turns, it does not matter if he
cores are together or separated. What matters is the number of turns and
the number of cores.  The inductance increases with the square of the
number of turns, and in proportion to the number of cores. The
capacitance increases with the number of turns and with close spacing.
What you want is the lowest practical resonant frequency, and you can
use the measured data in my RFI tutorial as a guide.  So for the lowest
possible resonant frequency you want more turns and more cores, tightly

Thanks Jim,

It's pretty much what I figured. I actually super glue the cores into
a stack. Just 4 tiny dots of glue and then pressure for about a minute.
From the tutorial I figured 6 cores in a stack with about 9 or 10
turns of RG-400 although I can close space it all the way around the
inside, tack each turn in place with a dab of epoxy and let the
outside take care of itself.  That results in a coil about 3 to 4
inches longer than the stack but with the RG-400 flush against the
core on the inside and close to that on the outside. Stacks this long
start making 7 turns of the larger cable a lot of work.

If find a need to use the larger cable (run out of RG-400) I'd go to
the binocular format as I can wind a coil with 7, or possibly 8 turns
in a single plane that takes up less than half the volume of one wound
on a solenoid stack. It also makes for a nice, tight, and neat close
wound coil that will fit in a 6 X 6 X 4" or 8 X 8 X 4" PVC box under
the boom.  I think I'll have enough RG-400 to build these though.

I'd have to go back and look at the tutorial again, but IIRC 4 or 5
cores will be enough for the tri-bander and much more effective than
the original "cores over the coax" used.


Roger (K8RI)


What purpose does the box serve? Protecting the connectors?

Pretty much... On the beams they really serve as a stable mount for the chokes and on 160 are part of the feed connection.

On all the other antennas they just hang out in the elements.
( 80 M fan dipole )Haven't had any problems with center conductor migration ... yet.


Roger (K8RI)

73, Mike NF4L

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