[RFI] 160 meter noise at W9RE tracked down to neighbors Comcast Cable Box / Power Supply

[Dave Cole]

Hi Don,

I tend to agree with you somewhat on the SDR issue-- SDR is great at 
defining what noise type one is having, what your general RFI 
environment looks like, and in general, what is happening around you in 
the RFI world.

However it will not in most cases, let you say, "Oh, look there is a GE 
oven clock on a GE model 12345".

SDR will let you say, I have some very broadband RFI, or I have some 
narrow band RFI, the the RFI I have is on a schedule,etc., and that type 
of data, tends to point to these types of devices, etc.

SDR helps define the tools needed to hunt, and some indications as to 
what you might be looking for...  SDR will help you define when to hunt, 
if your source is on a schedule, etc...

So in the way of "lets ID the source to the part number", sort of way, I 
agree, we are slipping a bit into that mode using a SDRs.

I use my SDR to point me in a general direction for tools, hunting 
methods, and times...

I also use it to quantify what my RFI is prior to a fix, and then check 
after the fix.  SDR has its place, but it is not defining an RFI source 
to the item part number.

Every 6 months to a year, I do a full spectrum record of my RFI across a 
24 hour period using HDSDR, then save that data.  That helps me see what 
is happening around me over time...  There is a place for SDR in RFI 
hunting-- as a guide to what further steps to take, and in defining what 
is happening around you over long time frames...

73, and thanks,
Dave (NK7Z)
https://www.nk7z.net
ARRL Volunteer Examiner
ARRL Technical Specialist
ARRL Asst. Director, NW Division, Technical Resources

On 2/23/20 5:12 AM, Don Kirk wrote:
> 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 at 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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