[Fixed]: 43 MHz burst noise every 63us in the Lab, (How to find the source)? - Page 1
Forum section: electronics / general

author: HighVoltage
author_rank: Super Contributor
timestamp: February 10, 2015, 11:55:41 am
content: I have a very strange situation in my lab.First I thought it came from a high power 3 phase 400V frequency changer, until I looked at the details of the signal and turned the power to the frequency changer off. Actually I turned all power off to lab and confirmed the strange burst signal with a battery powered scope.Here is the situation:The scope is connected to a DC output circuit via BNC cableThe Scope probe is set 1:1The circuit is not powered on and works only as an Antenna for this burst signal.Every 63 us there is a burst of about 300 mV pk/pk on the scopeZooming in to the signal, shows the burst frequency of about 43 MHzMy question is, how to find the source.May be someone here with HF experience knows what kind of burst signal this is.I am in a business park in Germany with neighbors to the left and the right of me.Thanks for any suggestions.

author: tom66
author_rank: Super Contributor
timestamp: February 10, 2015, 12:10:57 pm
content: It's nearly 15.875kHz or the horizontal refresh rate of a CRT. It's a bit of a stretch but do any of your neighbours use old CCTV systems with CRTs? Or just CRTs in general? (PAL format... not monitors as they use different retrace rates.) The retrace return could potentially cause something like that... though that's particularly bad.

author: Ian.M
author_rank: Super Contributor
timestamp: February 10, 2015, 12:29:28 pm
content: I hope you have already tried putting *ALL* electronic devices on your person into a metal tin with a tight fitting lid or wrapping them in at least two layers of foil and putting them as far away as you reasonably can from the device under test.I'd start by confirming the signal is still present with a different scope or a spectrum analyser. Then see if you can pick it up with a small tuned loop antennae which will eliminate the possibility that the excitation is actually at a different frequency, but a semiconductor junction or metal oxide layer in your unpowered device is providing enough nonlinearity to act as a mixer. After that you are into what the radio amateurs call "foxhunting". Although you are at the lower end of the VHF band, HF foxhunting techniques are more likely to scale well to 43MHz. The transmitter may be distant so check for the signal outside the building and up and down the street a bit before you spend a lot of time looking for a local source.

author: hammy
author_rank: Unknown
timestamp: February 10, 2015, 01:52:53 pm
content: Quote from: HighVoltage on February 10, 2015, 11:55:41 amIn Germany you can call the "BNetzA" for such problems. (Search for "Funkstörungen + Bundesnetzagentur" with your favorite search engine.) You pay nothing for this service (in general).Good luck!hammy

author: mij59
author_rank: Frequent Contributor
timestamp: February 10, 2015, 02:14:44 pm
content: No rf expert, the signal is quite strong, so the source is likely to be very close.Maybe its the lcd backlight of the scope.

author: KJDS
author_rank: Super Contributor
timestamp: February 10, 2015, 02:22:36 pm
content: 43MHz is about 6m wavelength, so lambda/4 is 1.5m.You should be able to get that far apart with two scope probes with a couple of turns of wire attached. Move these around comparing the phase and you'll be able to tell the direction. Do some triangulation from a few places to work out where it's coming from.I do know someone who spent several months trying to remove some 15ish kHz spurs from the RF synth they were designing, which were coming from the CRT of the spec ana he was using to measure it.

author: HighVoltage
author_rank: Super Contributor
timestamp: February 10, 2015, 02:39:02 pm
content: Quote from: tom66 on February 10, 2015, 12:10:57 pmI did ask all the neighbors for old CCTV and other old electronics.They all claimed that there is nothing.I might have to take my scope to them to see if it shows up.

author: HighVoltage
author_rank: Super Contributor
timestamp: February 10, 2015, 03:18:38 pm
content: Quote from: hammy on February 10, 2015, 01:52:53 pmThanks, I just called the "Bundesnetzagentur" and they will probably come already tomorrow.What a surprise, a fast acting government agency.I am looking forward to their finding.

author: HighVoltage
author_rank: Super Contributor
timestamp: February 10, 2015, 06:04:12 pm
content: Quote from: mij59 on February 10, 2015, 02:14:44 pmI tried 3 different scopes, all show the same signal.If I wrap the scope and the DUT is Aluminum foil, the signal shows stronger on the scope.The if I ground the Aluminum foil to the scope BNC ground, the signal is gone completely.Thanks for all your suggestions.May be the people from the government can figure it out tomorrow.

author: electr_peter
author_rank: Unknown
timestamp: February 10, 2015, 06:06:18 pm
content: Handheld spectrum analyser + directional antenna + GPS receiver. Anritsu even has special SW for this.

author: donmr
author_rank: Regular Contributor
timestamp: February 11, 2015, 12:07:54 am
content: Clipping the ground lead to the tip of a common probe makes a nice loop antenna. You can move it around and rotate it to get an idea of the location and/or direction of the signal source.The 43 MHz part my be ringing in your circuit and/or probe.We had a signal like that one a bench just last week, it was a cheap wall wart power transformer.

author: envisionelec
author_rank: Frequent Contributor
timestamp: February 12, 2015, 06:12:13 pm
content: Perhaps some telemetry equipment is nearby?

author: SL4P
author_rank: Super Contributor
timestamp: February 12, 2015, 08:47:32 pm
content: Many years ago, we had nearby airport approach radar causing a repetitive pulse like this, but the repetition rate was much slower. Of course technology has moved on since then...

author: Gixy
author_rank: Regular Contributor
timestamp: February 12, 2015, 09:09:44 pm
content: Quote from: SL4P on February 12, 2015, 08:47:32 pmYes! I saw that 25 years ago. The radar pulses generated false read on magnetic disks as the reading heads were moving by themselves when the radar pulsed. We have been obliged to put all the computer centre into a Faraday cage. Good old times... Nowadays radars are digital so field levels are lower and frequencies higher, but who knows?

author: max666
author_rank: Frequent Contributor
timestamp: February 12, 2015, 09:19:19 pm
content: Quote from: hammy on February 10, 2015, 01:52:53 pmFunny, I remember people being afraid of them, when they saw those guys driving around in their vans, because they thought they would hunt down people who aren't paying "Rundfunkgebühr" (radio & TV licence fee). And would be able to tell if you're receiving a radio broadcasting.Who would have thought they could actually be useful to the general public

author: tszaboo
author_rank: Super Contributor
timestamp: February 12, 2015, 09:28:16 pm
content: Do you live close to Italy?http://web.tiscali.it/vcoletti/ref/43chan.htmlThey say 100Km, but 300mV is a LOT.

author: HighVoltage
author_rank: Super Contributor
timestamp: February 12, 2015, 10:41:44 pm
content: Quote from: max666 on February 12, 2015, 09:19:19 pmSo true, I remember those days and I had a very strange feeling, when I called them.Actually they called back today and confirmed an appointment for next week and will bring their van of equipment to find the source.I am looking forward to those "Beamte" and may be they turn out to be useful.

author: HighVoltage
author_rank: Super Contributor
timestamp: February 12, 2015, 10:47:04 pm
content: Quote from: donmr on February 11, 2015, 12:07:54 amNo, the 43 MHz is not part of my circuit at all.I can insert just a 50 cm wire in to the scope input and get almost the same signalCan you really get 300 mV Pk/Pk from a broken wall wart?I am no HF expert at all, but this level I am measuring seems pretty high.

author: HighVoltage
author_rank: Super Contributor
timestamp: February 12, 2015, 10:50:54 pm
content: Quote from: SL4P on February 12, 2015, 08:47:32 pmThe nearest big airport is about 10 km awayThe nearest high power over land lines are about 1 km away with cell phone distribution on top of the power line pillars.Otherwise I am surrounded by forest and farmland

author: hammy
author_rank: Unknown
timestamp: February 12, 2015, 10:57:45 pm
content: Quote from: HighVoltage on February 12, 2015, 10:41:44 pmMostly fairy tales.Quote from: HighVoltage on February 12, 2015, 10:41:44 pmI called the BNetzA twice for radiointerference from the neighbourhood. I wasn't able to work CW from 80m up to 20m any more. I was able to narrow down the source, but I was not able to get a responsible contact person.So these guys made it on the official way ... it took some time, several appointments ... but then they "cleaned up" the whole street. My amateur radio station is now in a very quite area, and my neighbours are far more sensitiv on this topic now!Give them a chance. They are very nice and helpful people. We had a couple of talks over some cups of coffee, quite impressive the stories they can tell!

author: ivan747
author_rank: Super Contributor
timestamp: February 13, 2015, 10:41:41 pm
content: Quote from: HighVoltage on February 10, 2015, 03:18:38 pmGotta love Germany!

author: HighVoltage
author_rank: Super Contributor
timestamp: February 25, 2015, 12:04:45 am
content: The official government people from the "Bundes-Netz-Agentur" finally came and analyzed the signal.They had a Rhode & Schwarz handheld spectrum analyzer with a really old antenna and walked around the building and neighborhood. It took them about an hour to locate the source in a different building, about 100 m away from my suite.The source was identified as a bad server power supply in a big business server rack.The company was advised to replace or repair the PSU.Well, I hope they will fix it and the problem is solved.The agency will come again in about two weeks time to check if the bad signal is taken care of.It was an interesting event and these people had lots of really interesting and funny stories to tell of their encounters.

author: tom66
author_rank: Super Contributor
timestamp: February 25, 2015, 12:06:56 am
content: That's great to hear, I'm amazed that they went that far. +1 to them for actually finding the source!

author: babysitter
author_rank: Frequent Contributor
timestamp: February 25, 2015, 12:55:02 am
content: Those guys once visited the digipeater i was co-sysopping years ago to check if we keep to our licensed parameters.They had a lot of stories to tell. Intersting was their car, too!Not one of those cliche VW busses with a fishbone on top, it was a car for covert operations.It was a big white Mercedes Combi with tinted glass panels which got new license plates regularly.On top there was a antenna unit that was camouflaged as a luggage rack with grandmas suitcase under a tarp.On the inside, the control unit was sitting in the glove box, which was also able to remote-control some of these slightly hidden fixed intercept stations. Due to the equiment weight in the back, it required a reinforced rear axle. Direction finding doesn't take long, they talked about single digit milisecond transmissions sufficient with that system.If called, those guys are very effective. But very expensive if the interference is your own fault.A shop owner next my workplace reported that they came due to mobile network interference coming from his computer shop and he was afraid that he made a badly radiating computer, but finally the culprit was his wireless phone which he wasn't responsible for, from a big german manufacturer.

author: hammy
author_rank: Unknown
timestamp: February 25, 2015, 01:01:06 am
content: It is not unusual to find the source for interferences up to 300m away.The owner of this power supply will get an letter about the issue they found. If it exceeds the limit, the owner is forced to fix the problem in a given period, otherwise the have to shut down the faulty device. It's the law.Don't worry. They follow the procedure and they do everything by the book. It is impossible to outrun the BNetzA!Cheershammy

author: VK3DRB
author_rank: Super Contributor
timestamp: February 25, 2015, 12:20:15 pm
content: Quote from: HighVoltage on February 12, 2015, 10:50:54 pmMy goodness, you Germans are lucky. Being surrounded by forest and farmland is a big bonus.Here in Australia, we have all sorts of interference, thanks to a government that is clearly out of control over imports from China and lack of funding to police the sources of interference. Today, no one cares much about interference except the victims.A neighbour door bought a Dick Smith "100% acrylic" PC case. When my neighbour turned the PC on, it caused radiated RF interference to a few houses around. I did complain to Dick Smith and ACMA (cc'ed them both) and the piece of rubbish was taken off the market. So at least they listened and actedeven though due to a reckless loophole in the law, Dick Smith wasn't actually breaking any law. That was 10 years ago.I once lived near Wangaratta for 13 years, about 8km away from the town. I built an 8 element HF LPDA on my 2 hectares (5 acres) that was erected 20m (60 feet). Ideally 1.5 wavelengths of 20m would have been better. But I couldn't complain. It was a brilliant set up, and there was virtually no local QRM except from my electric fence when it was on. The only QRN was atmospheric and semiconductor noise. Armchair copies were common. Those were the days.Incidentally Dick Smith did listen to the customer. He once sold "ANZAC COOKIES". What a stuff up. The word "cookies" was not in our vocabulary in World War 1 when Sesame Street did not exist. The correct term is "ANZAC BISCUITS" and that is what was baked for our diggers. I wrote to Dick Smith Foods alerting them of their blunder and they immediately changed the packaging to the correct term.http://en.wikipedia.org/wiki/Anzac_biscuitOne must admire the French for retaining their language and not have it polluted. The French are more patriotic with their language than most other European countries and Australia.

author: Phaedrus
author_rank: Frequent Contributor
timestamp: February 25, 2015, 04:11:05 pm
content: Acrylic PC case? Was he using one of these as well?

author: 3roomlab
author_rank: Frequent Contributor
timestamp: February 25, 2015, 05:39:38 pm
content: oh dang ... it would be really interesting if you video-ed this "hunting" event ! ... PSU noise 300mV from 100m away !i wish i have BNetzA here ... OUR national WIFI signal is TOOOOO WEEEEAAAAKKKK lol !

author: SeanB
author_rank: Super Contributor
timestamp: February 25, 2015, 06:50:22 pm
content: 300mV from 100m away, that is not a power supply but a very high power transmitter.Here years ago we had friends who were paid to talk on CB radio. Their call sign for official purposes was Poppa Oscar. That division though sadly closed with the PO spinning off divisions, it now is part of a regulatory body. I pay them, but they are way too overworked and way understaffed, along with other reasons.

author: Stonent
author_rank: Super Contributor
timestamp: February 25, 2015, 09:09:57 pm
content: Quote from: max666 on February 12, 2015, 09:19:19 pmPapers? Do you have your papers!? (apologies if that's a poor joke)Edit: Just remembered this movie scene..

author: HighVoltage
author_rank: Super Contributor
timestamp: February 26, 2015, 10:12:02 am
content: Quote from: 3roomlab on February 25, 2015, 05:39:38 pmWell, I did ask them, if I could video record the event, but they strongly declined. I was in their van and had a look at the instrumentation and external antennas but again, I was not allowed to take videos or still pictures.

author: HighVoltage
author_rank: Super Contributor
timestamp: February 26, 2015, 10:19:48 am
content: Quote from: Stonent on February 25, 2015, 09:09:57 pmI think those days are over. These two officials looked more like the guy in the van of"Enemy of the State"Long hair, and beard and nose ring. Really great guys and they knew what they were talking about and had a full understanding of their equipment.

author: atferrari
author_rank: Frequent Contributor
timestamp: February 26, 2015, 11:28:14 am
content: Very interesting thread.Is anything in a PSU of that type that justifies the timing and frequency of the interference? I know nothing about switching PSUs.

author: Mechanical Menace
author_rank: Super Contributor
timestamp: February 26, 2015, 01:42:11 pm
content: Quote from: VK3DRB on February 25, 2015, 12:20:15 pmMost of the French do not agree with the Academies refusal to adopt new words, especially seeing as the language as we know it isn't even 150 years old. Fake antiquity for snobs. So most of the French ignore them in their day to day communications.And their attempts at renaming things they didn't invent is also f*&king disgusting as far as I'm concerned.

author: HighVoltage
author_rank: Super Contributor
timestamp: February 26, 2015, 10:21:26 pm
content: Quote from: atferrari on February 26, 2015, 11:28:14 amActually this power supply looked high quality and was one of those redundant server PSU's in the 19" server rack.They said it must have radiated the 43 MHz burst in to the 230V AC power line. And then the power lines transmitted it through the building and across from one building to another.

author: NiHaoMike
author_rank: Super Contributor
timestamp: February 27, 2015, 05:23:08 am
content: I'm going to guess a cold solder joint on one of the EMI bypass caps. Probably one soldered directly to the mains connector, where the soldering is done by hand.

author: ivan747
author_rank: Super Contributor
timestamp: March 01, 2015, 11:30:46 pm
content: Quote from: babysitter on February 25, 2015, 12:55:02 amThat only happens in Germany.I have heard of you guys modifying every sort of vehicle to meet every sort of weird requirement your authorities have. For example, autobahn stuff, I heard of special BMWs and Mercedes with their speed limits removed and with reinforced suspention to be able to carry the radio equipment, supposedly.

author: babysitter
author_rank: Frequent Contributor
timestamp: March 02, 2015, 04:32:30 am
content: Quote from: ivan747 on March 01, 2015, 11:30:46 pmNo speed limits ever installed, actually. As in about every german car, which are usually only limited to structural/engineering limits. The legendary Autobahn has in no absolute speed cap I am aware of.Maybe the reinforced rear axle is only saving taxpayers money - you want those public servants of the more expensive type to arrive at the scene quickly

author: HighVoltage
author_rank: Super Contributor
timestamp: March 02, 2015, 09:02:44 am
content: High end powerful cars have in Germany a speed limit of 250 km/h installed but most of them go to 260 km/h.This is not a law (as far as I know) but a limit placed on the cars by the manufacturers.Of course, this limit can be removed and some cars come even without this limit.For instance, if you buy a "normal" fast Mercedes, it is limited to 250 km/hBut if you buy the same car as AMG edition, it has no upper speed limit installed.Some government cars that carry heavy video and speed measurement gear, have stronger suspension installed, so they can followsome speeders, even if they go pretty fast. And after they stop you, they like to show you the video that was taken of you speeding.Here where I live in Germany, the police constantly gets new cars and equipment. But other places that I visit, the police is not so lucky andhas really old equipment.The guys that measured the 43 MHz burst also complained that it takes fat too long to get new equipment.

author: ivan747
author_rank: Super Contributor
timestamp: March 03, 2015, 01:08:52 am
content: Quote from: babysitter on March 02, 2015, 04:32:30 amHuh? I heard some models have their top speed limited, I am talking about the speed limit on the car itself, which is removed in this case. Yes I have seen those segments of the autobahn with no speed limits, that's crazy, but in a contry like yours, it works out pretty much perfectly.-Ivan, who lives in the most deadly country for highway commuters, according to the Guiness book of world records, aparently...and it's sort of hopelessBack on topic now...I am still impressed they managed to pinpoint the source to one particular device in a particular building, that's great. Do tell us when the owners of the noisy power supply replace it.

author: ivan747
author_rank: Super Contributor
timestamp: March 03, 2015, 01:13:01 am
content: Quote from: HighVoltage on March 02, 2015, 09:02:44 amOf course, it would depend on every department's budget, but trust me, you are in a good position. I've heard you check the load weight on trucks as well and catch a lot of overloaded romanian trucks, unfortunately. I guess they are not aware of the importance that is given to that sort of thing in Germany,

author: HighVoltage
author_rank: Super Contributor
timestamp: March 22, 2015, 12:04:51 pm
content: Just to give this subject a happy ending ....The neighbor had exchanged the power supply in the server rack and after that the noise had vanished for me.Total surprise, the "Bundes Netz Agentur" came last week without an appointment and took lots of measurements and confirmed that the burst signal was gone.The case is closed for them now. I am still surprised how fast and professionally they acted upon my request.

author: SeanB
author_rank: Super Contributor
timestamp: March 22, 2015, 12:16:50 pm
content: You should ask him for the old one, to see what is wrong with it.

author: HighVoltage
author_rank: Super Contributor
timestamp: March 22, 2015, 12:36:37 pm
content: Quote from: SeanB on March 22, 2015, 12:16:50 pmI did already...Unfortunately the PSU was exchanged under warranty and returned to the manufacturer.

author: hammy
author_rank: Unknown
timestamp: March 22, 2015, 07:57:00 pm
content: Quote from: HighVoltage on March 22, 2015, 12:04:51 pmI am happy to hear that!

author: HighVoltage
author_rank: Super Contributor
timestamp: March 22, 2015, 08:53:02 pm
content: hammy,you were absolutely right a few weeks ago, when you said ....Quote from: hammy on February 25, 2015, 01:01:06 amGreat to know for the future, that the Bundes-Netz-Agentur is taking a simple request so seriously.