Hi Jim,
Thanks.
I know and follow your guidelines really well, but I have to tell you that
when working in someones house that is not a hams we should not be
installing anything special if at all possible (unless it's indeed one
simple choke on the power cord and that's even pushing it). We should
first hold the company that installed or supplied the hardware responsible
for a clean solution. In this case if it's the switch mode power supply,
then Comcast can easily provide them a different power supply or a
different Cable box that uses a different power supply to see if that fixes
the problem. The homeowner is actually going to take his Comcast cable box
and power supply to Comcast on Monday and ask for some different hardware.
We also showed the homeowner how they can easily test possible solutions
using their AM radio if Comcast technicians come to their house as right
now they can't hear any AM radio stations unless they unplug their Comcast
cable box power supply. They will also be working with Mike for possible
solutions, but as I said we should try and find the correct solution if
possible versus installing our band aids all over the place in a strangers
home. We are lucky in this case that the homeowners are very open and
willing to go the extra mile to help Mike (W9RE), so if commercial
solutions do not work then Mike can indeed take the band aid approach but
again I prefer to go the commercial route solution if at all possible.
We did try a choke made per your guidelines on the power cord, and it had
no effect. I often try your choke on power cords, and sometimes they do a
fantastic job, and other times not (sometimes probably due to issues like
you mention about other cables entering and exiting the box, but sometimes
it was due to the fact that I needed to use a differential mode filter on
the power line or a combination of both).
While I'm preaching, I also think we have gotten overboard on this
reflector regarding SDR screen shots, audio recordings of noise, etc. from
people asking what their source of RFI might be. Time and time again while
out tracking down noise I have found that the only thing that matters is to
identify the property (location) generating the noise using radio direction
finding equipment (which can often be very simple home brew equipment which
most of mine is), and then track down the offending device within the
property. Too many times when I'm out hunting down noise that's bothering
another ham we waste time and take too many tangents when one thinks they
know what the source is.
Just my opinion, and a little cranky after tracking down too many noise
sources this week and it's just a hobby, and I still have a day job with
lots of worldwide travel. On the positive side I sure got a lot of steps
in on my Fitbit this week.
73,
Don (wd8dsb)
On Sun, Feb 23, 2020 at 3:42 AM Jim Brown <jim@audiosystemsgroup.com> wrote:
> On 2/23/2020 12:22 AM, Don Kirk wrote:
> > They are now going to work with Comcast and Mike to find a solution as a
> > power line choke made with a number 31 material Toroid core did not
> reduce
> > the RFI.
>
> Don (and Mike),
>
> Every cable connected to the box can be an antenna so it needs a choke.
> I'd start with the coax and power. Use the guidelines in the chasing
> noise app note below and the new HF choke cookbook, depending on the
> size of the cable you're choking and the frequency(ies) that are
> bothering you. See Fig 2 on page 2 and the associated discussion.
>
> http://k9yc.com/KillingReceiveNoise.pdf
>
> 73, Jim K9YC
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>
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