EMI / EMF / RFI radiation problems...? Wasn't expecting this...

Massive Master

www.massivemastering.com
Didn't really know where to post this so I figured this was the best place.

So I'd imagine most here know that I'm a mastering guy. I'm also a long-time radio enthusiast with various band licenses going all the way back to the 11m Citizen's Band back when you needed a license for that band. Recently passed the FCC amateur radio "General" class exam, which I'm pretty happy about.

As one would probably figure, my mastering room is also my "radio shack" (that's where the place got the name). I'm not using "serious" power in here -- Mostly only on 2m and 70cm frequencies with maybe 15-25w of Tx power. Now that I've passed the General and I can work on HF, that might change soon. But that's not the subject. ANYWAY ---

One thing I do rather frequently here (and shame on you if you don't) is calibrate - or simply confirm calibration of the system. Various sines / sweeps and what not through the chain making sure the noise floor is where it's expected to be and that L/R match to within ridiculously picky specs.

With the radio stuff in the room, I occasionally transmit at various frequencies and various power levels to see how a "silent" chain will react -- Usually a HT (handy-talkie, what most would call a walkie-talkie) at maybe 5w PEP, wandering around the room and looking at the meters to see how much RFI (radio frequency interference) sneaks into the chain. It's not much - But there's no doubt, when I'm working on something in here, I'm not transmitting. You can see it on the meters when I key up. It's not the fault of the (otherwise ridiculously quiet) chain - It's just a fair amount of EMI/RFI at very close proximity to the gear. I totally expect that there is going to be some amount of radiation that affects the integrity of the audio signal to a small extent. And although it would be totally buried by a super-quiet audio signal, I wouldn't want it on *my* album, so I'm certainly not going to subject yours to it.

To that end, part of my calibration "suite of tools" is a software defined radio (SDR) that presents me with a waterfall spectrum analysis of various frequencies. Originally (and usually), I just used it to listen to frequencies I didn't have transmit privileges on. But I quickly found out that it was a very handy tool to find sources of RFI/EMI that could leak its way into the system. You can't fix what you don't know about - and if you need a ferrite choke that works at a particular frequency because a washing machine next door or a nifty lamp in the next room is creating interference in your chain (true story), you need to know what frequencies you need to filter out. You'd probably be shocked (no pun intended) at the amount of electromagnetic interference that might be occurring in your space from things like LED lights and video monitors.

So last week, I was tuning in to a specific 2m repeater for a "net" (that's basically a group of radio users who check in to a net controller who "conducts" traffic from there) on 146.470 MHz and found the band to be "stomped on" -- It seemed as if someone was keyed up, transmitting an otherwise silent signal (a FM carrier with no modulation), which was being transmitted from this repeater around 35 miles away. This wasn't the first time I caught this anomaly on this particular repeater and I figured it was long sessions of some form of digital communications going on. This time however, I knew there was supposed to be a particular net. Being FB friends with one of the people who I figured would also be on, I said "Hey - what's going on? Someone is Tx'ing silence? Been there for 30 minutes" and she replied "??? The net is going. I'm surprised you haven't checked in yet."

SOOOOOoooo -- Loaded the SDR on to the main audio machine (it's a "dongle" receiver with a remote dipole antenna that connects via a support program) to find out where this interference was coming from and POOF - It disappeared. Dammit, foiled. Everything was fine, checked in to the net, all was wonderful. Until the next day when it happened again...

Loaded the SDR and POOF - It disappeared. Again. Okay, now I'm wondering WTF is going on here. Watched my 2m receiver and rebooted the computer. Rx (receive) indicator lit up (again, strong carrier and no modulation) and then went out as I saw the audio meters playing the "Windows" sound. Then it lit back up again. So I loaded an audio file into WinAMP or what not and POOF - It disappeared.

THAT RF RADIATION IS COMING FROM MY AUDIO COMPUTER.

Did just a whisker of experimentation and had 5 or 6 people on a different repeater throwing theories and suggestions at me. Booted again, saw the signal again, Windows sound no signal, then back again. Figured maybe it's a drive or something so I decided to start unplugging things to see if I could make it disappear. First thing I could reach was my USB to AES interface.

One shot / one kill. Signal immediately gone. Rebooted again to get the signal back and *power cycled* the interface. Gone again and stayed gone. Repeated this a few times to make sure there were no anomalies and I was "in charge" of the situation.

So on the "good news" side, this signal, that I never would've known about otherwise, has NOT affected the audio quality in the system. As soon as the device is "in use" by playing audio, the interference stops. But lemme tell you something - To "full quiet" a signal from a fairly powerful repeater takes a little Tx power. So to find out what I was dealing with, I hooked my SDR up to a laptop, rebooted and saw this relatively scary sight:

MiniDSP_U-DIO8.jpg

That is a BIG F'ing peak at 146.763 MHz. (the display shows 146.764 - long story) which was totally overtaking the signal that I was receiving at 146.760. There were others in the 136 MHz range and I assume plenty of other harmonics that I didn't have time to track down (takes a reboot of the computer and then a reboot of the device to confirm).

Next step at this point is to get another HAM buddy with a directional wattmeter out here to find out if that's a "dangerous" amount of RF radiation. When I'm using certain (usually really cheap, Chinese mfg'd) radios, I can feel the heat in my face during long conversations. I don't *think* I feel anything like that with this, but this device is a few feet away. Still, that's a pretty darn strong signal. Especially for something that shouldn't be transmitting anything at all.

I've contacted the manufacturer - FTR, we're talking about a MiniDSP U-DIO8 here - about the situation and they seem to be open to trying a few things because they can't replicate the situation there (I have to wonder if they have a SDR lying around, but maybe they do). And also FTR, the SDR in question is the RTL SDR USB with the RTL dipole antenna. If you don't have one, you probably should. It's a blast to listen to broadcasts and transmissions from all over the world that are passing through you anyway (RF is non-ionizing radiation, so it's not turning you into a monster or anything) and it's absolutely a wonderful tool for finding miscellaneous sources of RFI/EMI in your studio.
 

miroslav

Cosmic Cowboy
I'm not familiar with the wide range of radio equipment you referenced...but just to be sure I understood your problem & solution...it was the USB to AES interface causing the spike?

I have an RFI/EMI meter...and I'm sure if I brought it close to my PC audio tower, I would see a higher reading than with the computer off. I've done it with my laptop, and for sure...there is a good amount there...but nothing like when I turn on my microwave oven.

I've been telling folks that they need to check these things in their living environment, considering that everyone is now blanketed with 24/7 - 5G WiFi, not to mention their own local WiFi tranmissions...and not so much for any audio interference, but more for health reasons.

Do you have a new "smart" digital electric meter...?...those things are also transmitting WiFi 24/7, every few seconds, and emitting EMI because of their switching relays as they convert the analog electricity to digital for the meters. I had them remove my "smart" meter, and just put in a basic digital (they won't put back the old analog meter).
 

Massive Master

www.massivemastering.com
Yes - The USB->AES is giving off impressive amounts of very narrow-band RF. And yeah, "smart" meter. That's probably where those AM bursts are coming from every 30 seconds or so. I should have a look at that...
 

miroslav

Cosmic Cowboy
Yes - The USB->AES is giving off impressive amounts of very narrow-band RF. And yeah, "smart" meter. That's probably where those AM bursts are coming from every 30 seconds or so. I should have a look at that...

Not sure if they offer it in your area...but my power company had "op-outs" when they were installing their latest smart meters last year. So I opted out, and they didn't install their 24/7 two-way WiFi smart meter, and I also had them replace the existing "semi-smart" meter, which just transmitted a signal every 30 seconds so the meter guy could sit in the vehicle, and read the meter from there with a receiver.
Now I have just a basic digital...no transmissions.

I stood outside near my transmitting meter with an EMI/RF meter, and every 30 seconds there was a huge spike...now that's gone, but all of the digital meters, even the non-transmitting, still come with switching relays to convert the AC to DC for the meter...and those relays dirty up the AC coming into your building, not to mention, the dirty electricity causes motorized devices to draw more power...so you end up using more electricity.

Progress... :)
 

rob aylestone

Well-known member
The power output looks very high but it's also very narrow, so probably in RMS values, it's quite small. To quantify it you need to compare it to a known power level and then use attenuators to bring that down to match the signal strength of the spurious signal. My own experience is that for some reason SDR receivers using the dongles appear to hear narrow sources unrealistically stronger. Looking at the spectrum display of my own one, many of these big obvious spikes are totally unreadable on a typical portable of decent quality, yet they're clearly on the screens. Your's does seem to be quite potent enough to wipe out the local repeater - but milliWatts will do that to a microwatt signal from even a closest repeater. I'm not sold on the heating effect, my opinion being that with non-ionising radiation you need a lot of power to cause grief.

However, I've discovered how RF noisy so much of my audio equipment is - wall wart power supplies are the worst, but my Kong Triton is visible on the SDR.

My own issue with RF is the reaction of various bits of kit to DMR. My studio is quiet when I use a portable on UHF or VHF, the tiniest pop when the PTT is pressed, but with DMR, it sounds like a stream of motor boats have burst through the speakers with a popping, purring noise that is very loud. It's also different with every radio. I've got quite good at telling TDMA from FDMA, and mototrbo from other DMR. It's nasty stuff.

I've had a full licence here in the UK since 1980 and am taking my marine exam on Monday, as I've had a marine licence for ten years and only realised that I should have taken a test - which I never did!
 

Massive Master

www.massivemastering.com
Well good luck on your test -- After being on (accidentally?) for 10 years, you should probably ace that one...

And sure - I'm not expecting this signal to be super strong - Just surprised that it gives me "full bars" on the Rx meter on the radio. As far as the heating effect, I'd imagine not. But hey - if you're not sold on it in general, gab away for 20 minutes on one of those Baofeng things with a whip. You'll feel a "sunburn" sensation on your face and a rather uncomfortable feeling of your eye (whichever is closest to the antenna) getting hot. I hardly ever touch them anymore. But yes -- Wall warts, anything that's a charger, in my case, the washing machine (un-friggin'-believable what that thing kicks out on RF -- a 50,000 watt AM powerhouse with antennas just 5 or 6 miles away has no chance against my Kenmore washing machine during the rinse cycle).

DMR... I'm not sure if I ever had the gear hot when I was DMR'ing my way around... But not that I know you're on DMR, I'll have to keep an eye out. I actually try to hit (UK 2350?) here and there but I don't think I ever raised anyone who wasn't also "just visiting." I do occasionally hang on the Isle of Wright Thursday night net on GB3IW via EchoLink... Nice people.

Maybe see you OTA some time -- KD9TAC (although I recently upgraded to General and I put in for a different callsign so I might very well be N9IJS at some point soon). :thumbs up:
 

ecc83

Well-known member
All MOST interesting chaps! 'Ham' radio is a branch of electronics I never got interested in, dyed-in-the wool audio me but I am very interested in those USB receivers? Just found loads on 'Zon and they seem to be around £25-£30 and up. Can I get something decent for 30 quid?

My early days in servicing WERE influenced by RF! Living just a few clicks from Daventry and Rugby I had a lot of 'fun' keeping it out of amps and such once Silicon transistors arrived. Then we had the merry chase for for the Rubber Duck brigade and their burners!

I worked with a chap decades ago and remember his call sign, "G3YOD" love to know if he is still alive?

Dave.
 

rob aylestone

Well-known member
I always fancied my callsign for my van, but G4RMT was on somebody else's car, but as I spend 3 months each year (or did) in Northern Ireland, I just got G14RMT, which as 1is I on the plate, is correct form me while I'm there. Neat!
 

Massive Master

www.massivemastering.com
All MOST interesting chaps! 'Ham' radio is a branch of electronics I never got interested in, dyed-in-the wool audio me but I am very interested in those USB receivers? Just found loads on 'Zon and they seem to be around £25-£30 and up. Can I get something decent for 30 quid?

My early days in servicing WERE influenced by RF! Living just a few clicks from Daventry and Rugby I had a lot of 'fun' keeping it out of amps and such once Silicon transistors arrived. Then we had the merry chase for for the Rubber Duck brigade and their burners!

I worked with a chap decades ago and remember his call sign, "G3YOD" love to know if he is still alive?

Dave.
The unit I use is the RTL SDR dongle - Came with everything - I dipole with two sets of whips (one for damn near everything plus a shorty set for really high stuff), antenna lead, extension, antenna mounts -- I think it was $35 USD. A whole lotta fun for $35...

Can't find anything on your buddy - Except that I assume his name was Peter and he was pretty active in the 80's.
 
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