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Re: [ARSCLIST] RF problems - used to be - - Effect of vibrations on audio tape

Mu-metal is a very effective magnetic shield against near-field emissions
from motors and high current-carrying conductors. Copper is an excellent
shield for far-field radio frequency emissions where the radiating source is
more than one wavelength from your equipment. Copper is more available and
much less expensive.

Metal screening, such as some fencing materials, can also be an effective RF
shielding material. Be sure that conductor spacing is less than a tenth of a
wavelength, and that each wire is electrically connected to its neighbors.

Media Sciences, Inc.

> -----Original Message-----
> From: Association for Recorded Sound Discussion List
> [mailto:ARSCLIST@xxxxxxx] On Behalf Of James Lindner
> Sent: Friday, October 27, 2006 7:29 PM
> To: ARSCLIST@xxxxxxxxxxxxxxxx
> Subject: [ARSCLIST] RF problems - used to be - - Effect of vibrations on
> audio tape
> Mu-metal is a better choice then copper, but if you go all the way you
> basically have to do the same things you need to do for Tempest emissions
> -
> and you probably don't want to go that far.... but having said that and
> having built several facilities in NY over the years, if the RF source is
> really that strong, you may find that a hugely oversized ground that is
> used
> for ALL the equipment and shielded cable is adequate enough. In the
> facility
> that I have now - we are in line of sight with the empire state building
> and
> only about 4 cross town blocks away - plenty close for plenty of RF. For
> grounding I have ignored the standard electrical system ground and opted
> for
> a huge copper plate that is bolted into the steel superstructure of the
> building. It works.
> Radar is WAY up there with very short wavelengths and harmonics go up not
> down. The inverse square law applies so the power falls off very quickly
> relative to the distance from the source and you are modulating through
> the
> air if it is the kind of RF that you are suspecting.
> I have a couple of suggestions. You may need to hire an outside company to
> do this - but first of all you need to have an RF survey done of your
> site.
> This is not difficult to have done - basically it is a field strength
> meter
> that sweeps different frequencies and is a good idea to do if you are
> putting up any major facility.
> I would also get a power line survey done - and look at the power on a
> scope
> and look for harmonics and switching interference. See if you have a clean
> sine wave - and for fun buy a UPS and move the source of the noise to the
> UPS and see if anything happens. You may find that the noise will travel
> with the power, and it may disappear when you use the UPS because it is
> back
> RF modulation on the line. IF that does not work - time the peaks and
> troths
> of the noise and see precisely what the time is - and if it changes at
> different times of the day, and over the week end also.
> Unless you are right near the radar - I doubt that this is the culprit -
> unless it is a military radar and you are line of sight and it is close -
> and if it is.... frankly - - - I would rather work in a different
> building.
> Radar that strong isn't good for people either.
> Jim Lindner
> . Email: jim@xxxxxxxxxxxxxxxxx
> . Media Matters LLC.
> . Note New Address: 450 West 31st Street 4th FL
> New York, N.Y. 10018
> . eFax (646) 349-4475
> . Mobile: (917) 945-2662
> . www.media-matters.net
> Media Matters LLC. is a technical consultancy specializing in archival
> audio
> and video material. We provide advice, analysis, and products to media
> archives that apply the beneficial advances in technology to collection
> management.
> -----Original Message-----
> From: Association for Recorded Sound Discussion List
> [mailto:ARSCLIST@xxxxxxx] On Behalf Of Mike Richter
> Sent: Friday, October 27, 2006 6:03 PM
> To: ARSCLIST@xxxxxxxxxxxxxxxx
> Subject: Re: [ARSCLIST] Effect of vibrations on audio tape
> David Seubert wrote:
> > Jim Wheeler once suggested that we line the studio with that copper
> > sheeting with holes in it like the door of a microwave oven. We never
> > did this, but I'm open to suggestions.
> A Faraday shield is quite effective, but quite costly. It requires more
> than lining the studio, but there are companies in the business who can
> deal with collateral problems such as those imposed by windows and doors.
> To find such a resource, check with the facilities people at a
> convenient DoD installation near you. Let me note that I've worked in
> such a situation and found it depressing.
> Mike
> --
> mrichter@xxxxxxx
> http://www.mrichter.com/

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