Topband: Toroidal common mode choke

[Guy Olinger K2AV]

What I like about some of the #31 stuff is that I can get those large
clamp-ons, wind a particular kind of conductor through it, and then put it
up on my analyzer and "tune" that nice resistance hump.  This has allowed
me to some very effective *targeted* interceptions, which both stopped some
TV radiated stuff dead in it's tracks and kept RFI out of the entertainment
device.  #31 is really good stuff for low bands.

Replace existing #43 stuff that's working?  No way.  Do any NEW #43 stuff
for low bands?  No to that also.

The one place where getting the CM exactly right is coming from low level
RX antennas.  Seems some people shoot the cockroach with a 70mm cannon,
where others do nothing at all.

If we were in the business of measuring signal to noise as we were putting
these things in, we would know the CM noise we DID have, and also know when
we had pushed it well under incoming noise and stop at that point.

In these discussions what I see developing is some communal sense of where
that least best point is.  Good for that.

I do have a box of #31 FT240's which slowly but surely are getting used, by
myself and folks I help.  What I really like about them is how often just
one of the #31 devices does the trick.

On Tue, Nov 20, 2012 at 8:42 AM, Tom W8JI <w8ji at w8ji.com> wrote:

> On paper I agree but what about real world? Topbanders seemed to do quite
>> well with the old 43 mix and the resultant lower impedance.
>>
>> How much is good enough?
>>
>
> That's a good point.
>
> It seems we tend to go to extremes of black and white and abandon common
> sense or reasoning in everything we do these days. That pattern has crept
> into some very simple things, perhaps so one answer fits all and no one
> ever says "it depends".
>
>
>  I havent changed any of the 43 material in the house since they removed
>> the noise from each consumer device; some have been in place for over 30
>> years going back to the prior QTH. As new stuff is added I use 31 mix,
>> seems to work the same.
>>
>
> I've never been a big proponent of peppering a system with beads, because
> often a common-mode series impedance by itself is the least efficient way
> to do mitigation. It takes a terrible CM signal levels to cause problems,
> if connectors are good and the antenna is a reasonable distance away. If
> the antenna isn't a reasonable distance away, then correcting the source is
> often better.
>
> It's really a big soup of things, and I think some of this has gone beyond
> sensible solutions. I lived years without problems without any ferrite
> cores, BUT I grounded feeders sensibly and looked at the system. It all
> about ratios and changes in CM impedances.
>
> Once something fixes something, it all seems the same. After all, fixed is
> fixed.
>
> Correct me if I am wrong, but it seems we think noise all comes from
> common mode and if we add increased suppression things get better and
> better with nearly no limits. We become almost anorexic with suppression.
> What really happens is once antenna noise dominates, which can even happen
> without any suppression at all in many systems, all the rest is a wasted
> effort. In other systems once the feedline has reasonable suppression,
> direct radiation takes over. We can add a billion beads to the feeder and
> nothing changes.
>
> There should be more focus on telling people how to find problems, and
> less on treating every system the same.
>
> I was visiting a friend and he told me stories about building massive bead
> strings a few feet long on Yagi antennas!! Someone should stop the bead
> madness enveloping us, and get us back to rational thought.
>
> 73 Tom
> ______________________________**_________________
> Topband reflector - topband at contesting.com
>