[Skimmertalk] I'm trying to build a common mode choke for 2, 200 and 630 meters and don't know what I'm doing

[Wes Cosand]

Let's try this a third time

 I need some help.



Jack Smith, K8ZOA (SK), wrote an impressive web page some years ago
describing how he improved the performance of his active vertical antenna
using chokes at both ends of the coax.

https://web.archive.org/web/20150803213958/http://www.clifto
nlaboratories.com/vlf_signals_with_improved_setup.htm
<https://web.archive.org/web/20150803213958/http:/www.cliftonlaboratories.com/vlf_signals_with_improved_setup.htm>



 I am trying to replicate that although using a different active antenna.
But it isn't trivial to find toroids that provide much impedance at
100kHz.  It is my understanding that the most appropriate easily available
Fair-Rite mix is their type "75".



I bought 25 Fair-Rite 5975001801 toroids from Mouser.  They have an
internal diameter of only 0.54 inches so I bought some RG-174-U planning to
use about a dozen toroids at each end of the cable.  But I was surprised
how few turns I could get through a stack of toroids, especially if I wound
them in reasonably tightly.  Here is a photo of my attempt:

https://photos.app.goo.gl/zeRaPbKiDViWIvJj2


This toroid has an A of 3,025 nH.   Using the formulas in
http://ka7oei.blogspot.com/2017/11/a-semi-typical-suburban-e-field-whip.html
I calculate something like an impedance of 6900 ohms for these 25 toroids
at 100 khz.

Mouser stocks a type 75 toroid with an internal diameter of 1.4 inches with
an A of 6850.

How do I do this better?  Even putting a crimp BNC on coax is a new
experience for me and I am feeling incompetent.  When I put this assembly
on the receiver end of the coax before the coax power supply I observe very
little obvious difference in the noise level at 136 kHz in HDSDR.  Is that
expecting too much?

Am I "straining at gnats and swallowing camels"?



Wes WZ7I