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Re: [TowerTalk] Fabricated common mode chokes and their impedances

To: "'K8RI on TT'" <>, <>
Subject: Re: [TowerTalk] Fabricated common mode chokes and their impedances
From: "Tod - ID" <>
Date: Mon, 29 Aug 2011 08:01:08 -0600
List-post: <">>
How high is the SWR on your feed line Roger? If I was using a feed line that
had 3:1 or higher I expect I would want to use something other than RG58,
RG59 or RG8X. Davis BuryFlex certainly will do the job but I think Teflon
dielectric coax will work too. Have you tried RG400U as the coax for the
chokes? That is what I use here in Idaho,

I have plans to run measurements on 5 and 6 cores but maybe not until I
return to Idaho in late September. The experiments that I have run clearly
show that an extra turn produces more 'bang' than an extra core. That agrees
with the theory of course.

73, Tod, K0TO

-----Original Message-----
[] On Behalf Of K8RI on TT
Sent: Monday, August 29, 2011 3:11 AM
Subject: Re: [TowerTalk] Fabricated common mode chokes and their impedances

On 8/28/2011 6:51 PM, Tod wrote:
> This probably has a limited audience but I do know that there are some
> readers on this list interested in fabrication of high impedance common
> chokes for their stations.
> I built and measured 18 of this type of choke during the past week. There
> a write-up on my web site which shows how they were fabricated, how they
> were measured and the measurement results. I used Fair-Rite 2.4 inch
> diameter type 31 toroidal cores and small diameter [RG 59 size} coax. I
> measured the magnitude of the impedance for each of the chokes on the 160,
> 80, 40, 20, 15 and 10 meter bands. There are also attenuation values for
> each choke [specific to the 50 ohm measurement circuit]. The results are
> shown as a series of graphs for two cores, three cores and four cores with
> 3, 4, 5, 6, 7 and 8 turns on the core bundle.

I use 5 and 6 turns of Davis BuryFlex on 5 and 6 cores of the same 
type.  8X and 59 will not handle the high SWR when operating the entire 
75 meter band at the legal limit.


Roger (K8RI)


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