This thread reminds me of one of my most challenging interference
investigations. The source was not VDSL or anything related to cable TV or
Telco Internet service but it exhibited very similar characteristics.
When first called in by an Amateur Radio Operator to investigate the
interference problem, I was at first perplexed by how I was going to find
the source.
The complainant was a well-known contesting enthusiast who was well
equipped with top flight radio gear, several tall towers, effective
antennas and a problem that started on the 160 meter band and fell off just
above the 40 meter band. Observing the interference on the complainant's
radio, I noted that the signal strength meter held fairly steady at S9 to
15 dB over 9 continuously. Signal strength was strongest at the low end and
weakest at the high end. Not surprising to me. Almost nothing about the
interference could be *heard* except for a continuous low intensity high
pitch tone that could be heard all across the spectrum affected by the
interference.
I concluded almost immediately that the source was not a power line source
but I wanted to meet this challenge. I did a "normal" power line survey and
found a few real power line sources. The discovery of the power line
sources bought me time to pursue the other primary source. Eliminating the
power line sources would also make it easier for me to locate the more
challenging primary source.
My mobile RFI hunting setup did not reliably duplicate what I saw on the
complainant's radio except for the continuous low intensity high pitched
tone. The interference just wasn't strong enough in my mobile receiver to
pop up above the noise floor very much. A 160, 80 or 40 meter directional
antenna was not practical to carry or mount on the truck. At the time I
worked this case I tried using the National RF HFDF Vector Gun Active Loop
which did work well at 40 meters. I also had a Hi-Q 4/80 mobile screwdriver
style vertical. But the interference signal seemed to be everywhere and
finding a signal level peak was extraordinarily difficult.
In the end I was forced to perform an expanding circle search which
eventually brought me to a 1 acre or so rural-ish homestead with a large
fenced pen or pasture outfitted with an electric fence that was also a
broadband transmitter creating the primary source affecting the
complainant. In all I spent about 14 man-hours (7 two hour visits over 3
months to the area which was well outside my normal territory) to locate
the actual source.
Because the source was privately owned, non-utility equipment I was unable
to pursue the matter further. Instead, I had to inform the complainant that
he was going to have to contact the owner of the source equipment himself
to work out a resolution. The complainant travels often and wasn't very
interested in confronting the owner of the source. It took nearly a year
but I believe the owner was contacted and some sort of solution was worked
out. I say, "I believe" because the complainant didn't get back to me with
updates on whatever progress he was making.
This case was challenging because there was no signature to match. The
source was weak to my search setup and had only one characteristic that
made it possible to locate. The source had an antenna that was essentially
a square loop only a few feet above ground and the affected frequencies
precluded the use of Yagi-style antennas.
In the end, patient direction finding located the source. Resolution was
dependent on an unpredictable owner. But at least the source was known.
Good luck & Good Hunting,
Frank N. Haas KB4T
Utility Interference Investigator
Florida
On Sun, Jul 16, 2017 at 9:52 AM, David Robbins <k1ttt@verizon.net> wrote:
> And complaining to AT&T about something that might be their problem and
> that
> their techs have no idea how to find or fix won't help. If you think it is
> your modem just unplug it from both the power and dsl line and see if it
> gets quieter. If there are neighbors close enough that it could be from
> them you may have to convince them to help you. if its not yours maybe
> df'ing with a small loop and portable hf radio will help find it.
>
> More about frequency bands for various versions of dsl:
> https://en.wikipedia.org/wiki/VDSL
> And uverse: http://adslm.dohrenburg.net/uverse/
>
> It looks more like uverse if it starts near 3775 as shown in the second
> link.
>
> David Robbins K1TTT
> e-mail: mailto:k1ttt@arrl.net
> web: http://wiki.k1ttt.net
> AR-Cluster node: 145.69MHz or telnet://k1ttt.net:7373
>
>
>
> -----Original Message-----
> From: RFI [mailto:rfi-bounces@contesting.com] On Behalf Of Rob Atkinson
> Sent: Sunday, July 16, 2017 12:09
> To: rfi
> Subject: [RFI] white noise starting at 3780 and up
>
> Howdy,
>
> I've been tolerating something here that is a nuisance for the past few
> years: Tuning up through 75 meters, at around 3780 or 3790, the band noise
> suddenly goes up 20 dB and stays there all the way up to over 5 MHz. It's
> just white noise, like data. Does anyone else have
> this? I suspect it is AT&T VDSL but I want to find out if there are
> other possible causes. It's puzzling that only that one frequency
> range has the noise since Uverse or VDSL whatever it is, uses a number of
> other "bands" for data uplink and downlink. I have done nothing partly,
> because the whole scenario of calling AT&T and getting to a human who knows
> what I'm talking about will probably take hours and be a frustrating
> nightmare but every time I tune down the band and have the noise floor
> suddenly drop I get ticked off.
>
> I guess I'm hoping someone else has had this problem and dealt with it
> and can give me some pointers. If it is indeed an AT&T problem maybe
> there's a secret phone number to get me right to a technician.
>
> tnx and 73
>
> Rob
> K5UJ
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>
--
Frank N. Haas KB4T
Utility Interference Investigator
Florida
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