Topband: K5NA Ferrite beads for RG-6

[Tom Rauch]

> Recently purchased 100 type 43 ferrite beads from Surplus
Sales of
> Nebraska, size
> .4 ID, .75 OD, 1.125 inches long. Used 8 of these units at
each end of rx
> cable coax,
> was quite surprised to see them kill off the remaining
neighborhood
> computer garbage
> and they seemed to improve the F/B on my EWEs.

Mike and all,

Just a few comments on common mode and stuff.

First, we can use single, dual, quad or billion shield cable
and the ingress through the shield on 160 and HF will be
immeasurable. Any trash we hear spills over the shield onto
the antenna, and then works its way back in. The snake
actually works on that same method. You intentionally mess
up the shield connection, and that lets outer shield current
spill over to the center. Nothing noticeable goes through
the shield. My point here is to not be caught up in the HiFi
TV marketing that quad shield corrects sloppy design or that
it is worth any extra money. If you have it, OK.....but
don't go out of your way to buy it. As an example I have
some 2500 foot long lines and they are dead for signals when
terminated, open, or shorted. That's true for single, dual,
or solid shields.

Second, any change we see in common mode noise is related to
common mode impedance ratios of the coax and the feedpoint
ground. You can have leakage in a high impedance shield
connection that allows stuff in, but in a system with good
connections and proper connector mounting all the junk you
hear gets in via the antenna.

An EWE feedpoint, like the K9AY and everything else, is
dependent on the ground connection quality. The feedline
shield common mode current "pushes" against the ground, and
if not a "solid footing" it can wiggle the ground rod up and
down with RF voltage. Since the antenna works against that
ground, any noise or unwanted signal currents on the shield
can easily get into the antenna. Of course it can also get
in if connectors do not solidly connect to the return path
for the center conductor. That's why I warned the fellow a
while back about switching shields on the feedlines, and why
when he checked he found that was actually a major problem
in his system! Improve the ground a reasonable amount first,
and then any added decoupling works better.

Finally, 43 mix is working for you but I would probably not
use it for suppression at HF. 43 mix has about half the
impedance per unit length of material along the shield as 73
material, and the impedance is largely inductive. The higher
the material Q, the lower the resistance. That means there
are more cases where adding an inductive CM choke from 43
material will increase unwanted coupling compared to lower-Q
73 materials.

I'm not saying it won't work, just that it isn't the
preferred choice for lower HF suppression. Where I would use
43 material is in higher power transmitting balun or sleeve
applications.

73 Tom