Please help me investigate source of radio interference in recording studio - Page 1
Forum section: electronics / rf-microwave

author: sonictooth
author_rank: Newbie
timestamp: January 20, 2024, 04:11:42 pm
content: Hello,I own a recording studio and since about a year ago I've been struggling with a very annoying electromagnetic interference when recording electric guitars. You can hear it in the attached files, it kicks in around 0:05 (I have attached an unfiltered version and one with a high-pass filter applied so that it's more apparent). It sounds like it's centered almost precisely at 8khz, with some modulated frequencies above that and a 6khz tone kicking in every once in a while. It's *really* annoying because it's very recognizable even when the guitar is being played at a reasonable (i.e. not too quiet) volume.I tried turning off *every* electrical device in my studio: computer, wifi, router, lights, AC, outlets, etc. and it's still there. As a last resort, I tried turning off the main power switch of my studio, thus disconnecting *everything*, and I connected my guitar to a battery powered speaker... and the interference was still there.I bought a tinySA ultra spectrum analyzer and I see some strange peaks in the 800mhz-900mhz range but I'm not sure how to interpret this data. Also, I wouldn't know how to use this data to find the source of the interference. As you can see, I know basically nothing about RF, etc., but I'm a quick learner and I'm highly motivated to get to the bottom of this.Any help would be greatly appreciated. Even if anyone could point me to more specific forum it would be really helpful (I tried asking on recording studio forums but it's too technical).Thank you!

author: Grandchuck
author_rank: Super Contributor
timestamp: January 20, 2024, 05:19:47 pm
content: Your process of elimination points to the guitar. The attached files are silent here?

author: A.Z.
author_rank: Super Contributor
timestamp: January 20, 2024, 05:24:04 pm
content: just a shoot in the darkpick a 1KpF/1KV non polarized capacitor and build an insulated probe, then connect one side of the capacitor (probe) to the TinySA and the other side to the neutral of an AC plug, then check the spectrum, repeat with ground and verify if your 6...8KHz signal is present

author: DimitriP
author_rank: Super Contributor
timestamp: January 20, 2024, 05:56:46 pm
content: QuoteUsing the tiny SA, did you use the guitar cable as an antenna ?When you turned "everything off"...were cellphones/tablet/ apple watch left outside the building / off / airplane mode?Did you turn everyting off one by one or did you hit the main breaker switch ?Guitar, cable and battery powered speaker. Have you tried it outside the building ?Does it happen with more than one guitar and/or with more than one cable ?Is the hum present on the unfiltered mp3 considered "normal"?As for the building...what else is around you ? ie is this a stand alone building in the middle of a field (probably not).What is outside with an antenna?Weather station, traffic cameras, remote traffic lights ?

author: LaserSteve
author_rank: Super Contributor
timestamp: January 21, 2024, 02:36:35 am
content: There are many PC and Mac based audio spectrum analysers that talk to sound cards. May we see a audio spectrum from the console please of the guitar. Type of pickup in the guitar? Any active circuits in the guitar? Any diode based clippers in the guitar?This my "Music from Outer Space" crazy checklist:What happens if you switch input jacks on the mixer?What happens if you use studio monitors or switch to headphones?Musical keyboard switching psus are notoriously bad for wierd noises. As are midi consoles. As are custom effects pedals / cheap pedals.Tried unplugging other stuff from console?take a piece of non-conductive material and push on the strings and listen. My church has a piano that sings at 440 due to a ceiling fan or one particular guitar is played. If the lid is open. Just an example of the weird stuff that can happen.Digital or Analog console? Ipod/Ipad for wireless console control? Test oscillator / audio effects turned on in console settings ? Phantom power on/off in that channel?[ My skill set is Rf , lab instruments, lasers, and sound for my church]Are you near an ocean or marine environment, any transmitter towers within 20 kilometers? [piccolo, hellscriber ALE, FSK, The Navy, Ocean Wave Monitoring using OTHR]Any cell towers cell sites nearby? [ODFM carrier]Just with one guitar? Active or passive direct box in use? Any effects pedals / stomp boxes around? Any new LED lighting?Active direct boxes powered by battery or wall wart?Any new fans/heaters/rice cookers/coffee pots/ motor speed controls / lamp dimmers / flourescent lamps ?Any new electric car chargers nearbyWhat kind /frequency of wireless mics do you have?Airport nearby [ILS, yes, this happened in my town at another church]If I suggest an RF bypass mod for the cable can you solder?Hint ferrite beads inside the connector and 100-500 pf bypass cap to signal ground.Are you in a shared building with other businesses ?Had an induction heater screw up a studio once, badlyEverything points to the guitar, but try, try, again.Even utility power meters chirp these days.My church is blessed with a massive multicarrier cell site. I feel for you, it has taken me quite a while to obtain a quiet mix.If you take it to another studio/home amp/ guitar store does it still sing with the annoying noise?Re solder all connections in guitar, if electric guitar with many potentiometers / caps / inducors disconnect parts one by one if possible.It would not shock me if you had a ceramic capacitor. in the guitar that was piezo-electric.Had your blood pressure checked lately/ear exam?I've had to sadly suggest hearing tests for more thenone musician. Twice I've been right, third time it was something else.Do you have access to an oscilloscope?If so set to 300 mV scale and connect to Guitar pickup?Inductive hearing aid loop nearby?Look with fresh eyes.Steve

author: VK2AZT
author_rank: Newbie
timestamp: January 21, 2024, 04:23:49 am
content: It's a digital communications signal.I would not be surprised if it is something similar to bluetooth or a remote weather station sensor.Do you have a security system that uses remote wireless sensors?The interference may not even be from your studio area, it may be from a nearby property.

author: darkspr1te
author_rank: Frequent Contributor
timestamp: January 21, 2024, 09:01:42 am
content: Quote from: VK2AZT onTodayat 06:23:49 amI was thinking the same, Maybe even the GAS/Power companies meter ? a lot are wireless these days.darkspr1te

author: sonictooth
author_rank: Newbie
timestamp: January 21, 2024, 09:23:41 am
content: Quote from: DimitriP on January 20, 2024, 05:56:46 pmNo, just the included telescopic antennaQuote from: DimitriP on January 20, 2024, 05:56:46 pmCellphone in airplane mode.Quote from: DimitriP on January 20, 2024, 05:56:46 pmTried both things, no difference.Quote from: DimitriP on January 20, 2024, 05:56:46 pmNo. I can try tomorrow when I'm at the studio againQuote from: DimitriP on January 20, 2024, 05:56:46 pmYes. Every electric guitar and bass I own and with every cable I tested (I have short, professional shielded cables)Quote from: DimitriP on January 20, 2024, 05:56:46 pmPretty much yes. Electric guitars are noisy instruments by nature. It's the high-frequency content that's driving me crazy.Quote from: DimitriP on January 20, 2024, 05:56:46 pmMy studio is in a crowded block of a big city (Rome, Italy). So... lots of stuff. That's why I'm trying to get help to pin point the possible source.Thank you very much

author: sonictooth
author_rank: Newbie
timestamp: January 21, 2024, 09:47:00 am
content: Quote from: LaserSteve on January 21, 2024, 02:36:35 amOK I'm attaching a screenshot. The 8khz bump is clearly visible.Quote from: LaserSteve on January 21, 2024, 02:36:35 amThe attached example was with a passive Telecaster with single coil pickups but the interference is there with every guitar and bass I own (humbucker pickups, etc.). I can clearly hear it even when connecting just a cable to the amplifier with no guitar/bass. I'm attaching a sample of the same issue with a bass guitar (fender jazz bass, bridge pickup only)Quote from: LaserSteve on January 21, 2024, 02:36:35 amI tried connecting the guitar to: guitar amplifier (one Fender, one Marshall), a battery powered speaker (Bose S1), my main audio interface that I use for recording (RME UFX+), other audio interfaces/converters I have lying around (Arturia 8Pre, RME Octamic XTC), I tried using various active or passive DIs... The whine is always there.Quote from: LaserSteve on January 21, 2024, 02:36:35 amThe studio is in a busy block of a big city so... It's definitely possible that there are cell towers nearby. Also I have lots and lots of neighbours. That's why I would love to have an idea of what I'm looking for here.Quote from: LaserSteve on January 21, 2024, 02:36:35 amCould you please elaborate on what you're suggesting here? I don't know how to solder but perhaps I can find a pre-made solution.Quote from: LaserSteve on January 21, 2024, 02:36:35 amYes I'm in a big building with lots of other apartments and business. That's why I'd like to have some idea of what I'm looking for before I start showing up at people's homes and workplaces asking them to turn off their stuffQuote from: LaserSteve on January 21, 2024, 02:36:35 amThe guitar was serviced and shielded by a guitar tech but I get it with multiple instruments (and even with just a disconnected cable).Quote from: LaserSteve on January 21, 2024, 02:36:35 amThe whine is clearly visible with a spectrum analyzer so I guess it's really there.Quote from: LaserSteve on January 21, 2024, 02:36:35 amI'm sorry but I don't have an oscilloscope at the momentQuote from: LaserSteve on January 21, 2024, 02:36:35 amNo.

author: A.Z.
author_rank: Super Contributor
timestamp: January 21, 2024, 10:24:11 am
content: some notesas for the scope, if you don't own one, since we're dealing with low frequencies, you may try thishttps://zeitnitz.eu/scope_enand, regarding the TinySA, you may use (e.g.) this softwarehttps://github.com/erikkaashoek/tinysa-saverto record the analyzer output and post it as an attachment (or upload somewhere and share the link) for others to analyze/checkalso, you may easily put together an antenna like the one described herehttps://www.arrl.org/files/file/RFI/Thompson%2520Noise.pdfand use it, with the TinySA to go hunting for the source, either inside or around the block

author: AndyBeez
author_rank: Frequent Contributor
timestamp: January 21, 2024, 11:22:59 am
content: How are you powering the guitars? Any pedals?Is there a 48V phantom power mode - the spike could be from a failing buck converter?Any pre-amps or EQ stages in the audio chain?Is the noise worse with the cables laid on the floor or does the noise fill the whole studio? I ask as I once noticed 'floor' interference from CFL bulbs in the apartment downstairs.Or is there a hot spot? Take a long xlr cable (with no guitar attached), make a few loops on the end, and use that as an EMI probe by moving around the studio.

author: Kalvin
author_rank: Super Contributor
timestamp: January 21, 2024, 11:42:41 am
content: It might be common mode interference signal that is picked up by guitar cable(s), and which gets then into your mixer.You may want to try something like this:0. Buy/loan three RFI snap-on ferrites that fit tightly around your guitar cable.1. Disconnect all guitars from the mixer.2. Check that the interference is not there.3. Connect one guitar into the mixer.4. Check that the interference signal can be heard again.5. Add one RFI snap-on ferrite around the guitar cable (at the mixer end of the cable, as close to the mixer as possible).6. Does the interference get reduced / eliminated?7. Add two more RFI snap-on ferrites around the guitar cable (at the mixer end of the cable, before the first RFI ferrite).8. Does the interference get reduced / eliminated?After that you might also want to locate the source of the interference, and fix the problem at the interfering equipment if possible.

author: E Kafeman
author_rank: Regular Contributor
timestamp: January 21, 2024, 04:20:07 pm
content: It is clearly a carrier at 8 kHz with some digital sidebands. Surely a digital source but can not recognize it as BT WiFi or cellphone. Attached a FFT for the noise and a soundfile AM with 8 kHz as carrier where modulation start at 9 sec..

author: Bud
author_rank: Super Contributor
timestamp: January 21, 2024, 06:20:17 pm
content: The suggestion with ferrite snap-on chokes on cables is easy to try and is definitely that you should do.

author: sonictooth
author_rank: Newbie
timestamp: January 21, 2024, 08:23:00 pm
content: First of all, I want to thank everyone for the suggestionsI just tried the ferrite chokes (I had a bunch of them lying around). Sadly, they did nothing at all.Tomorrow I will try to record the output from the tinySA and attach it here. Any suggestions on how to perform the scan? The interference I hear is centered around 8khz, but could it be a subharmonic of some higher frequency carrier? As I already said, I'm not a RF expert so I'm just spitballing here

author: A.Z.
author_rank: Super Contributor
timestamp: January 21, 2024, 08:33:27 pm
content: it's easier it's a higher level (2nd, 3rd...) than a sub harmonic, anyhow, I think you've enough input now to be able to go for a hunt and identification

author: rhb
author_rank: Super Contributor
timestamp: January 21, 2024, 09:46:47 pm
content: Make an H field probe 6 inches or so, hook it to the tinySA and go looking for the source. Dave has a video on how to make one. However, a piece of RG-402 bent in a loop with the center conductor soldered to the shield, but leaving the shield open is just as good and *much* easier.Good luck. Tracking down the source of EMI is a huge PITA.Reg

author: Kalvin
author_rank: Super Contributor
timestamp: January 21, 2024, 09:49:18 pm
content: Quote from: sonictooth on January 21, 2024, 08:23:00 pmQuote from: sonictooth on January 20, 2024, 04:11:42 pmIt looks like the interfering signal is able to couple to the guitar's electronics/wiring, and then the interfering signal is able to go out to mixer/speaker through the guitar's cable.As you have a battery powered amplifier, you could try what happens if you take your guitar and the amp outside the building. If the interference disappears outside, then it would suggest that the guitar is quite sensitive to some interference present in your studio.You could also try what happens if you attach the RFI snap-on ferrites at the guitar's end of the cable.If you move your guitar around in your studio, does the amplitude of the interference change?

author: DimitriP
author_rank: Super Contributor
timestamp: January 22, 2024, 12:00:23 am
content: Ok, forget the effects on the audio for a moment.Can you put together a vido showing the tinySA spectrum (spiking all over the place) in sync with the interfence being heard.Even if you don't put a video together, there should be a spike that stand outs, lasting as long and in sync with the audible intererence.You might have to limit the span of the TinySA so you are not looking at the entire spectrum at the same time.Also see if a 1nF or 500pF capacitor in parallel with the guitar input jack makes a difference.

author: BrianHG
author_rank: Super Contributor
timestamp: January 22, 2024, 01:10:14 am
content: I'm curious, if possible, what happens if you attach a thick wire from the rack-mount chassis to an earth ground tap, or, from the chassis to a metal grounding point on your guitar?It sounds like a harmonic leaking from a switching supply through that power-supply's class X and class Y filter caps. These caps may be dying, or not designed at a high enough quality layout.My above ground wire test will provide an additional grounding path for one of the 2 poorly leaking class Y caps if they are the culprit.

author: dobsonr741
author_rank: Frequent Contributor
timestamp: January 22, 2024, 01:15:58 am
content: Two tests with the guitar when on the battery powered amp:1. How’s the noise amplitude changes as you turn the volume pot on the guitar from min to max? Audible on min? Where is it stronger - in medium position or at the maximum.2. Is the amp grounded? If not, try grounding the jack’s sleeve. Is the noise changing?

author: AG6QR
author_rank: Frequent Contributor
timestamp: January 22, 2024, 02:39:55 am
content: If you could find a local amateur radio club, you might find some smart people interested in a challenge. You're getting good suggestions here, but things could go much faster if you had someone local to take some test instruments into your studio. Many radio amateurs are only interested in using their radios to contact other radio amateurs, but a few of them love the technical aspects of electronics, and they sometimes have some interesting experiences in dealing with unwanted noise.My Italian is only very basic, but I was able to find this website, which might lead you to a local group.https://www.aricrl.it/Buona fortuna

author: darkspr1te
author_rank: Frequent Contributor
timestamp: January 22, 2024, 06:42:47 am
content: Quote from: E Kafeman onYesterdayat 06:20:07 pmThis to me looks like the carrier TX of a keyless entry key for a car.that would be funny if you were carrying around the source.darkspr1te

author: m k
author_rank: Super Contributor
timestamp: January 22, 2024, 07:52:23 am
content: Maybe attenuation is easier than amplifying.Since guitar is not needed you can put stuff in a foiled box and start wandering.Opening the side can be a sensitivity adjustment.

author: E Kafeman
author_rank: Regular Contributor
timestamp: January 22, 2024, 08:05:32 am
content: A keyfob will not result in a 8 kHz carrier. In actual audio sample is it a continuously ongoing modulation, but less noticeable for part of the time.As it is a very precise 8kHz carrier can freerunning switched PSU be excluded. A psu do usually oscillate in range 50-150 kHz.Same for LED-lamps which even if they are PWM capable do not have this variable modulation behavior if it not is a flashing x-mas tree.A very important clue is that there are subharmonics at 100 and 300 Hz-> source is connected to 50Hz main power. As noise increases with long antennas (cable), a few meters in this case is not anything above 100 MHz a likely source. Do not think it is any RF involved at all.As it is a well controlled 8 kHz carrier is it very likely generated by a MCU.As it is easy possible to pick up is it a strong source.If all my assumptions are correct are many alternatives excluded.8 kHz, where is that a common used frequency that fits in above assumptions?There are many possibilites but it is a common frequency for controlling electric servomotors using a MCU and a powerful driver.A lot of current and a long wire between driver and motor and it is a very possible powerful magnetic nearfield transmitter with cable as loop antenna.It is just one of many possibilities but assume it is in that way, how to locate source using existing equipment?A loop signal is best picked up using a similar loop antenna oriented with broadside against source for strongest signal level.Connect a few meter unshielded cable winded as a 200 mm loop to a laptop with soundcard mic input and check signal using a free SDR software if 8kHz carrier direction can be found by rotating the loop antenna in different direction and then start to walk in indicated best direction. If signal then is getting weaker, walk in opposite direction.If it is a detected radio-signal is it most likely shortwave something. Long time ago was it not unusual to be able to listen to Radio Moscow while playing 75rpm records at tube radio. For that kind of reception was an unlinear detector needed, such as a tube.That problem is much less if using balanced cables and modern balanced amplifiers. A possibility is still guitar with integrated electronic circuit and a lot of unshielded pickups. It is however easily checked by connect a loop wire to a batterypowered laptop mic input. Less capable but maybe by TS better known software such as Audacity (Windows) or corresponding audio software can at least show if a specific 8kHz signal is picked up.

author: BrianHG
author_rank: Super Contributor
timestamp: January 22, 2024, 08:27:26 am
content: I just remembered something from my old engineering days in the late 80's when I was engineering audio sampling technology with mics / electric-guitar pre-amps.Do you have a CRT monitor anywhere near your audio equipment? This includes 1-2 rooms away.It can even be a small CRT such as some of those in vintage audio mixer consoles which had digital console display on them, or even old security cameras B&W monitors somewhere in the building. The monitor's Yoke Horizontal flyback would radiate a signal which could be picked up by they coils on the mics diaphragms. I used to get aliiasing tones (a lower harmonic tone) depending on sampling frequency and the monitor's 15.7 khz tone as well as a slight 60hz buzz fro0m the vertical deflection. The pickup on electric guitars were also particularly sensitive.The key to this problem is that there was no interference when using condenser mics which do not have a coil like the magnetic based mics.

author: Kalvin
author_rank: Super Contributor
timestamp: January 22, 2024, 09:12:52 am
content: Here is the spectrum and signal envelope when analyzed using using Audacity (File: noise_unfiletred.mp3).It looks like some sort of digital communication signal. The symbol rate is probably 50 symbols/s, and the total packet length is approximately 15 seconds. The modulation deviation is about +/-250Hz.1. The packet starts with 700ms preamble (length 34 symbols).2. 375ms tone/sync at 5.25kHz (length 18 symbols).3. 13.2 seconds payload (length 660 symbols).4. 550ms tail (length 28 symbols).5. Silence for 2 seconds.6. Faint remote signal at 7kHz for 2.6 seconds (Acknowledge?).There also seems to be a faint synchronization signal at 8Khz with on-off period of 0.125Hz ie 1/8 seconds (see the faint dashed line at 8kHz).

author: uer166
author_rank: Super Contributor
timestamp: January 22, 2024, 09:36:24 am
content: With such a low frequency, this kind of reminds me of some kind of industrial or grid-scale PLC on the mains.

author: Kalvin
author_rank: Super Contributor
timestamp: January 22, 2024, 10:06:00 am
content: Quote from: sonictooth on January 20, 2024, 04:11:42 pmDid you turn off your phone and removed your watch from your wrist as well?Does the interference get weaker when you move away from the guitar?Does the interference become stronger when you touch the guitar's strings, mic, or knobs?

author: sonictooth
author_rank: Newbie
timestamp: January 22, 2024, 10:39:31 am
content: Quote from: Kalvin on January 22, 2024, 10:06:00 amI turned off the phone and I have no smartwatch. If I touch the strings or I move away from the guitar I do not hear any noticeable difference.

author: Kalvin
author_rank: Super Contributor
timestamp: January 22, 2024, 10:48:25 am
content: Quote from: sonictooth on January 22, 2024, 10:39:31 amOk, good. Just checking.Did you take the guitar and the battery powered amplifier outside? Does it make any difference?

author: LaserSteve
author_rank: Super Contributor
timestamp: January 23, 2024, 06:33:02 am
content: They are trying to reach you about your Guitar's Extended Warrenty!Sorry to have not been of much help.Steve

author: sonictooth
author_rank: Newbie
timestamp: January 23, 2024, 01:50:42 pm
content: I built a portable contraption using a guitar pickup (single coil), a preamplifier, a line level recorder and some headphones, and I went around to investigate...To my surprise, the signal got WEAKER outside the building. But I was able to trace it back inside the building. My studio is underground, but there is still one level beneath my studio. On this floor there are some garages and storage units... The signal gets incredibly strong just outside the door of one of those storage units.Now I just have to find the owner and have a little chat...

author: A.Z.
author_rank: Super Contributor
timestamp: January 23, 2024, 06:32:08 pm
content: I just hope that the little chat won't be something like "te stacco 'n braccio e te ce pijo a schiaffoni" or along those "gentlemen discussion" lineswhatever, please... PLEASE ! Let us know about the source for that interference.Thank You

author: Jr460
author_rank: Regular Contributor
timestamp: January 23, 2024, 07:44:39 pm
content: Could it be some type of power line comms, such as X10 or Insteon, I think those are at 120KHz on the line

author: sonictooth
author_rank: Newbie
timestamp: January 24, 2024, 09:14:47 am
content: OK I did some more investigations and now I'm more confused than ever...The whine *definitely* gets a lot stronger when I move to the underground level (with the garage etc). But I'm not so sure about the precise location and it's not easy to investigate because there are lots of doors that I can't open. I'm not so sure about the "guilty" storage unit anymore because there is a power meter above the door and it's stuck at 0, so it's hard to imagine that there is electrical equipment inside.Another thing that bugs me is that in the underground level I do not see any spikes on the tinySA. Absolutely flat. Perhaps I'm using the wrong kind of antenna? (I'm using the telescopic antenna that's included).Another strange behaviour I observed is the following:1) Guitar into battery-powered speaker (*not connected to the mains*), main power breaker switch ON: I hear the noise2) Guitar into battery-powered speaker (*not connected to the mains*), main power breaker switch OFF: I still hear the noise3) Unplugged cable into battery-powered speaker (*not connected to the mains*), main power breaker switch ON: I still hear the noise4) Unplugged cable into battery-powered speaker (*not connected to the mains*), main power breaker switch OFF: the noise goes awayWhat does this mean? I'm really really confused. Could this point to some kind of power-line communication, like Jr460 is suggesting?

author: E Kafeman
author_rank: Regular Contributor
timestamp: January 24, 2024, 10:44:54 am
content: It is a very possible behavior. No related signal at tinySA is also very possible as I previously wrote.Irepeat :create a loop antenna such as I previously have described, and learn how to get correct direction by rotating it by hand.It is more time-effective to do things in a correct way.Use a software for reading of signal level. It makes it easier to pinpoint exact direction and compare signal-levels. It is 8kHz that is of most interest so focus on reading its level.It makes it easier to find signal source if some knowledge about typical possible sources.I have seen a bit similar problem as you know seems to be facing.A remote controlled roof ventilation-servo was controlled by a heating rregulator for the house and its electric equipment was placed in the cellar. As the electric driver was noisy did the cable all the way from cellar up to the roof act as an long antenna. At every floor was strongest signal located to a vertical cable duct with a lot of possible radiating cables.By switching loop antenna to a small loop, similar to a guitar pickup, with just very few turns of unshielded wire , was it possible to sniffing on each cable to find strongest main source and then follow that cable backward.This sniffing required that the loop was winded around each cable a few turns before reading signal level to get a reliable result as all cables was indirect antennas due to that they was placed in same duct and infected each other.You need to create a loop antenna for sniffing. For weak signals, make bigger loop, using a few meters cable.For nearfield pinpointing, use a single turn 50 mm long or shorter wire as loop antenna.Solder cable to a 3.5 mm connector, one end to ground/outer shield and the other cable end to center-pin.It is a very typical way to find this kind of problem by creating your own temporary loop antennas.Similar antenna description can be found at many websites by googling.Here a picture of a typical such loop antenna:https://hackaday.com/2021/05/21/simple-probe-sniffs-out-emi/Nothing complicated, any single wire can be used.Connect it to PC mic input and config SDR software use mic signal as input signal. Then tune this "radio-software" to 8 kHz. Rotate the antenna by hand to learn how to find exact direction.If signal is strong is a very common way to increase precision in direction finding to use antenna in an opposite way, rotate it to find minimal signal. It should then be possible to get precise direction within a few degrees as minim tend to be very narrow and sensitive for exact direction.Transmitting antenna can be very long and it can along its way infect other cables so careful reading signal levels and direction at different location can be needed to be able to find actual source in an effective way.Even electric power meters can sometimes contain equipment for these frequencies, 500-50.000 Hz.It is used for power metering and remote receiving of control-signals. Even if no power is passed the meter can it still be active and emit noise due to a faulty operation.Is it a new meter, installed/replaced in same time frame as when you noted this noise?Using a real small loop, and you will only be able to read any 8 kHz carrier near this meter.If possible, remove its fuses to check if the noise then disappear.If culprit is found to be the meter, call the electric company and tell them they have a meter that not is registering any power consumption and emit a lot of noise.

author: dobsonr741
author_rank: Frequent Contributor
timestamp: January 24, 2024, 03:16:51 pm
content: QuoteSuggests you have a strong EMI component that radiates from the live power wiring as an antenna.Also suggests the guitar cable could be getter shielded.

author: m k
author_rank: Super Contributor
timestamp: January 25, 2024, 07:12:44 am
content: Quote from: sonictooth on January 24, 2024, 09:14:47 amYou don't seem to believe what you've been told.The noise goes through almost everything, the rest it reflects.You have only one possibility forward, you need a directional measurement.Either you amplify one direction or attenuate all others.You know that your cable and amplifier setup will receive it, use that.Put the cable in afoiled potato chips bagand cut one corner open, more if needed.Now you have an inverted directional antenna, make it also so that you can point it up and down.E,potato chip bag is too thin, blocking 8 kHz is around 1 mm of aluminum, sorry about the inconvenience.Maybe you were active and tried different boxes and found something.In case your potato bag was effective the transmitted frequency must have been much higher, maybe 10MHz or more.

author: E Kafeman
author_rank: Regular Contributor
timestamp: January 25, 2024, 09:34:57 am
content: >Put the cable in a foiled potato chips bag and cut one corner open, more if needed.>Now you have an inverted directional antenna, make it also so that you can point it up and down.This is not based on any knowledge so you can neither have an experience that it is a functional advice.You is just mean trying to mislead someone with known false advises or is it it some kind of try to be funny, try to fool TS?How to make a directional antenna , directive in a single main direction, for EM waves is VERY well known.Simplest and smallest possible directional antenna using a metallic foil such as a potato chip bag is to use it as a reflector for a dipole. Effective smallest bag-length is then 0.5 lambda.For a typical potato chip bag is that around 500 MHz the lowest effective frequency resulting in a few dB directional gain and a few dB fb-ratio.However, this is nearfield mainly magnetic field so a potato bag is just as usable as a shoestring. Have you tried to make a strong magnet single directional using a potato bag?In actual case is it mainly a magnetic near field. At 8 kHz carrier is wavelength 30km. Your potato bag need to be at least 15 km long (10 miles) to be able to act as a halfwave reflector at 8kHz but it is not a effective directional gain until the antenna is in fare field, a few lambdas away. Fare field is then beyond 100km or 60 miles. It is a complicated long distance away to locate a noise source from.An antenna several km big in size is not either simple to use as handheld to be able to move it in different directions.That is why small loop antennas are to prefer as handheld search coils in a nearfield. A such loop is actually not a tuned antenna for EM-waves, it is more like a secondary winding in a transformer receiving mainly a magnetic field.Placing a coil inside a potato chip bag will NOT result in any usable directional effect at current frequencies of interest.Compare radio-antennas for longwave LF reception 10-300kHz. Have you seen any LF antenna with a single directional effect? There are actually a few of them, resulting in 1-2 dB directional gain below 20kHz.Grimeton tx antenna have a 1-2 dBi gain at 17kHz while being a relative short antenna. It is just 2 km long and its efficiency is as most around 5%. This gain is possible by forced individual phasing an array of antenna towers.A million potato chip bags not will add any additional directivity to this antenna.

author: AndyBeez
author_rank: Frequent Contributor
timestamp: January 25, 2024, 12:55:38 pm
content: I am wondering if being in a basement, there is something outside at street level; from the electric or telecoms utility. Maybe even a neon sign or a maintained/non-maintained exit light? Mains borne buzz does seem a likely candidate, but without a scope to take a look at the waveforms, it's really becoming anyone's best guess. To me, the preamp stage is acting as the EMI rectifier, but only having minimal informationDoes the interference fade if the amp is placed on the highest point of the building?

author: m k
author_rank: Super Contributor
timestamp: January 25, 2024, 06:29:42 pm
content: Quote from: E Kafeman on January 25, 2024, 09:34:57 amNo.But maybe the bag has no foil at all.Just remembered that here the bag should be trashed with plastic.So foiled box is better.Either you amplify wanted or attenuate unwanted, no difference, or there is but that's different.Here the source is possibly located, so attenuating has a good change.Though receiving something outside a building can mean that the source is something completely different.

author: E Kafeman
author_rank: Regular Contributor
timestamp: January 26, 2024, 06:16:02 am
content: >So foiled box is better. Either you amplify wanted or attenuate unwanted, no difference, or there is but that's different.False statements. Your electrical knowledge in this matter is just an empty bag.An antenna or pickup coil have no amplification as it is a passive device.You can not affect directivity at these frequencies in near field using a bag or a container of any kind. It is too small objects relative wavelength.Shielding electric field in any direction will reduce measured level in all directions.Shielding magnetic field is a different matter. It is very demanding as a magnetic field easy passes a through a metal sheet causing low attenuation.However can a magnetic field be redirected using metals under certain circumstances. Iron core in a transformer is a such example. It does still not affect directivity in any particular direction.Metal-sheets are ineffective attenuators of magnetic fields. Most common used material is mu-metal which is more effective shielding then regular iron plates.http://www.mu-metal.com/shielding-fundamentals.htmlIf making a cubic-meter-sized box with 100 mm thick metal walls leaving a narrow gap in one of the walls and placing a pickup coil inside this box will not result in any directivity in a certain direction for these frequencies, neither amplified or attenuated.

author: gb714us
author_rank: Newbie
timestamp: January 26, 2024, 06:40:45 am
content: Timely post.I'm new around here, but I'm not new to the problem that you're facing. I'm still trying to find the source of noise near my house. It's only getting worse for me.The people suggesting creating an antennae for picking up the noise are correct. That's probably the most effective way in finding the source.I bought a YAGI antenna to see if it picks up RFI. It does, but I'm not sure its the same as the one that my guitar picks up. I use a small RTL-SDR that I hook my antennae up to and try to find noise that way. It's a little involved, but it's interesting to me.Anyways, this youtube video is exactly what you need. I haven't gotten around to it, but it makes a lot of sense.

author: Jeroen3
author_rank: Super Contributor
timestamp: January 26, 2024, 07:33:42 am
content: Quote from: uer166 on January 22, 2024, 09:36:24 amI was going to say this. Your utility sends some PLC over the wires. You pick this up.Typical mains filters do not work in this range. You need sine wave filter. (basically transformers)I have read about an issue similar to this, where it was also a constant ~ kHz audible noise on gear where it was harmonics from a local sewer pumping station with VFD's.There is no regulation like EN50160 for the areas after a ~20th harmonic to MHz. So nobody really cares.

author: m k
author_rank: Super Contributor
timestamp: January 26, 2024, 08:29:18 am
content: Quote from: E Kafeman on January 26, 2024, 06:16:02 amYes.My guess was that the signal is weak and receiver is good.It's also easy to implement and it's also information if it doesn't work.Any other method for worse receiver can possibly give some information also.Though no idea what kind of signal strengths are usually needed for these kind of frequencies to go through buildings.But some idea of misleadings of differently attenuating signals here and there.8 kHz shouldn't be overly complicated to block.Maybe inverted noise receiver and then summing it to guitar signal.Adjusting before every stint shouldn't be too irritating if only one guitar is used.

author: MarkT
author_rank: Frequent Contributor
timestamp: January 27, 2024, 10:48:54 am
content: The skin depth at 8kHz in iron or steel is of the order of 0.1mm, so even 1/16th inch steel will shield well for 8kHz interference.

author: E Kafeman
author_rank: Regular Contributor
timestamp: January 28, 2024, 03:55:33 am
content: Yes electric field skin depth is rather limited and requires not any thick metal to provide electric shielding.Does this knowledge add anything of value in this case?Even a thin cable braid is sometimes enough to create a decent electric shield or in bigger scale, can a whole room be covered with metal creating a Faraday's cage. If no unfiltered cables are allowed to enter into this room can electrical noise level be kept low and the magnetic field will be equal streamed in whole room, why it not will be noticed or picked up inside the chamber by any cables as it will be same field in both ends of a cable ass long as it is kept inside the cage.For finding actual noise source is however electric field strength not particular interesting as it anyway is very weak and hard to locate in near field in opposite to a fare field source.Current noise source is a near field source dominated by its magnetic field for which a thick steel plate, a fraction in size of a wavelength, not will add any attenuation or reflection for the magnetic field.Fromhttp://www.mu-metal.com/shielding-fundamentals.htmlShielding does not eliminate or destroy magnetic fields, nothing does.A mile wide thick metal wall will not change that.That is why even an unusual thick metallic covered potato chip bag not will be of any use to provide antenna directivity at 8 kHz.

author: m k
author_rank: Super Contributor
timestamp: January 28, 2024, 12:26:00 pm
content: Ground level is weaker than underground.SA with dipole antenna didn't pick the 2nd floor underground signal.Later OP is confused, maybe with a 2nd equally strong underground spot elsewhere.Maybe somebody had only one wire and DC needed too much power.But 8 kHz went through just fine and heat pipe was enough for ground.Maybe ground is not connected at all and it still works.So original installation is generating an induction loop and all other loops of the building, frame and others, are transferring the signal.How much it's attenuating per hop, 10%, half?Can receiving XYZ-loops generate enough directional differences for meaningful testing without hi-fi level gear?Can multiwire guitar cable with one floating pair connected to inverted receiver attenuate the noise of later summed signal enough?

author: Bicurico
author_rank: Super Contributor
timestamp: January 28, 2024, 12:37:48 pm
content: Sorry, couldn't resist:

author: m k
author_rank: Super Contributor
timestamp: January 28, 2024, 06:52:35 pm
content: Maybe there are less heat pipes in Rome.I understand that everything singing near an AM radio station is always induction based.Also that it's always an acoustic thing between two singing and not singing materials.My intuition says that when signal strength is weakening enough it stops being induction based.But it still remains to be near field, since distance is the same.So electrical near field photon can be deflected just like any other electrical photon.But can that deflection result anything directional is another thing, my intuition says that it can, if resulting signal is weak enough.Selecting between right and wrong direction can still be difficult, but my intuition says that normal person's intuition will learn it in no time.If electrical near field signal "finally" goes through that foil then my intuition has failed.I understand that both can happen, but energy is energy, so why that 8 kHz photon is different if it's from near.Only rational answer is that the foil is not a deflector anymore, but isn't that then more like an induction, if not then how to define when it is.(I don't understand interaction differences of electrical and magnetic photons)Trying to understand what is weak.Hearing loop is something that some folks like to use.If memory serves few tens of meters of a loop can still be heard from outside of the house, but not far.In that case the loop is still higher than the receiver, so some of loop shape is still present.But I have no idea what kind of energy levels are regularly used in those loops, intuition says few watts tops.

author: E Kafeman
author_rank: Regular Contributor
timestamp: January 29, 2024, 04:04:02 am
content: Quote from: m k onYesterdayat 06:52:35 pmWhy not replace your faulty intuition with knowledge known since long instead of spreading false rubbish?Wave theory was made known by JC Maxwell 150 years ago and even simpler, Ohm's law, is known since very long. Why have you not heard about that or do you not believe that Ohm's law is reliable knowledge? Your intuition says something else?It is a bit unnecessary to use this thread to educate beginners that seems to refuse to learn and instead assume they can replace it with intuition but here are some elementary fact explained in a way that most should be able to understand.It is rather simple and we can start at DC! What can be measured, detected? Knowing U=IR and we can design tools to detect electric voltage or detect magnetic current. R is the resulting resistance of that circuit. R is not measurable as separate parameter, it is a result of measuring both U and I.For any power to be detectable are both U and I needed as we know by Watts law: P=UI. If either U or I is zero will P be zero.Saying that a signal can stop being induction based if it is weak enough as you do is therefore rubbish, fails at Ohm's law and Watt's P=UI. If the current is zero is there no power that can be detected, no voltage no current can be measured with a probe or an antenna of any kind and no resistance can be detected.DC does however not emit waves. For anything to radiate waves is AC needed and by then a current not in same phase as the voltage. It results two fields, electrical field and magnetic field with different phase for each field. Due to this phase difference is reactance added to resistance creating a complex value known as impedance.According to P=UI do we know that both these fields must exist if there should be any radiation at all. Just one of these fields can never exist alone as it not will produce any power.It is not so complex math to find that in far field is it a fixed relation between these both fields and just as for DC, R=U/I can we calculate field impedance to 377 Ohm for fare field (free space).In near field is it possible to adjust ratio between magnetic and electric field in emitting source. Whatever source impedance is adjusted to will emitted wave anyway transforms to 377 Ohm in far field.Electric field in near field is a chaotic field for which direction finding using in fare field directive antenna or electric shields not will be of any use as electric field will be very distorted.>But can that deflection result anything directional is another thing, my intuition says that it canA potato chip bag as electric deflector in near field at 8kHz is a really a totally nonfunctional poor idea and as I already previous in this tread have explained why and that a million bags not neither will be of any use must your intuition be a bit slow learner.There is nothing in electric theory that can be made weak and by then simpler to find radiation direction. Your intuition is reliable wrong also in that aspect.Instructive pictures at Wikipedia shows radiation in near field and fare field shows why electric direction finding not is a good idea in nearfield:https://en.wikipedia.org/wiki/Near_and_far_fieldAnimated electric near field:https://www.reddit.com/media?url=https%3A%2F%2Fi.redd.it%2Fcgmav1xjeow61.gifBelow text is borrowed fromhttp://www.iosrjournals.org/iosr-jeee/Papers/Vol7-issue2/M0728892.pdfQuoteKnowing some basic wave electricity and it will be obvious that a potato chip bag is not of any use for creating something with a specific direction gain for a wave frequency of 8kHz and it will anyway not be able to pick any direction in nearfield (100km). A potatobag is too small to add anything for a wavelength of nearly 40km.

author: Smokey
author_rank: Super Contributor
timestamp: January 29, 2024, 04:22:51 am
content: Doesn't the tinysa have a lower frequency bound of like 100khz? going to be hard to see 8khz with a highpass at 100khz.A recording studio that is also an anechoic chamber would actually be pretty bad ass. It already looks like something you would see in a music video:8khz reminds me of a servo drive pwm frequency. That would probably be audible though if you were near the motor.

author: m k
author_rank: Super Contributor
timestamp: January 29, 2024, 08:37:32 am
content: Quote from: E Kafeman on January 29, 2024, 04:04:02 amHow to make a Faraday cage around that amplifier and cable?E,Just saw a picture of different thicknesses and frequency.Blocking 8 kHz was around 1 mm of aluminum, different alloys were not separated, copper was about the same.I didn't know that, clearly a bit more than a potato chip bag.I know that one series of plastic cased device had to be coated for better noise reduction, but importance of used material was news.No wonder some meter covers are so thick.Local electricity distributor has made a test for attenuating 400kV substation electrical field for workers.They used 1 mm steel wire mesh made faraday cage and attenuation was more than 95%.