AM Radio Frequencies appearing in all of my studio gear

[davidcbeaman]

I recently moved into a new house, and after setting up all of my equipment I noticed that I was getting a pretty strong AM Radio signal on everything:

Otari mx5050 8 track tape machine, Soundtracs Solo Midi 16-8-2 console, Focusrite Clarret 8PreX, and even my bus powered Focusrite Scarlett 2i2. Same radio station across the board.

All my equipment and cables are grounded and the power outlets in my house are grounded. I have tried swapping cables, microphones, headphones, adapters, power cables, and I've even tried reorganizing/rearranging power and signal cables. I've moved everything between every room in the house and no matter where I set up I'm still getting the signal. It isn't just coming in from my headphones or direct monitoring, because this radio signal is tracking onto my tape AND into my DAW.

After some research I found that I live pretty much across the street from the tower for WCRT Bott Radio Network 1160 AM. I confirmed that is indeed the station I'm hearing.

Is there anything I can do about this? The only help I've found online was the usual cable-swapping/ grounding advice, but I've already ruled those things out and this is across every piece of recording equipment I own, across every room in the house.

After crossing off a massive troubleshooting list, I have to believe it's not my equipment. Everything worked fine before I moved into this place.

Obviously I can't just move houses, is there a solution here?

 

[rob aylestone]

With RF interference like this, it could be best to contact first the FCC. In the UK, we have OFCOM, and they have an understaffed and underfunded department who are real experts at this sort of thing - but, residential 'victims' are low down the pecking order. Interference to essential services comes first. They will here also refer you to the engineering department of the broadcaster, who actually have a licence requirement to minimise interference. AM interference was very common because of the simplicity of demodulation.

The snag is that remedial action is always just filters - low pass. If you are able to find the contact for the radio broadcaster's engineering department, they will have many potential solutions for you, I'm sure - BUT - only the engineers, and getting to them can be tricky.

Two things are happening, direct radiation into vulnerable equipment. New equipment has probably not even been tested for RF immunity as AM stations are reducing in number, and higher frequency FM and digital interferes less!

Direct radiation gets picked up by floating grounds, speaker cables, computer cables and you might find a local ham radio club who have some older experts. Chokes are common solutions for cable induced interference. Circular ferrite rings, or even the speaker magnets from old damaged PA speakers. Wrap a few turns of the cable through them and this produces a low pass filter that blocks RF energy on the cable. This kind of interference can go direct to susceptible devices - usually the ones dealing with low level processing that contain amplifiers - so our pre-amps, audio processors and effects units. Plastic cases and 2 conductor mains power or low voltage external PSUs.

The other main type of RF interference gets in via the house wiring. Not common with underground services, but so easy with overhead power cables. A damn great long cable working like an antenna, and if your mains power has the RF from the AM station superimposed on it, that is very difficult to manage and almost all your kit is connected to it.

It will help if you can determine where it gets into your system. It's a pain, but you have to start with the monitors and work backwards. Basically, disconnect everything and connect and power things up one at a time. So start with the monitors/amps and see if they are clean. Then start to connect everything part by part. Add your interface, check for interference. Then turn on the computer, check again, then connect the computer to the interface, check again. At some point you will start to hear the problem. That's the first fix it point. You then try the filters and see if you can cure it. Then move on. It will take ages and have many blind turns.

Often, you find one device that is making it seriously bad and lots of items that do it just a little, but many littles add up.

At best, the radio station will perhaps give you a few commercial filters. Possibly, if it's overhead cables the culprit, the supply company might help. If it's coming through the ether, through your walls, then you can foil wrap your room, and even windows with removable panels, and run the gear from UPS - the type that are essentially inverters and batteries. Sufferers usually report vast reductions are possible but rarely total elimination. Remember Lucille Ball? She always maintained she could hear radio through her fillings. Many say this was impossible, but she was adamant, and there is science to suggest that it's possible, though unlikely. AM radio has always done this. AM radio in housing areas is unfortunate, but the station WILL be aware, and social media is very important to them ..............

 

[ecc83]

Hello David,
I can add little to Rob's excellent treatise except to say I think you are unfortunately in a very high RF field strength area and fixing the problems is going to be difficult.

Yes, ferrite absorbers on just about every cable and balanced cables everywhere. You might have to invest in some good quality audio transformers but I would have thought the station should help you with that. A possible solution could be CAT 7 cable which has shielded pairs and an overall screen.

But, in my experience external measures can only help so far, a complete fix usually needs filters fitted inside the individual pieces of gear and that of course has consequences for the possible impact on the equipment's performance and warranty issues. Not to mention the cost of getting the work done and finding an expert to do it.

Best of luck.

Dave.

 

[drtechno]

Obviously I can't just move houses, is there a solution here?

Yes, there is a solution to eliminate the spurious interference. But its not a cheap solution.
You buy copper screen mesh, attach it to the walls and ceiling (physically and electrically to each section of screen, and ground it. The inside door also must be covered with mesh and grounded if its not made out of steel that you add a ground wire to.

Here is a link to the copper mesh: https://www.metroscreenworks.com/pure-copper-48-x-50/

 

[rob aylestone]

Sadly, a Faraday cage is only good if you can prevent the RF getting in through the cables and metal pipes going into the isolated space. Mesh on windows is also awkward, but the worst thing with total screening like this is your phone won't work!

The thing with physical screening is that it doesn't actually have to be a close mesh to work well, as AM transmissions are very long wavelengths and Faraday screening is related to wavelength - as in how you can see into your microwave oven, but the RF cannot get out!

Many, many years back my actual qualifications were in radio frequency engineering, and the intention was to have joined the RAF - but things changed - but I did get to work in some very RF heavy locations, including for just a short time, an interesting job on the east coast near here in the UK. The US Government installed an over the horizon radar station (the Russians had a very good one) but it never worked properly and was abandoned. BBC took it over as a short wave World Service site and every service in and out was heavily trapped and choked because interference from one service killed the others. Their fun trick with visitors was to wave fluorescent tubes in the air and they lit up!

In our case here, the number one task is to find out which route the interference is using to get into the system.

 

[ecc83]

Sadly I think the OP is on a hiding to nothing here and should take up stills photography instead!

Dave.