[RFI] Old wives tail, or true?

[David Eckhardt]

The input of the L-Network matching network is common mode.  The output of
the matching network is common mode.  The common mode choke belongs at the
matching network output which is common mode and terminates to the feedline
which is differential mode.  I at one time used to use a completely DM
matching network.  But when I discovered the associated losses with the
components I had on hand (I needed two roller inductors) I went with the CM
matching network with the CMC placed between the matching network and the
feedline.   Everything between the matching network and the transceiver,
through the amp, is in CM coax.  Distinguish between the fine points
between CM (common mode) and DM (differential mode) and it will become
clear.

Dave - WØLEV

On Fri, Apr 9, 2021 at 8:15 PM Larry K4AB <larry.k4ab at gmail.com> wrote:

> Hello Tim and all,
>
> What's the reasoning behind placing the choke at the amp output
> as opposed right at the transceiver?
>
> 73,
> Larry K4AB
>
> On Thu, Apr 8, 2021 at 10:45 PM Tim Duffy <k3lr at k3lr.com> wrote:
>
> > Hello Alex,
> >
> > I can tell you that this test opened my eyes to how noise is propagated
> to
> > our radio receivers. Like K9YC, W1HIS and many others I have embraced
> these
> > findings. There is a reason the noise floor here at K3LR is below S0 on
> all
> > bands. This is science - nothing more.
> >
> > I have significant common mode impedance chokes at every antenna
> feedpoint
> > and at the connection to each amplifier (11) - so end to end on the
> > feedlines. The results speak for themselves.
> >
> > This is not a wives tale. Do your own research and report your results.
> >
> > 73
> > Tim K3LR
> > -----Original Message-----
> > From: RFI [mailto:rfi-bounces+k3lr=k3lr.com at contesting.com] On Behalf Of
> > alex at kr1st.com
> > Sent: Thursday, April 8, 2021 3:21 PM
> > To: Alan Higbie
> > Cc: Rfi List
> > Subject: Re: [RFI] Old wives tail, or true?
> >
> > Let me challenge that test because I'm not convinced that the test is
> > valid.
> >
> > I watched that video and it only shows the signals before and after the
> > choke has been applied, on the outside of the coax. The conclusion is
> > then drawn that all those signals make it into the receiver and causes
> > noise. Can someone explain why that would be a valid conclusion?
> > Shouldn't he be showing that those signals are indeed making it into the
> > receiver and then showing that the application of the choke indeed make
> > these signals disappear?
> >
> > I mean, I can make such measurements on any cable attached to a receiver
> > and would probably be horrified by what I would see, but that doesn't
> > mean that those signals actually make it into the receiver and cause
> > noise.
> >
> > Like someone else wrote, the best test is probably to apply the choke
> > and if it doesn't make a difference, ask for a refund from DXE. :)
> >
> > This inquiring mind would like to know.
> >
> > 73,
> > --Alex KR1ST
> >
> > On 2021-04-08 10:35, Alan Higbie wrote:
> > > In 2019 K3LR presented such a test at the Dayton Contest University.
> > >
> > > Tim describes it @ 15:30 into the presentation.
> > > Here is the YouTube link:  https://www.youtube.com/watch?v=wd5B5qPHI_U
> > >
> > > The relevant slides are at pages 41050 of his Power Point presentation.
> > > CTU 2019 14-K3LR-Contest-Station-Optimization-PLUSROTATOR.pdf
> > >
> > > 73, Alan K0AV
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-- 
*Dave - WØLEV*
*Just Let Darwin Work*