Interference in FM radio reception.

The Russians have resurrected a souped-up version of The Russian Woodpecker (Wikipedia that)! (AKA "Steelyard")

TRW was sited very close (~10km) to the nuclear power station at Pripyat, near Chernobyl.

Now the whole area is overgrown with trees, but the antenna array still stands.

And interestingly, as a westerner, I had assumed it was way north of where I am, but actually, Pripyat/Steelyard are on almost exactly the same latitude as my hometown in Kent (south-east England)!

I heard TRW on the radio when I was a kid. There was a documentary on TV about it at the time.

As for your FM problem, sorry, to be honest, I don't know. But if you find out, let us know here; I'd be interested to read what it was.

Martin

What you are describing, sounds somewhat to me as if it may be what amateur-radio operators refer to as "doubling" - the result of two signals of somewhat similar strength, on the same or near-by FM frequencies at the same time. On ham 2-meter transmissions it often has a characteristic "growling" sound. If one of the two signals is significantly stronger than the other, you may hear the music or voice from that signal, but in many cases neither transmission can be heard clearly.

If I had to guess, I'd guess that there's somebody in your neighborhood operating some sort of local-area FM transmitter. This might be:

- A "broadcast your CD player music throughout the house" device, or

- a "feed music from your CD player or iPod, through FM, into your car radio which doesn't have a direct input" device, or

- a full-fledged "pirate radio" station, or

- a legitimately-licensed "micropower" FM station (there are a few although it's not at all easy to get a license), or

- some sort of malfunctioning device, in or near your house, which is oscillating out of control and generating spurious frequency carriers. Fluorescent light ballasts, electronic heaters, defective house wiring, and computer-network gear can all do this. In all of these cases (except possibly the licensed micropower station) the offending transmission ought to be shut down, as (1) it's interfering, (2) on a frequency it shouldn't be on, (3) without a license.

It's also possible that your radios are being interfered with, by a perfectly legal (but high-powered) transmission from a nearby source... police or fire radio transmitter, ham radio, etc. Cases like this are usually the result of something called "fundamental overload" or "strong signal overload", and they are usually *not* the legal fault or responsibility of whoever is transmitting. They are (the FCC declares) the result of poor design of the receiving radio (e.g. yours) - it's not adequately shielded or filtered - and it'd be your responsibility to fix your radio. However, from the fact that you're hearing the problem only on certain frequencies, while others higher on the band are not affected, I don't think that this is the case in your situation. The fact that you're hearing it on multiple radios, gives you a pretty good assurance that it's not just a single malfunctioning radio. Are all of these radios powered from the AC mains, or are all of them battery radios, or have you heard it on some of each type?

As to locating the source... well, you're probably in for an exercise in radio direction finding! There are quite a variety of ways to trace down the location of a transmission... some require lots of equipment, some require as little as a small battery-powered portable radio and a Pringles can covered in aluminum foil (the "body fade") method.

A practical suggestion: see if you can locate one or more amateur radio clubs in your area. Within the ham community, there are a fair number of hams who enjoy "foxhunting" (radio-direction-finding contests, looking for hidden transmitters), and others who have a very specific interest in hunting for RF interferences sources and for illegal transmitters (some of the ARRL "official observer" volunteers have teams who do this). You may be able to locate some folks who would be willing to come out, with some of their direction-finding equipment, and help you locate the source of the interfering transmission.

--
Dave Platt                                    AE6EO
Friends of Jade Warrior home page:  http://www.radagast.org/jade-warrior
  I do _not_ wish to receive unsolicited commercial email, and I will
     boycott any company which has the gall to send me such ads!

"micky"

** You will need to get a portable FM radio and walk about with it to find where the source is.

Anecdotes:

1. Once had spike noise interference visible on the scope on my workbench - it began in the early evening and was at a very steady rate of once in 6 seconds. On a portable AM radio, the clicking noise was very clear. I tracked it down to a small, flashing, red neon sign in the window of a pharmacy 60 metres away.

1. Had interference on TV at about the same time, visible only on VHF channel 2 ( 63 to 70 MHz) - the colour would drop out regularly ( every 5 -

10 seconds ) and noise bands appeared. The problem was only there during the day on work days.

Turned out to be a RF plastic welding machine on 27.12 MHz in a factory 200 metres away. The particular TV was known to be vulnerable to CB radio when tuned to channel 2.

1. High frequency RF suddenly appeared on my scope one day while doing testing at full sensitivity ( 5mV /div). It disappeared after 15 minutes but then returned the next day. Turing up the time base speed showed it to be a steady signal on 29 to 30MHz.

Switched on my radio scanner and soon found that my upstairs neighbours had bought themselves a cordless telephone transmitting both ends on the conversation on 30.15 MHz.

... Phil

Cell towers around here Akron ohio rent tower space to different radio or RF links they put their dish or arrays on the towers that have been alot of RFI problems just thinking that maybe its the cause of the interference problems

(...)

Good description but not enough to identify the culprit. It doesn't sound like a heterodyne and there's no indication of any additional voice or music modulation making intermod an unlikely cause. If you could record an MP3 audio clip and post it somewhere, it would be a big help.

FM noise is fairly uncommon. FM was originally designed to ignore amplitude modulated noise, which it does quite well. However, with the introduction of HDFM, the digital modulation scheme included AM components. The result is the sensitivity to AM interference has increased. The noise description does not sound familiar so this is unlikely. However, I'm curious if the unspecified maker and model receiver is and HDFM receiver and were you possibly listening to HD1 or HD2.

Also, try a different FM receiver. If both radios receive the same interference, then its probably being radiated over the air or conducted on the power lines. However, if only one radio hears the interference on the same channel, then it's possible that there's something wrong with the receiver or the noise is being generated in the radio.

Also, your description sound vaguely like RFI from a plasma TV. The level, modulation characteristics, and frequency will vary with what is on the screen. The timing pattern you describe sounds roughly like a TV being turned on and off at random times. Do the times when it's on coincide with prime time TV?

--
Jeff Liebermann     jeffl@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann     AE6KS    831-336-2558

d

Portable FM radio, listen for the original noise, then walk around the neighborhood.

First I'm going to find my MP3 player, which has an FM radio, and try to circle in on the source of the noise. I didn't think the problem could be so far away, so it's good that I'm looking farther now. .

There are two big ham radio clubs around here, and smaller ones in adjacent counties. I go to their hamfests all the time. A few of them even know me. The problem now is that I haven't kept a log of when the interference occurs, so even if they're willing, I can't tell them when to come over. I'll keep the log, and I'll call them anyhow. Maybe one who likes foxhunting lives 5 minutes away, etc.

I plan to get back to you with more details when I know them, but it may take a while.

BTW, the two stations I mentioned are HD, so Jeff, maybe that's why they get the noise. So is 88.1, which is very close to 88.5 of course, but 88.1 is a local station, not 45 miles away, so maybe its signal is too strong for this interference to interfere????

Thaks for all the good advice.

P.S. There are also one or two buses that park 100 to 150 yards from my house. Maybe they have some fancy new electronics. They have an erratic schedule themselves, in that I thought there was never more than one and it only parked unitl i's next route began. Maybe 10 minutes, but I've been paying attention and it's more complicated. Al;so I live in the suburbs and didn't think they ran all night, but next time the noise starts in the night I'll force myself to the window to look. (Obviously I'm awake, but I don't like sitting up.)

I've no idea if it would work but can you make a portable FM receiver directional by placing in a metal tube? Perhaps with a metal plate under a shoe with a grounding wire. Would have to be speaker output , so an earpiece did not fed RF down

Not really. The tube would need to be about 1/2 wavelength long (about 1.5 meters) and would totally block the signal. If you run a

1/4 wave lengthwise slit down the length of the tube, you would be able to hear something (at reduced sensitivity). However, it wouldn't be very directional. I've built rotating tube type direction finders using this principle, but at 2.4Ghz, where the size of the antenna is more practical.

You can stop the earpiece from becoming an antenna with a simple ferrite bead at the EP jack.

Much of what you suggest has already been done by hams for transmitter hunts.

There's quite a bit of existing equipment available that will work. Something cheap and crude are the various "homer" type direction finders. Also known as TDOA (time difference of arrival).

etc..

AN/SRD-21 homer type direction finder manual (4.5MB)

Much of the technology use for the 2meter (145Mhz) ham band is directly applicable to the 88-108 band if scaled. Unfortunately, all the problems and headaches are also applicable (interference from other stations, reflections, insufficient directionality, antenna side lobes, etc).

Direction finding on the FM broadcast band is problematic because of the potential for interference from adjacent channel stations. The FM receiver IF bandwidth usually slops into the adjacent channels. In the US, we have 200KHz channels, with allocations every alternate channel. This reduces the problem, but doesn't eliminate it. In EU, it's on 100KHz channels, possibly with alternate channel allocations.

However, methinks all this is overkill for finding a noise source. The first thing I would do is turn off the power to the house, except for the FM receiver. Many noise sources are conducted (through the power lines) rather than radiated (over the air). If the noise goes away, it's coming from something in the house. From there, it's just a matter of turning off breakers until the location is isolated. Then, turn off individual pieces of equipment. I've found an amazing assortment of noise sources this way. If killing the power doesn't find it, ask the neighbors to do the same (while carrying a portable FM receiver). You'll be amazed at how many consumer devices generate disgusting levels of RFI/EMI. From the description, the 10 sec to 1 hr duration is an important clue. That points to a thermostat, air flow, or water demand operated device. It might also be an electric heater. Killing the house power should be able to isolate it.

--
Jeff Liebermann     jeffl@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann     AE6KS    831-336-2558

One thing that strikes me about this is the random (erratic?) nature of this interference, varying both in time and duration. To me, that rules out many devices - common home appliances, factory equipment, radio transmitters, etc. One thing that does operate on a similar pattern is a telephone. Is it possibly a cordless telephone operating on an oddball frequency?

PlainBill

Think about something run by a thermostat, low control switch, or motion detector. They tend to cycle erratically. Things like a furnace, electric heater, water pressure boost pump, pool heater, demand water heater, sump pump, etc. There are also some uncommon devices that cycle. Negative ion generator, parking lot light controller, external HDD or NAS boxes, motion detector operated devices, iPhone background sync, etc.

However, I've been fooled before with this pattern. I was looking for such things, only to discover that the interference was coming from a microwave oven at a local eatery. During lunch, the microwave ovens were in use almost constantly. At other times, a minute or so at a time. Kinda sounds like the original description.

Dumb story: Many years ago, I had a very difficult time trying to find the source of short bursts of RFI. I tried for days and failed. Oddly, the interference seemed wide spread and appeared almost everywhere that I was sniffing. Eventually, the gears that drive my brain engaged and I discovered that the Motorola Bravo pager that I was carrying at the time, was the source. Argh.

--
Jeff Liebermann     jeffl@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann     AE6KS    831-336-2558

You can use an fm radio with a full length antenna. It will register in two directions used horizontally. Some broad band harmonics are best tracked down going from the lower freqs to higher. I tracked down some fm interference driving my car up and Down street. Strong interference near my house. It's all these cheap led switching current regulators I am using. I still have not tried to filter the outputs. I got wiring all over the place.

Greg

I have to check out my car radio too. I haven't heard any interference on it, but like I say, it comes at various times. often from 2 to 9 in the morning (and I don't commute regularly, and even when I do, I'm only in the car near my house for a couple minutes.)

It's the curse of the electronics age.

The furnace would correspond to the end of the night, and the beginning of the morning, which are common times for this. . At the end of the night, it's cold for the night thermostat setting, and at the beginning of the morning, it has to get hotter yet.

In some ways my neighbors are very friendly. Most will answer the door at 9PM. OTOH, when I asked a couple to see how their new furnace was installed, they looked at me strange.

I wouldn't have nerve enough, as someone suggested, to ask one to turn off all his power, certainly not unless I had narrowed it down to his house.

Definitely does this even when there hasn't been any rain. I'm literally the lowest house in the n'hood**, and would have heard my sump pump when I was hearing the basement radio make the noise.

**And the way it works out, it's 200 yards or more to any house outside the n'hood, all of which are also higher than I am. .

Dang, I only rejected one from your whole list.

Maybe I should go look for lights on when it does this in the middle of the night. That's one thing I might do.

There are no dumb questions or dumb stories. Only dumb people.

:~) Oops, I shouldn't bite the hand that feeds me. :~)

The hams can be very helpful if properly approached. Much depends on the available time, talent, experience, and hardware.

I can't tell from here. The problem is that the occupied bandwidth of an FM station with HD1 and HD2 sub-carriers is more than the assigned bandwidth:

Just read the first two sections, as the rest is all about fixing the resultant noise.

Reminder: Please make an MP3 sound clip of the noises.

Identifying Sources of Radio Frequency Interference Around the Home "

"

Hint: Assumption is the mother of all screwups. Test your theories and guesswork, even if you think it's improbable. I've been wrong and surprised more times than I can comfortably admit. That's one reason my domain is called LearnByDestroying.

--
Jeff Liebermann     jeffl@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann     AE6KS    831-336-2558

That will take me some time. I first have to find my Sanza Chip, or Clip,or whatever it's called. It does record iirc. I've been sort of looking for it for months, but now I have a reason to look harder.

The radio next to the computer has reception problems with these stations, so the noise is muffled and only recognizeable because I heard it on the other radios. Tonight I tried to fix up two AM/FM clock radios, but only got the AM working on each.

I also have a 40 year old cassette recorder that probably works fine, unless it doesn't I guess I coudl use that and then play it for the computer mike. (I have a great computer mike. )

I'll check these all out.

LOL. Okay. I'll do my best.

Let's look at your list:

A thermostat - refrigerator, freezer, or heating / cooling tends to cycle at a fairly constant rate, at least for the majority of the time (an exception would be when a large amount of food is added to a refrigerator, or a freezer, or when the set temerature of a thermostat is changed). A motion detector would operate at erratic times, but not for only 10 seconds.

Again, these would tend to operate on a regular cycle except for an 'on demand' water heater. However, the 'on demand' heater fails the 'on for one hour ' parameter.

Again, these devices fail either the '10 second' or 'one hour' parameter.

PlainBill

I wasn't thinking of an appliance as much as an HVAC system that has a time adjusted thermostat, and plenty of walk-in or walk-through traffic. I've worked with a cold storage warehouse where the cooling system would cycle as you describe as long as nothing was going in or out. However, when large containers of vegetables went into the warehouse, the cooler would run for about an hour before it started cycling evenly as you suggest. Same with HVAC system in areas with heavy foot traffic.

That depends on what the motion detector is running. I'm thinking more like a security DVR. When my cheap eBay piece of junk security DVR detects motion, it starts recording continuously for about 5 minutes. If multiple cameras detect motion, with some overlap, it could easily end up recording for hours.

There are motion detector lighting systems that work this way. For example, a local eco-friendly business saves electricity by not having the parking lights on unless it first detects motion. The lights are timed to stay on for approximately twice the time it takes to walk across the parking lot. I think that's about 4 minutes.

The on demand (tankless) water heater is very erratic. However, I will admit that it doesn't run for very long after the water is shut off. That's probably not it.

Electric heaters are much like the HVAC system. It really depends on what's going on in the house or office. If there's heavy traffic, the heater will cycle erratically. If it's a stable environment, it will cycle evenly. If someone left a window open, it will cycle at the whim of the wind.

Water pressure booster pumps are to get the water pressure up to about

30 psi minimum. They operate much like well pumps. If there's a demand, they run. If there's no demand for water, they don't run.

Sump pumps might be a stretch, unless they're dealing with a water leak that is also erratic. Add sewage pumps to the list for those with toilets below the sewer or septic level.

I beg to differ. One negative ion generator I had to deal with was purchased on eBay and apparently had never bothered to pass FCC Part

15 radiation testing. It wiped the entire HF band. Oddly, it wasn't the ozone err.... negative ion generator part that was generating the RFI. It was the motor that pushed the air through a HEPA filter. The motor would run whenever the device detected motion in the room as an energy saving feature. I think the hysteresis was about 2 minutes, but I'm not sure. If someone was in the room, it would easily run for an hour.

I know a bit too much about external USB HDD drives and NAS boxes from my day job. Usually, they just sit there doing nothing. However, if the owner has it setup to do either continuous or scheduled backups, it will run erratically according to the program parameters. The 10 second cycles could easily be some manner of continuous backup program, such as Memeo, which comes with WD drives. Memeo sends a copy of any file that changes on the computah to the external drive in short bursts, when the machine isn't busy. That takes a few seconds. The 1 hr run could be a more complete backup, or an image backup. Same with the NAS storage box, except over the LAN instead of USB.

--
Jeff Liebermann     jeffl@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann     AE6KS    831-336-2558

I have to say, this sounds like the opening scene from a murder mystery. Only cars are big enough to start the lights. The woman parks the car, away from the entrance so other cars won't ding hers. She walks to the store, is almost there, remembers sometihing in the car and has to go back, and on her second trip to the store, the parking lot lights go off, and she hears footsteps behind her. We only see her legs and his legs, and soon they are both running.

In the next scene, there are a lot of police standing around.