Radio Towers and recording non-audible sounds

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I have Avenson STO-2 mics and a Korg MR-1000 with Mogami Gold cables. This rig is nice and relatively immune to cell phone interference. The mics seem sensitive to high voltage, but otherwise problemless recording most of the time. I recorded at a football stadium down town within a couple blocks of a radio tower this weekend(San Antonio). And fortunately I brought headphones to monitor, as I was picking up the local radio station. I'm not sure if it was the mics, or the field recorder picking it up. Or just the headphones.

I lowered the mics about 2' and most of the signal went away. I tucked the field recorder under the aluminum bleachers and the rest seemed to go away. This chewed up a bit of time to fine tune, which I had planned on using to take pictures and shoot video. Nothing too critical this time out. But I'd hate to encounter this issue again when it really matters. Obviously different mics would help, but I'm not quite sure why I had to move the position of the field recorder to mitigate the interference.

Any tips for taking this possibility out of my equation?

1) different mics (although I don't think this would have completely fixed the issue in this case).

2) better shielding for the field recorder.

???

I've been toying with the ideal of putting my camcorder inside the shell of an old studio monitor to protect it from the heat of direct sunlight and possible rain. This would also make it so I could mount the field recorder inside the shell as well. The shell would also shade the LCD so it can be seen in sunlight conditions. Should I line the inside of the shell with a few layers of tin foil to mimic the bleachers in shielding the field recorder from this hazard? Or is that of little consequence. It certainly seems that I need to do something special, but what?
 
Shadow_7 said:
I recorded at a football stadium down town within a couple blocks of a radio tower this weekend(San Antonio).
Click to expand...

Radio tower emits hundreds of wats, and you will always have interference in it's vicinity, without proper shielding / grounding. Especially if the emission is AM.

Much also depends form the mic construction, such as Shure beta series should do better (I know that some of them have coils like humbucker design, so not so sensitive to noise, I don't remember exact models, so help please ... ).

you should search for equipment, that would qualify as field recording equipment, in my delay work (internet TV) i have come across of all kind of strange interferences, and have found that so pro tv equipment is much less suspectable to such problems. there for I use Rode NTG-2 for mics, haven't head any problem. other thing, a good cable, and correctly soldered one, often no connection is made to body of the mic, (it is the small extra connection in XLR cable). sometimes connecting it helps, sometimes the opposite. Not connecting it helps with ground loops trough earthed equipment, such as studio, and opposite in here only grounding element is the human holding the mic ;).

SAFETY FIRST TOUGH!!!!

You have to do experiments try different setups and find one that works. good luck!
 
Faraday Shield

Shadow_7 said:
I have Avenson STO-2 mics and a Korg MR-1000 with Mogami Gold cables. This rig is nice and relatively immune to cell phone interference. The mics seem sensitive to high voltage, but otherwise problemless recording most of the time. I recorded at a football stadium down town within a couple blocks of a radio tower this weekend(San Antonio). And fortunately I brought headphones to monitor, as I was picking up the local radio station. I'm not sure if it was the mics, or the field recorder picking it up. Or just the headphones.

I lowered the mics about 2' and most of the signal went away. I tucked the field recorder under the aluminum bleachers and the rest seemed to go away. This chewed up a bit of time to fine tune, which I had planned on using to take pictures and shoot video. Nothing too critical this time out. But I'd hate to encounter this issue again when it really matters. Obviously different mics would help, but I'm not quite sure why I had to move the position of the field recorder to mitigate the interference.

Any tips for taking this possibility out of my equation?

1) different mics (although I don't think this would have completely fixed the issue in this case).

2) better shielding for the field recorder.

???

I've been toying with the ideal of putting my camcorder inside the shell of an old studio monitor to protect it from the heat of direct sunlight and possible rain. This would also make it so I could mount the field recorder inside the shell as well. The shell would also shade the LCD so it can be seen in sunlight conditions. Should I line the inside of the shell with a few layers of tin foil to mimic the bleachers in shielding the field recorder from this hazard? Or is that of little consequence. It certainly seems that I need to do something special, but what?
Click to expand...

Hi,
I think making a shielded housing for your gear is a great idea. 15 years ago I lined the walls of my control room with aluminun foil. Then I covered it with thin plywood. I bonded a piece of #6 copper to the foil and then connected to a bank of ground rods. I recently reroofed my studio and before the shingles I layed down 36" aluminum flashing, I then bonded #6 copper to the flashing and connected to 2 ground rods. Since I have done this interference has been greatly reduced or illiminated, musicians wives cant interfere with cell phone calls all night long. I have a lot of alumium flashing left over if you need some.
VP:cool:
 
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You wouldn't happen to live anywhere near Austin Texas would you?

Being Texas I don't want anything externally metal. It's hot enough as it is. The little warning icon with a thermometer was lit on the LCD of the camcorder already. And it's only may. This is why I figure that the wood shell of an old studio monitor would be swell. The 8' speaker cone makes a good viewport for the camcorder. Shove a coffee or mixed nut can in there for added rain cover. Squarish so put a shelf or two above for the field recorder, maybe an external preamp too. Screw down a stereo bar to the top, put a boom arm to the side. The only thing I haven't figured out is attaching that to a tripod. But even if I end up having to hold it in place an entire concert, everything will be an arms reach away. Although battery swaps might be a bear.
 
Shadow_7 said:
You wouldn't happen to live anywhere near Austin Texas would you?

Being Texas I don't want anything externally metal. It's hot enough as it is. The little warning icon with a thermometer was lit on the LCD of the camcorder already. And it's only may. This is why I figure that the wood shell of an old studio monitor would be swell. The 8' speaker cone makes a good viewport for the camcorder. Shove a coffee or mixed nut can in there for added rain cover. Squarish so put a shelf or two above for the field recorder, maybe an external preamp too. Screw down a stereo bar to the top, put a boom arm to the side. The only thing I haven't figured out is attaching that to a tripod. But even if I end up having to hold it in place an entire concert, everything will be an arms reach away. Although battery swaps might be a bear.
Click to expand...

Why dont you just use a lunchbox with an ice pack...that might come in handy for some upskirt footage too.;)
 
Your title,
Shadow_7 said:
Radio Towers and recording non-audible sounds
Click to expand...
strikes me as funny.

We use our ears to monitor and listen to whatever we record- if you recorded "non-audible sounds," how would you ever know?

We may well be doing that all the time, and no one is the wiser...
 
darrin_h2000 said:
Why dont you just use a lunchbox with an ice pack...that might come in handy for some upskirt footage too.;)
Click to expand...

It'd have to be a lot of ice for these parts. It probably wouldn't survive the 1 hour drive to the site, much less the 3.5 hours of continuous record times I'm striving for. Right now I get about 2 hours 45 minutes of audio on battery power. And about 2 hours on the camcorder. Per set of batteries. Plus I don't plan on getting that close to people. And digital video doesn't do that well in low light yet. And you wouldn't get much useful stuff from the women in these parts. And the men don't wear skirts.
 
Faraday Cage

I never understood completely how a cage would work, but apparently it does, has to do with the size of the wavelengths I guess. I read about a Faraday cage before I grounded my control room with Reynolds Wrap. It would have been cheaper and easier with chicken wire or screen but I figured 100 % coverage would be best. Thanks for the reminder!
VP;)
 
Inverted?

:confused:I dont know how my reply appears before your reply?
 
Shadow_7 said:
Being Texas I don't want anything externally metal. It's hot enough as it is. The little warning icon with a thermometer was lit on the LCD of the camcorder already.
Click to expand...
A farady shield doesn't have to be solid, you could use a screen (or chicken wire) as long as it's conductive and grounded.
 
Technically, it doesn't have to be grounded, but in practice, yeah, it should be.

I would caution that the maximum size of gaps that you can tolerate is frequency-dependent. If you're just dealing with AM/FM, then chicken wire is fine. If you have to deal with leakage from a microwave tower, you'll need something with smaller holes.

Also, I see to recall (but can't confirm) that leakage from nearby powerful stations can occur through the ground if it is saturated (wet) via skin effect. Not positive about that, though.
 
Skin Effect

dgatwood said:
Technically, it doesn't have to be grounded, but in practice, yeah, it should be.

I would caution that the maximum size of gaps that you can tolerate is frequency-dependent. If you're just dealing with AM/FM, then chicken wire is fine. If you have to deal with leakage from a microwave tower, you'll need something with smaller holes.

Also, I see to recall (but can't confirm) that leakage from nearby powerful stations can occur through the ground if it is saturated (wet) via skin effect. Not positive about that, though.
Click to expand...

That is why I like to use solid aluminum, It gives maximum shielding. The skin effect is a fascinating phenomenom. I have worked as an electrician at cell sites and would be amazed at the hollow copper tubing used for the RF antenna cables. I suppose the skin effect still happens in audio too, of course the higher frequencies.:cool:
 
Hmmm. Tin foil locked in place with chicken wire, then staple gunned. In inventory and within my skill set too. I guess using a plastic storage bin instead of a wood shell might be out. I wonder if lowes carries the same wood amo box that Meyers up north carried. It's just about the right size and a whole lot cheaper. It doesn't have to be pretty, just functional. And mobile. One person, one trip. But do I put the camcorder and field recorder in the same enclosure. The camcorder seemed to be immune to the radio tower. But not to the wind noise. And it's audio sort of sucks in comparison. But not completely horrid.
 
The times that I've picked up radio stations, it has usually been caused by cables whose plugs had plastic backs that don't shield against outside noise and/or floating (ungrounded) metal backs that are even more fun.
 
I had some older Avensons that were suseptable to interference from cell phones. I called brad - he said he gets occaisional calls about things like this on his earlier mics. He can fix them. His service is outstanding. Let him know - I'm sure he can help.
 
Oh, man, I chuckle at the mental image of ANYTHING encased in chicken wire... except maybe chickens. Reminds me of the country-western bar scene in "Blues Brothers." (and I have played just that sort of club...)
 
the only time this ever effected me the signal ws coming from a fender dual showman blackface amp.
 
leddy said:
I had some older Avensons that were suseptable to interference from cell phones. I called brad - he said he gets occaisional calls about things like this on his earlier mics. He can fix them. His service is outstanding. Let him know - I'm sure he can help.
Click to expand...

Well it's immune to cell phone handshakes. Although I'm not sure of the age of these mics. SN's below 400. Electrical box on the back side of the trailer when the A/C is running, not so much. Although having three layers of fake fur over the mics to mitigate wind noise, seems to also mitigate some of that electrical interference.

I'm not sure why most of it went away when lowering the mics more towards eye level. I like keeping them elevated to mitigate the oohs and aahs of the audience versus the SPL level of the group in the distance. Plus anyone in proximity are a little more at ease when they're not in danger of swallowing the mics. Or poking an eye out.

Shielding the field recorder from direct line of sight seemed to mitigate the rest. I was sort of surprised that any of that helped. Initially I thought that I'd driven 100+ miles for naught. That'd id be left with just the video aspects from the camcorder. Which I was rather glad that I had added to my kit less than a month before. The neutrik plugs on the mogami's do seem to be mostly plastic ( or plastic looking ). Would wrapping just those in tin foil accomplish the same goal? Or painting in gold leaf if I wanted to be fancy. The main body of the Korg is AFAIK aluminum. Which is why I was surprised that the field recorder seemed to be contributing to the issue.

-----

In this instance non-audible sounds means sounds NOT heard if you put your ears in the same location as the mics. But are recorded and audible when monitoring through headphones. Although not always audible (until you get home) when the group is louder than the headphones can output at the monitoring location.
 
Neutrik make a special connector to help reject RF:

http://www.neutrik.com/us/en/audio/204_1603252336/EMC-XLR_Series_productlist.aspx

But still, even if there is a small gap in the shielding, you still have common-mode rejection of hopefully 70dB or better. Inside the Korg is a different problem; at that point you are reliant upon circuit design and shielding. I think a metal mesh box should help.

If the mics are susceptible to interference, that's a different problem. Some designs are more so than others. It probably wouldn't hurt to carry a pair of ENG-style omnis or instead something like a pair of Beyer M201s to save the day when required. Most quality dynamics use humbucking coils and are shielded as well.
 
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