In article ,
Barett wrote:

I have found some FT140-43's.

Do you know if I stacked 3 Ferrite FT140-43's rings and wound 6 winding of
RG58cu through, what would the maximum impedance Ohms could I expect @
3.5MHz?

I did something like that a few years ago, to build a common-mode
choke for our ARES/RACES ham shack's HF feedline.

I used off-the-shelf (surplus-store) ferrite tubes - very probably a
43 mix or something close to it, based on the simple inductance
measurements I did with an MFJ analyzer. They're roughly 1 inch long,
and large enough to allow three through-the-center passes of RG-8X coax.

I glued somewhere around six of them, end-to-end, to create a long
tube, and then ran the RG-8X through... creating a long three-turn
choke. Added N connectors to the ends of the coax and stuffed the
whole thing into a chunk of PVC tube with end-caps.

The results were gratifying. When I tried a common-mode measurement -
along the braid, from one end connector to the other - the impedance
at 3.5 MHz was too high for the MFJ meter to read it... it simply said
" 1500".

A normal (differential-mode) measurement through the coax, looking
into a 50-ohm dummy load, reads 50 ohms (1:1 SWR) as closely as
matters not (i.e. within the accuracy of the MFJ meter).

--
Dave Platt AE6EO
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