[RFI] Old wives tail, or true?

[David Eckhardt]

I see we can attach something to email within this group.   Therefore,
please see the attachment.

My antennas are deployed in a relatively RF quiet area well outside cities
and in the county where I do not see any significant housing developments.
I overlook the Little Thompson canyon and the valley leading down to the
canyon near Lyons, Colorado (which I do not see).  While it is not as quiet
as when we moved in, its pretty good.  It has to be for my radio astronomy
hobby.  The vast majority of the RFI I experience originates from the new
appliances (2014) with their many.....many embedded SMPSs (From China, with
Love).  Again, note appliances are specifically written out of the FCC
rules and SMPSs breeze through customs with absolutely no attention paid to
RFI as FCC treats them as components.  I've tamed most of them, but there
is still a bit of RFI that gets onto my feedlines which must be dealt
with.

So, one afternoon on a whim, I made a test first with the CMC inline and
then w/o CMC on my parallel conductor transmission line to / from my
450-foot long double.  My CMCs are constructed using either 240-31
(2.4-inch OD) or 400-31 (4.0-inch OD) material and are wound in a bifilar
manner using AWG #12 Teflon insulated stranded conductors.  I do not use
coaxial cable wound on these cores due to constraints the long doublet plus
feedline places on impedances in the shack (7.000 MHz measures 3.6 - j 62
with the coaxial choke inline).  The CMC choke was placed between the
output of the homebrew L-network matching network and the input to the
parallel conductor feedline in the shack.  The results are documented in
the attachment.  Let the data speak for itself.

And I should add there are good and sound engineering reasons for this
noise getting onto the feedline, but not the subject (could be rather long
with math) of this email.

Dave - WØLEV

On Fri, Apr 9, 2021 at 3:46 AM 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*