[TowerTalk] Fabricated common mode chokes and their impedances

[K8RI on TT]

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 mode
> chokes for their stations.
>
> I built and measured 18 of this type of choke during the past week. There is
> 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.

73

Roger (K8RI)