Picked up a radio station the other day

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SRR

SRR

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I think I picked up a AM station not sure on that could have been FM, anyways was coming thru my ART DPS II connected digitaly to my m-audio 1010lt. As soon as I switched pre-amps to one of my VTB-1s it was gone. DPS II has a three prong plug, VTB-1 has a wall-wart PS. The only thing I added to my studio in the last month or two was/is a Lexicon MX200 again a wal wart power supply, connected digital to it from the 1010lt, and analog from it to the 1010lt via TS to RCA gepco snake. The radio Station was very faint. Oh and I had a shiny box ribbon plug'd into the DPS II when we heard the radio station. I have 50-65 foot gepco snakes between the mics and preamps, and on the mic end I had a 20ft canare quad mic cable. I haven't been able to do any more trouble shooting with this yet, but where the heck do I start??? :confused: :confused: :confused:
 
I worked in some studios in NYC where you'd occasionally get the conversations of taxi cab drivers on their CB radios coming over the NS-10M's. Didn't happen very often, but it was always good for a laugh.

Unless you can reproduce those AM radio transmissions while you do your troubleshooting, figuring out the source of the problem is going to remain elusive. If it only happens every now and then, I wouldn't worry about it. Just part of the fun, and the ghost in the machine.
 
One thing i can think of, radio frequencies generally have different wavelengths for different frequencies (that should be obvious). An antenna will pick up a given frequency best when it is of a length proportionate to the wavelength of the radio signal. If it is the cable that is acting like the antenna, try switching for a different length cable. If it were the power supply, try plugging into a difference outlet or via extension cord some something, you might be able to de-tune your "antenna"

Daav
 
If one of your Ballanced Mic cable has a Loose connection and suddenly becomes unballanced the Loose wire will act as an antenna and if the Cable is really long it will Pick up all manners of interferance, This is why you are not supposed to use Long cables with unballanced connections....

This would Probably explain the Problem as a Loose connection in a Cable would be Intermitant so it would Come and go....

Cheers
 
daav said:
One thing i can think of, radio frequencies generally have different wavelengths for different frequencies (that should be obvious). An antenna will pick up a given frequency best when it is of a length proportionate to the wavelength of the radio signal. If it is the cable that is acting like the antenna, try switching for a different length cable. If it were the power supply, try plugging into a difference outlet or via extension cord some something, you might be able to de-tune your "antenna"
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It probably isn't the mic cable unless one side of the transformer is grounded for some reason. Of course, if Shinybox took Lundahl's alternate wiring config as-is, it's wrong, and one side of the transformer -is- grounded, which means you have an unbalanced mic cable. I'm not sure how to check other than to crack it and see how they wired the transformer. My guess is that it isn't, though.

Try unplugging gear one piece at a time. Start with all the two prong devices, since they are the most likely candidates. My guess is that the DPS-II is getting hum dumped into it by some other device that isn't grounded very well.
 
Definitely RFI... could be from anything... In severe cases you can actually pick up this interference on a passive monitor that has nothing connected but a long stretch of speaker wire... (induced voltage on the speaker wire is enough to drive the cone).

AM wavelength is measured in hundreds of feet and antennas to recieve this signal are designed to resonate lengths... (1/2 wave, 1/4 wave, etc). It could be that you have a cable (or cables) that is (are) poorly grounded... that happen to be cut to one of these lengths.

The length of wire act like a dipole antenna... Dipole antennas are extremely directional... If the length of wire is pointed directly at the signal source, the source will be nearly completely nulled. so you may want to experiment with 1. various length audio cables... 2. moving the direction of your cable runs.

The bad news is... your electrical wiring is most often the culprit (long lengths of wire, running in vary directions around the structure). There's even a good chance that a faulty insolator on a utility pole outside your house has created a perfect AM antenna. The only way to elliminate this RFI source is generally with power transformers and/or choke coils. Ground lifts rarely work since the interference is induced directly onto the conductor, not the ground
 
BTW, its back, probably never left, though. I tired an extra 60-70 feet of mic cable on the connections down stairs, this time using regular brand new SM57s, still this AM station, its AM1190, out of Madison, WI I am in Sun Prairie, WI. Get it on the DPSII, but not my VTB-1s. I did try a cheater plug on the DPS, I don't think it made it any better or worse. House hold wiring was mostly redone by my uncle 5 years ago or so, everything passed his inspection then (he does it for a living, you should see how neat and tiddy my box is and all the runs that he redid)....no power poles in this neighborhood everything is underground, and our transformer is what maybe 30-40 feet outside from my rack (of course placement of the transformer only matters if it is airborn). I used Voxengo's VST SPAN audio analyzer, and you can see the 15-20dB range in peaks that you can hear of the radio station. That is peak to base line noise with no one talking or music playing to max peaks in music. Its mostly in the 2-3KHz range.
 
I used to have a fender dual showman tube head that sometimes radio signals could be heard on.
 
SRR said:
BTW, its back, probably never left, though. I tired an extra 60-70 feet of mic cable on the connections down stairs, this time using regular brand new SM57s, still this AM station, its AM1190, out of Madison, WI I am in Sun Prairie, WI. Get it on the DPSII, but not my VTB-1s. I did try a cheater plug on the DPS, I don't think it made it any better or worse.
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Are you going analog or digital out of the DPSII?

On another note, does this only occur with long mic cable runs? Because that sounds just like what I've gotten when I chain incorrectly wired cables. Make sure that every XLR connector has a jumper wire between the ground pin and the u-shaped grounding tab for the connector housing ground.

That jumper is often left out when making cables because it can cause problems between two pieces of powered gear, but when there's a microphone on the other end of the cable, it is more important, and when you chain multiple cables together, it is mandatory. Otherwise, the outer jacket of the connector turns into a giant antenna.

While you're at it, if the metal jacket doesn't screw on, make sure the set screw that holds it in place is making electrical contact with the jacket. That's another common point of failure.
 
Are you going analog or digital out of the DPSII?
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Digital, but I did try analog tonight and same thing.

On another note, does this only occur with long mic cable runs?
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My tracking rooms are downstairs, control room with pres are upstairs, gepco snakes wired thru the wall directly to the pres, and normally just one mic cable is attached to the snake downstairs.
 
Muhah!

Before our guitarists got their own amps, they played through a mixer/amp into a pair of PA cabinets at our rehealsalplace. Always when they stopped playing we could clearly hear some radiostation through the speakers, even with earplugs on.
It was a bloody laugh 'cause we're playing metal, and between songs some female character is telling childrens stories. :D
 
MOFO Pro said:
The only way to elliminate this RFI source is generally with power transformers and/or choke coils.
Click to expand...
Is that the same as wrapping the power cord through a ferrite ring?
 
Don't overlook the typical monitor or connector cable crossing a power or extension cord to form an antenna.

:)
 
Does anyone know about the mackie designed RF filter that you can build into a XLR male-female connector? Apperently some of the early makcie boards had problems with picking up radio stations, and there is a simple circuit that you can build into a connector....I was suggested this by a very good engineer, was told it was on mackie's site but hmmmm, they don't have a search box from what I can see....
 
Ok this circuit from the mackie people uses two choke coils and two caps, anyone heard of this? I just need the digikey part numbers and layout and I am there. As the guy who told me about used it 6 months ago in a church that was picking up AM1150 or something close to that, they had to make one for each mic line.
 
Was given the circuit design, digikey part numbers: DN2576-ND COIL 220.UH MOLDED UNSHIELDED and 399-2049-ND CAP .015UF 50V 10% CER RADIAL

Was told that the .015uF caps are just fine instead of the .01uF that are specified in mackies design.

RFfilter.jpg


Then I am going to put them in these: http://www.fullcompass.com/product/263291.html
 
Correct me if I'm wrong but isn't the Furman power conditioners suppose to eliminate things like that?
 
Not if the RF is getting in on the mic lines, they can correct some power line interference even then don't expect huge differences. And if its getting in the power lines to the preamps, the engineer at the station said it was most likely on the DC line out of the wall warts, well the furman would come before the wall warts, not after, and that is where you need the filtering.

In my neighborhood the AM strength of 1190 is half a watt per meter, so like the engineer pointed out, it's like getting one watt of AM directly picked up by the DC power line between the wart and the preamp.

But because I am getting the interference on my ART DPSII (has a regular three prong AC cord) with nothing plugged into it besides a mic and a pair of headphones connected to the line out (thats the test I did this morning), its probably entering on the mic lines.
 
Hay found a fix, Anyways was playing around just before 1190AM went off the air tonight, so around 6:30pm give or take. I had a Ribbon Mic plugged into my AEA TRP http://www.wesdooley.com/aea/TRP.html and nothing plugged into my ART DPSII and all was fine no 1190 thru my setup. Well I then crank the gains most of the way on the DPSII and TRP, and go downstairs where I have a headphone amp setup, pluged some headphones in and went to testing various configs. I got 1190 just by plugging in a mic cable into one of the DPSII snake channels, ok, so I change mic cables same thing 1190 still there. I then coil that cable and put it aside while listening to 1190 on the headphones, I then plug a mic cable with a SM58 into the snake that goes to the other channel on the DPSII, 1190 comes in stronger. I then coil the, well more bunch up that cable and throw it on the other cable that was coiled and 1190 decreases in strength thru the headphones, bring the cables apart; a stronger 1190, bunched together less 1190 go figure.

So I leave them apart to do some more fiddling. When I grabbed the connectors where that the mic cables and snakes were making contact together I could make 1190 stronger by grabbing a hold of them. Then by accident I moved the bundle of conectors of snake 1 where the overall shield drain wire of snake one was hanging out and the shield drain wire of snake two was hanging out, the two made contact, after that happened 1190 decreased by 95% (yes I have two snakes run down there, two 8 channel runs, wired for a total of 10 mic lines up and 6 returns down, snakes are gepco all with individual shields, then also a overall shield with a drain wire). So I twisted the drain wires of the two snakes together, and I couldn't really hear 1190 anymore. Faulty ground guys, on one or both of the mic lines that go to the DPSII???? Something else???

Of course 1190 could return with a different config, but for now, tonight, it was gone with the drain wires twisted together.
 
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