One can do better than 7 turns inside FT240 forms if you use RG400 for the
winding and terminate the winding PL259's with UG175 adapters for the
RG400.
Choke made this way are near indestructible except ferrite cores blocking
hundreds of volts RF common mode. RG400 is rated 7 kW due to teflon jacket,
dielectric and fine silvered copper weave and flexible multistrand center
conductor. Requires connectors, but so does any commercial choke, and not
all of them use the high quality coax. Soldering RG400 is nice because you
can't melt it. The usual sealing procedure for choke to regular coax: tape
to cover shells and double female adapter, coax wrap over all that plus
half inch either end, tape over coax wrap, scotch liquid tape over tape.
If you do it this way, you can measure and test the thing on the bench
before you ever take it outside.
I've made those with T300A-2 powdered iron cores and a parallel HEC cap in
the center and resonated them at 1.9 or 2 MHz for a parallel tuned block
where levels to be blocked have heated and destroyed #31's (extreme
unfortunate situation).
73, Guy K2AV
*--------------------------------*
*Lowering SWR does *
* not *
* predict performance.*
*A dummy load, *
* with its perfect SWR, *
* is a worse antenna *
* than a light bulb. *
*First discern and remove *
* the loss in low band*
* antenna systems.*
*----------------------------------*
On Fri, Mar 30, 2018 at 12:09 PM, Jim Thomson <jim.thom@telus.net> wrote:
> Date: Fri, 30 Mar 2018 07:22:18 -0400
> From: "N2TK, Tony" <tony.kaz@verizon.net>
> To: <topband@contesting.com>
> Subject: Topband: 160M Balun
>
> <I shunt feed my tower for Topband. Presently using a Comtek 100 bead
> balun.
> <After reading K9YC's article on baluns it would seem that a stack of five
> #31 cores with 7 turns of coax would be a better balun.
> <Would I notice an improvement in any way by switching baluns?
> <If the answer is I would notice an improvement what about using sixteen
> <turns #12 THHN wire on #31 core as shown in K9YC's article? How many
> cores
> <would I need for 1500W?
> <Tnx for any feedback
>
> <N2TK, Tony
>
> ## Although 7 turns of 213 sized coax through 5 x type 31
> cores works good
> on 160m... aprx 5 k ohms, the choke will resonate on 3 mhz ! You
> cant get more than
> 7 turns of coax through a 2.4 inch OD / 1.4 inch ID core. The 160m
> CM choke needs
> to resonate lower in freq. It requires more cores to shift the res freq
> down. I dont
> know how many more, but I suspect 7-12 cores would do the job, and
> certainly
> be an improvement. You wont blow it up either.
>
> ## I suspect your current bead balun wont provide very much Z on
> 160m..and it
> will all be reactive.
>
> Jim VE7RF
>
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