
Amateur Radio Sleuthing Pins Down Source of Strange RF Interference - xoa
http://www.arrl.org/news/view/amateur-radio-sleuthing-pins-down-source-of-strange-rf-interference
======
xoa
If you scroll down a bit, you'll see that sure enough this involved a
switched-mode power supply, /probably some very cheap no-name/ [nope, missed
that they included pictures of it]. Even though they're supposed to be at
least minimally regulated under Title 47 part 15(B), in practice they're often
a plague upon RF and as the article states sometimes the FCC has trouble
mustering the energy for small spot trouble. While I feel more generous
towards the FCC then some of the commentary I've seen on this, in that I don't
think they've been remotely allocated the resources they should have to deal
with this kind of small hotspot popping up since historically it was less an
emergency matter, it's an issue (and a bit more surprising when it's a request
from law enforcement, even if local).

I think it's a good reminder though that while modern wireless links represent
a lot of fantastic engineering and are very valuable they can also be pretty
fragile, and it's important to have a physical (be it digital or mechanical)
fallback for critical tasks like authentication (in this case to access or
startup a vehicle). There are situations where being surprisingly unable to
operate ones vehicle (or access a building or whatever) could be quite
serious, and the IoT ecosystem needs to give surprise interference some
consideration as well. These sorts of incidents should also make society think
about failure modes when it comes to interference, be it accidental or
intentional. Law enforcement in particular should consider it from two sides,
both in terms of emergency planning for if there was a major case (during an
emergency or not), and as a strong note of caution vs some of the noises that
have been made about LEOs themselves purposefully doing jamming during
"periods of unrest" or the like. In an age of ever proliferating wireless
devices, beware unintended consequences.

[Edit]: Thanks to Animats below for pointing out that it's UL approved Ventex,
it's not in the article text but a photo is included at the bottom. So I guess
that underlines SMPS quality control issues can be tough even with more
attention paid, and shouldn't be taken for granted in planning even with part
control. Though this also seems like it should make it something the FCC
should give more attention in terms of confirming that this was a lemon and
not an indicator of some more widespread problem. It should be easier for them
to do that with a US-based operation.

~~~
Florin_Andrei
As someone who has designed and built switching power supplies, the article
brought back funny memories.

It's so easy to make an SPS that is essentially a disaster for all RF spectrum
around it. In fact, some of my early SPSs, I could "detect" they were on
because the noise coming out of a radio receiver nearby would change when I
turned the supply on.

OTOH, it's pretty easy to take measures that ensure the RF is kept under
control. Shielding is important, but first make sure your circuit doesn't make
excessive amounts of RF to begin with.

~~~
lutusp
> As someone who has designed and built switching power supplies, the article
> brought back funny memories.

Myself also. I designed switching power supplies for the Space Shuttle, some
of which were meant to power fluorescent lights. NASA wanted dimmable
fluorescent lights in the crew quarters, but they also wanted no EMI. Well,
they got both -- I figured out a way to dim the fluorescents using a magnetic
amplifier instead of the semiconductor switching methods that were common at
the time, and (as I intended) the magnetic amplifier created no interference
at all.

The details:
[http://arachnoid.com/PDF_archive/IES_october_1976.pdf](http://arachnoid.com/PDF_archive/IES_october_1976.pdf)

~~~
Gibbon1
That's amusing. I have a bombarder for a neon shop, it uses a magnetic
amplifiers to control the current. Thing weighs about 75lbs.

------
ekianjo
I find the conclusion a bit strange:

> The troublesome transformer was not replaced, but the building owner agreed
> to turn off the sign should problems arise.

I thought they said it was a potential danger if folks cannot use their phones
nearby, but then they dont take action to take down the sign. Are they waiting
for an emergency to happen first?

~~~
jeff_vader
It was found by a radio amateur, not FCC. So the only way to deal with this is
asking nicely and expecting cooperation.

~~~
PhasmaFelis
Found by a radio amateur at the request of local police! It's a clear public
safety issue, and clearly illegal. Why didn't the police tell him to turn it
off?

~~~
chillingeffect
Not to be overly cynical but "safety" is the rationalization. They really were
hoping to catch a car thief.

~~~
PhasmaFelis
They were expecting someone with an illegal jammer, maybe. I'm not sure where
you get "car thief" out of that. 911 calls are the reason jammers are illegal,
and it was also causing major inconvenience to some drivers with electronic
key fobs--either one should be a sufficient nuisance for law enforcement to
step in.

------
vvanders
Kinda surprised the FCC/Wireless providers didn't help. Usually when there's
911 connectivity issues they take it pretty seriously.

I remember a story a while back where someone was driving around with a
cellphone jammer since he was sick of people talking and driving. They caught
him by noticing his commute pattern as connectivity dropped along the freeway
he took each day.

[edit] Also another great example of hams helping the local community. Quite a
few clubs run communication for remote events(think large bike races/etc)
often free of charge and it always great to see technology used in this way.

~~~
mmagin
Funding for the enforcement branch of the FCC has been seriously cut in recent
years.

~~~
vvanders
Ah, that would help explain it.

Shame though, the number of wireless things is only going to grow. The amount
of stuff I pick up just driving around on 2m is pretty incredible.

~~~
wyager
I just drove 3000 miles listening on 144.39, 146.46, 146.52, 446.0, and all CB
frequencies. There's a fair amount of garbage on the calling frequencies, but
CB is really bad. I get horrible noise driving past power lines especially.

Also, I was surprised with the level of activity on APRS. Lots of tracking and
weather data.

------
okket
TL;DR

"The interference source turned out to be a recently replaced neon sign
switching-mode power supply, which was generating a substantial signal within
the on-street parking area just across the sidewalk, between 8 and 40 feet
from the sign."

------
TazeTSchnitzel
Odd the FCC didn't intervene. Here in the UK, Ofcom (our FCC equivalent) has
done so in some similar situations ([http://consumers.ofcom.org.uk/news/ghost-
busting-in-winderme...](http://consumers.ofcom.org.uk/news/ghost-busting-in-
windermere/), [http://www.bbc.co.uk/news/uk-england-
hampshire-15306994](http://www.bbc.co.uk/news/uk-england-hampshire-15306994)).

Are key fobs are the canary in the coal mine of RF interference? There's a lot
of stories of RF interference stopping them working in different places.
Apparently, Ofcom dealt with 140 cases in 2010 alone:
[http://www.dailymail.co.uk/news/article-2057036/Trapped-
driv...](http://www.dailymail.co.uk/news/article-2057036/Trapped-drive-TV-How-
set-boxes-interfering-car-key-fobs.html)

~~~
cnvogel
> Are key fobs are the canary in the coal mine of RF interference?

If key fobs use receivers similar to the popular and dirt cheap "433 MHz RF
Modules (ideal for Arduino)..." sold on eBay for <1$/piece: these are very,
very crude and not selective to a particular frequency at all.

So, yes, they will stop working long before anything else (built a little more
sophisticated) starts to show problems. Typically they are designed to be used
in close proximity to your car, even if some people got used to operate it at
considerable distance.

------
devy
So the neon light switching power supply's label with serial number and
manufacturer were pictured.[1] And it was UL certified but with no FCC label.
Will the manufacturer get a fine if someone files a complain? I am curious.

[1]:
[http://www.arrl.org/images/view/News/Evanston%20RFI-2.jpg](http://www.arrl.org/images/view/News/Evanston%20RFI-2.jpg)

~~~
Animats
Power supplies don't require FCC approval, just a declaration of conformity.

If a neon sign is generating RF over multiple bands, it may be the neon tube
itself. If the tube has a loose connection, there's some arcing outside the
tube, which generates broadband RF hash. Well-known problem for bands that
play small venues.

------
devy
There are tons of cheap electronics (including but not limited to switching
power supplies) that are not properly EMI shielded or even not shielded at
all. It would be great to have a portable device that can detect and locate
the EMI/RFIs. (Perhaps there are already some on kickstarter?)

~~~
leetbulb
The article states that they used "a Radar Engineers 240A Noise Signature
Receiver and UHF Yagi antenna to survey the affected block."

Looks like a somewhat portable device (MODEL 243):
[http://www.radarengineers.com/rfitvi.htm](http://www.radarengineers.com/rfitvi.htm)
Although it's probably going to cost you $5-10k USD.

Pretty easy to hook up a RTL-SDR ($10) to a cheap Android tablet loaded with
SDR Touch for simple surveying.

~~~
tzs
I tried to get a price check by dropping "Radar Engineers 240A Noise Signature
Receiver" into Google's shopping search, and for some reason all it gave me
was one result: a "My Little Pony Friendship is Magic Guardians of Harmony Fan
Series Figure - Princess Celestia" from Toys'R'Us.

Google is very weird sometimes.

Note: I have never watched "My Little Pony", collected anything related,
visited any My Little Pony fan sites, read any My Little Pony fan fiction (not
even accidentally, via crossovers from fandoms whose fiction I do read), or
done anything else to show any interest whatsoever in My Little Pony. Google
has a ton of information about me with regards to things I might actually buy,
so why the heck did they pick My Little Pony? (Heck, I'm pretty sure they have
figure out that I have a ham license...surely they have something more
relevant for me than My Little Pony).

~~~
KMag
Back when I worked at Google on the indexing system, the guy who sat next to
me introduced [http://www.nextthing.org/archives/2006/10/26/rolling-
garfiel...](http://www.nextthing.org/archives/2006/10/26/rolling-garfield-
ninja-turtles) . In his defense, it was someone else's code that he started
using more broadly, and there was a latent bug in the third person's code that
didn't special-case a sentinel value used for one of the similarity metrics.
So, he added some analysis, and all of a sudden Google thought all of the
pages that didn't have this similarity metric calculated were all extremely
similar. Our manager bought him a stuffed Garfield as a "prize" for breaking
Google.

------
basicplus2
These sorts of issues were found and solved quickly when everyone was
listening mostly to AM radio as everyone was effected.

~~~
kawfey
The article mentions key-fobs and cell phones were affected.

~~~
kazinator
But you don't hear a problem in those technologies the way you do in AM radio.
They just appear not to be working.

Your key-fob isn't opening a door. What's wrong? Dead battery? Door components
not working?

AM radio: "I hear obvious noise in the broadcast no matter which way I turn
the dial, and so does everyone else in their radio when they are in this
vicinity."

------
nickhalfasleep
The general quality of Neon and Fluorescent drivers will continue to nosedive
as both are replaced by more efficient technologies. Currently the factories
are being run out to wring the last bit of profit from these technologies as
they are replaced by LED's and their switched mode DC supplies of lower
voltage and frequency.

------
mrestko
I live right by here and had actually noticed an odd sign in the window of
that shop referencing some problem with car key fobs and that "the police are
aware". Maybe I'll stop by and take a picture tomorrow if I have time.

