
(Now a bi-weekly program)
November 13, 2012
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RFI Detective
Overview
In this episode #43 w
e discuss the topic of finding and eliminating local sources of noise that
interfere with signal reception and trying to mitigate them. The basic process
is to first try to characterize what the noise characteristics are then to use
fairly standard troubleshooting techniques to identify the source(s) and to
describe the measures that can be taken to lessen or eliminate the noise. And
per usual, we have a great set of references for further study, and a "project"
that you can build and use in the shack or around the home to locate troublesome
interference.
73, George N2APB & Joe N2CX
Audio Recording
... (Listen
to the MP3 podcast)
Discussion
Notes:
<20:14:15> "Ray K2ULR": The K9YC paper is a classic.
<20:19:09> "George - N2APB": Which is the K9YC paper Ray?
<20:36:53> "Ray K2ULR": That's the Jim Brown paper.. Web link #1. Should be must
reading for all hams.
<20:37:32> "Joe N2CX": K9YC piece is the auudiosystrmsgroup paper
<20:39:46> "Joe N2CX": spelling doesn't count....
<20:43:22> "Ken - VA3KMD": Does leaving the cable ground connections intact but
adding a parallel wire to the power supply input ground create a ground loop?
<20:44:44> "Joe N2CX": That's why the internface box folks using internal xfmrs
make a fortune
<20:45:41> "Pete - WB2QLL": You can buy ground loop isolators at any place that
sells automotive audio, including Walmart.
<20:46:31> "Clint-ka7oei": My PTT didn't work
<20:47:02> "George - N2APB": Ahhhh, NP. Glad to have you with us tonight!
<20:52:09> "Mike WA8BXN": Is RFI radiation from DSL on ih house phone lines much
of a problem?
<20:52:40> "Howie - K3HW": I use a mechanical hand-wound clock (yes! with gears
and a main spring) in the shack to eliminate square wave clock signals which
generate harmonics.
<20:52:51> "George - N2APB": I've not heard of this happening Mike ... But it
might be.
<20:53:38> "George - N2APB": Yeah, even clocks, Howie, could indeed cause
problems if too close to the radios.
<20:58:21> "Joe N2CX": Plasma TV's are yet another source of horrendous noise!
<20:58:33> "Milt-W8NUE": Amen
<20:58:39> "Joe N2CX": ON4WW
<20:58:57> "Alan W2AEW": I've got a plasma TV in my next door neighbors -
horrible on 40 and 75m
<20:59:45> "Alan W2AEW": once tracked down a bad insulator on a utility pole
using a shortwave receiver. Verified it was on the pole by whacking it with a
baseball bat
<20:59:55> "Joe N2CX": Tell 'em they cause cancer so replace with an LED
version...
<21:02:11> "Mike WA8BXN": 40 meter fox hunt starting, 73/72
<21:02:15> "Milt-W8NUE": Alan, whacking with a bat or hammer is frowned upon.
Something is wrong with the pole and might come down when whacked!
<21:02:20> "Joe N2CX": Yet another $$$ sniffer application at: http://www.tmworld.com/design/failure-analysis/4389545/Can-a-129-spectrum-analyzer-be-any-good-
<21:02:50> "Joe N2CX": At least when the pole comes down the noise will stop!
<21:03:13> "Clint-ka7oei": MPSA18, 2N5089
<21:03:19> "Joe N2CX": 2N3565 is a good low nooise audio transistor for the
TAPIR
<21:03:41> "Ken - VA3KMD": Someone should bring back the Sniffer kit!
<21:04:29> "Milt-W8NUE": Radiated noise from power lines is best tracked at
VHF/UHF. At low frequencies the noise can not be easily located.
<21:05:05> "Clint-ka7oei": I use a telephone "sniffer" (the other end of a
"toner") for this sort of thing... It's just a JFET (hi-Z, grounded source) in
front of an LM386...
<21:08:53> "Lee KM4YY": The TPAIR kit appears to be sold out.
<21:09:04> "Lee KM4YY": Tapir'
<21:12:02> "George - N2APB": Yeah, Elektor often goes out of stock with their
kits. Perhaps they'll soon have it again - they don't too often dsicontinue
things. Or, perhaps put a WTB posting to the lists in hopes that someone wants
to part with thiers.
<21:13:18> "Clint-ka7oei": It's always good to use the "AM" mode when using a
receiver to find noise!
<21:14:01> "George - N2APB": Why?
<21:14:59> "Howie - K3HW": most noise is amplitude based
<21:15:07> "Clint-ka7oei": You beat me to it!
<21:15:39> "Howie - K3HW": sorry Clint - you have the floor!
<21:15:40> "George - N2APB": Outstanding comment Milt. For the record: Run the
Rx audio into a spectragram program to better understand the characteristic of
the noice.
<21:15:45> "Clint-ka7oei": If it's amplitude-modulated white noise, the 60/120
Hz component may be entirely missed unless on AM.
<21:15:46> "Joe N2CX": Alos the AM mode in most receivers is wider band!
<21:15:50> "Clint-ka7oei": No prob - saved me typing!
<21:18:41> "Clint-ka7oei": I solved that problem with 100 ohm resistors on the
clk/data leads - with 100pf caps on the equipment (not cable!) side of the NUE/KBD.
<21:19:19> "Clint-ka7oei": (100 ohm resistors are 100 ohms at almost any
frequency - unlike clamp-ons)
<21:20:32> "George - N2APB": Very good approach.
<21:22:56> "Howie - K3HW": Was able to key a 220 MHz FM Repeater with my HT in
the control room of a diesel submarine with all hatches closed which you would
think mimics (sp) a FARADAY Shield. My signal was being reradiated via coaxial
cables passing through watertight hull penetrations.
<21:22:57> "Ray K2ULR": That was the issue for me... FT-817, Buddipole, NUE-PSK
modem all within 10-15 feet
<21:24:09> "George - N2APB": That's amazing Howie. What power level in those
instances?
<21:24:09> "Joe N2CX": I'll bre a balun at the Buddiepole feedpoint would keep
RF off the coax shiled and lessen self-interfnerence.
<21:24:44> "Joe N2CX": That is I'll be, not I'llbre...
<21:25:09> "Milt-W8NUE": Our local power company is ususally eager to find bad
insulators. With our drought condx, fires are common.
<21:25:19> "Joe N2CX": Om an, I meant I'll bet!
<21:25:37> "Ray K2ULR": Buddipole has a series of chokes ("balun") as part of
the normal setup.
<21:26:38> "Joe N2CX": Ah, now they ahve learned their lesson. Early ones had no
chokes.
<21:27:11> "Howie - K3HW": A 2 watt 220 MHz HT. The NOSC Engineers (Naval Ocean
System Center) in San Diego surmised re-radiation via the coaxial cables through
the hull penetrations and up to my antennas... USS Dolphin SS-555, she is a
museum boat now in SD, CA.
<21:27:47> "Howie - K3HW": I was the comm officer/radioman at the time - My
Commanding Officer was a Ham too!
<21:27:57> "Milt-W8NUE": Must go. 73 guys!
<21:31:00> "Armand WA1UQO": Great show again guys! Thanks for all the effort.
BTW - Great teamspeak picture Alan! Gotta Go - 73
SESSION NOTES
....

From the very
informative and entertaining pages of ON4WW. (Content greatly reduced
here … view original web page for complete stories!)
The 'AL BUNDY' case
Shoestores. No more, please. It took me two years to solve this one. The RFI was
caused by a defective high voltage part of neon lighting at a shoestore.
This
is how the RFI sounded like. It took out the whole 80m band. A second and
longer soundclip
is available, on which the RFI is much less distinct in strength than the
interference on the first clip. That is because when the lighting was switched
on, it took a while for the 'sparks' to get completely active (and become more
dangerous in regard to fire hazard).
With special thanks to our Telecom services
for a job well done to bring this case to a good end.
The LATOYA NIGHTCLUB incident
This anomaly occurred during the cold wet winter months, with sparks clearly
visible on the roof. Had this happened during the previous hot summer, who knows
what could have happened. Another fire prevented?
Here
is how it sounded like at a distance of 1.5 km.
The faulty FREQUENCY CONTROLLED DEVICE at a big sportscomplex
Half December 2009, a terrible interference popped up on my southwest beverage
on the 160m band. Click
here
to view the video. First you will see and hear (AM mode) the Yaesu
FT-817ND radio picking up the intermittent interference sound, while a relay
clicks away in the background. After the camera zooms in on a relay; you can see
the I/O switch rocking sideways (sorry for the blurred quality, the macro
function was not enabled).
This interference sound was 2 kilometer away from my
Beverage antenna, and loud! It was audible on 1816-1832-1845 kHz-etc. On
this soundclip
you can hear how it sounded at my station, at 2 km distance!
It took 3 evenings
and a complete shutdown of the sports and cultural complex to locate this
electrical malfunction. At first we thaught the industrial relay, labelled C5 on
the picture to the left (click to enlarge) was at the origin of the RFI.
However, once this relay was disabled, the RFI continued. It seemed the
frequency controlled device that steers the large heating system of the sports
hall, was at the basis of this anomaly, and this assumption was proven correct
later on.
Notice the blue wire (relay point nr. 4) shows a shade of black, which
may indicate this wire has heated in the past. Due to the malfunction of the
frequency controlled device? Here is a
video
on which you can just see the green LED go off as the RFI stops.
Faulty STREET LAMP at ON4UN
February 2010. John ON4UN calls me for an inteference source hampering his
reception on the 160m band. It turned out to be a faulty street lamp. Here is a
video
on this type of interference. You will see the blue backlight of a Yaesu
FT-817ND radio, the dimmed street light during interference sequence (ignition),
and the disappearing of the interference once the lamp gets activated. Here is
another
video, taken inside John's shack.
You can hear the interference on the K3 radio, and at the end it drops off (when
the lamp gets activated). The radio is in AM mode..
The TUNNEL case
Late 2004, my reception towards JA on 160m was hampered by a barely noticeable
raised noise level. Just enough noise, when intermixing with the ever so weak
JA-signals, as to make it impossible to make out callsigns.
On this
soundclip
you hear me talking in Dutch, announcing the monitored frequencies on an AM
receiver. In this order, you can hear the RFI on the following frequencies: 3.5
MHz, 1.8 MHz, 168 kHz and 7 MHz. In between 168kHz and 7MHz you can hear me
cleaning my boots before re-entering the house.
The TRAIN case
Working on topband means working night shifts. And early morning shifts, just
before the sun gets up. My first years with beverage antennas, opened up a whole
new world. Not only in being able to work new ones, but in being able to detect
all kind of man/machine made noises. The first beverage-years, I often noticed
this annoying noise early in the morning. I couldn't pinpoint it, it came and
went, on different headings. I listened often to this sound (in AM mode), and
because of that, I immediately recognized the same sound while watching a train
go by in 'The TUNNEL case'... mystery solved! Here is a
soundclip of a train passing by... at 1
km distance! Think I made this recording in AM mode, on CW it sounds not as
distinct but is still pretty annoying. I can more or less follow the train on my
beverages... usually starting on south heading, going over southeast and east,
and finally disappearing on northeast.
The CONSTRUCTION CRANE case
Here is a
soundclip
of the first ever RFI-construction crane I encountered. You will understand that
it is impossible to copy any weak signal on topband with this type of heavy
interference. Distance from antenna to crane is 1.6 km.
Can it get worse? Here
is a
soundclip
of two construction cranes hampering my reception on topband simultaneously!
The
icing on the cake comes in this
soundclip:
a construction crane operational at 2 km distance and a train passing by at 1 km
distance...all at once...wonderful!
SNOW STATIC
Well, we can debate if this is RFI/EMI or not, but it sure makes a lot of noise.
You can often hear this on yagi antennas, but also beverages are prone to it.
Can be induced by snow, hail, even dry cold air. This kind of interference is
one of Murphy's favorites during the CQWW contests... here is a
soundclip.
The FLUORESCENT TUBE LAMP case
This was an easy one. In 2003 I bought a couple of fluorescent tube lamps to be
installed in my new shack. They are ignited with an electronic starter. On this
video
you can witness the result of a badly engineered fluorescent tube with
electronic starter, causing heavy RFI on 28 MHz. Distance from the 28 MHz
antenna to the lamp is 25 meter. If anyone has an easy solution for this one,
let me know pse (yes, I know I should get a conventional starter).
The Samsung PLASMA TV case
For some years I had an annoying interference that was centered smack in the
middle of the 80m (75m) SSB DX window. As I was not very active on 80m in those
days, I didn't immediately tackle the problem. November 2004, it was time to
take out the bike. I located the RFI source in a used car sales shop. The RFI
was caused by a Samsung plasma TV, model P2. It was continuously on during
daytime and late in the evenings. The RFI at 800m distance was noticeable at 200
kHz intervals. When close to the TV with a portable receiver, it was noticed
that the TV radiated non-wanted signals from LF into VHF spectrum. Waw. The RFI
on the
soundclip,
is recorded first on LSB, then AM mode, and back on LSB at a distance of 800m.
The da-di da-di case (solar panel inverter)
Although this is not a typical RFI source, it can be very annoying and is indeed
interfering when listening to weak signals on the 80m and 160m bands. A 10
second tone is followed by 7 seconds of two different alternating tones. These
signals were first heard in 2009. ON4UN, This
recording
was made at a distance of 1 km. Some people may think it is the Hyperfix signal
(heard in western Europe below 1825 kHz), it is not.
The FLUORESCENT TUBE LAMP case
This was an easy one. In 2003 I bought a couple of fluorescent tube lamps to be
installed in my new shack. They are ignited with an electronic starter. On this
video
you can witness the result of a badly engineered fluorescent tube with
electronic starter, causing heavy RFI on 28 MHz. Distance from the 28 MHz
antenna to the lamp is 25 meter. If anyone has an easy solution for this one,
let me know pse (yes, I know I should get a conventional starter).
The Samsung PLASMA TV case
For some years I had an annoying interference that was centered smack in the
middle of the 80m (75m) SSB DX window. As I was not very active on 80m in those
days, I didn't immediately tackle the problem. November 2004, it was time to
take out the bike. I located the RFI source in a used car sales shop. The RFI
was caused by a Samsung plasma TV, model P2. It was continuously on during
daytime and late in the evenings. The RFI at 800m distance was noticeable at 200
kHz intervals. When close to the TV with a portable receiver, it was noticed
that the TV radiated non-wanted signals from LF into VHF spectrum. Waw. The RFI
on the
soundclip,
is recorded first on LSB, then AM mode, and back on LSB at a distance of 800m.
Do you worry about
electromagnetic pollution? Wireless is cool, especially because
it works without wires. On the other hand, Wi-Fi, Bluetooth,
Zigbee, broadcast radio & TV transmitters, mobile phones and a
plethora of electronic gadgets and instruments with base
stations on every roof are polluting the electromagnetic
environment in which we live. Is this pollution harmful for
living organisms or not? Nobody really knows.
Does this worry you?
Do you wonder how dirty the ether that surrounds you really is?
Then the Elektor Tapir is what you need. A
tapir is a large browsing mammal, similar in shape to a pig,
with a short, prehensile snout. The Elektor Tapir is a small
electronic device, similar in shape to a cigarette lighter with
an antenna. It comes as a complete kit including two types of
electromagnetic detectors and earphones. Sturdy and easy to
build, the Elektor Tapir will sniff electro smog of almost any
frequency.
Kit of parts
available at a special low price.
The Tapir PCB is
sponsored by
Beta
Layout allowing us to sell the kit of parts at a
ridiculously low price of only £13.30 / € 14,95 / $21.50!


