Here is an interesting datum regarding RFI...
I have a friend that lives two miles from me, I live in the city, he
lives in the country, with a large rock hill between him and the same
city I live in...
Last night I was listening to VP8PJ on 40 CW, I could almost hear him
with my 6BTV, and 40 radials on the ground. I would pick out a 5NN now
and then.
Using his rig, over the phone, he was hearing VP8PJ at 100% in the
clear... Copyable 100% across a crappy phone line... For me, this was
the quiet time for RFI, S4 to S5. His background RFI on 40, S1...
VP8PJ was S3 at his place.
Both of us have the same rig, same antenna, same number of radials... I
need to move to the country, with a hill between me and all cities, or
get a remote receiver.
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 7:36 AM, Don Kirk wrote:
Hi Dave,
I totally agree with your statements and similar to how I use my SDR gear.
Thanks,
Don
On Sun, Feb 23, 2020 at 10:10 AM Dave Cole <dave@nk7z.net
<mailto:dave@nk7z.net>> wrote:
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@audiosystemsgroup.com <mailto: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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