Scott,
I'll back your judgement on RF interference. As soon as you feed two
mic leads into one cable you are liable to set up a dipole with the
shielding let alone the conductors which will then conduct down the
star quad very effectively whatever the grounding arrangenets.
Two-pair cable won't pass on RF so well as it should be random twist
like digital cable. If it hits resonance, you have high level RF
straight into your preamps and you don't need dry joints to demod it.
The twist in any cable normally balances this out except when close to
a small source like a transformer. In the worst case twin screened
cable can act like a single turn on the magnetic source in series with
the mic circuit. Star quad is specifically designed to be symmetrical
to minimise magnetic interference as from power cables as opposed to
capacitative or RF pickup. Mains level is about +43dB (50db here) and
mic noise level is about -100dB, so screened balanced twin does a
marvellous job. BTW did you know that ordinary house wiring vibrates
at line frequency?
I once had dire problems filming a drama near the 200 KHz LW
transmitter at Droitwich. The problem there was a 100 metre run on
lapped screen cable which resonated into my Nagra. There was no better
field recorder than a Nagra, but even that couldn't cope with what
could have been volts of RF. My boomswinger had to shift his short
cable end till I got a null and then everyone had to stay in their
places for each take.
I think it was the Jimmy Young Show - for older UK listers. :-)
David
David Brinicombe
North Devon, UK
Cogito cogito ergo cogito sum - Ambrose Bierce
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