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

[James Lindner <jim@xxxxxxxxxxxxxxxxx>]

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
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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/