Random thoughts about ground, cables and RF.
Back in the early '70s Fred Schiller, the chief of maintenance at WHA
told me, "Follow the rules about grounding, and when that doesn't
work, start lifting and adding grounds till it does. I think of Fred
every time I go into a studio.
The biggest problem that I've found in radio stations is installers
that thought punch blocks were "ends", and that therefore the drain
wires didn't continue through. Lots of lovely antennas to pick up RF.
In the '80s, I was trying to record in a church across the street
from a 50KW FM on a short tower. Tried everything. What worked was
star quad mic cable. PROCO worked as well as Canare. I recall also
having to get creative with grounding as well, but what I did I don't
When I worked for API, we frequently had problems with RF from the
defense installation down the block. It manifested itself as noise.
Saul Walker told me, just increase the gauge of the ground bus.
In a house, I'd drive more ground rods. We used to salt the earth
around ground rods at transmitter sites. On top of Mt. Mansfield, we
kept losing the submersible pump, 300' down the well to lightning.
It was the best ground on the mountain. Granite is not the best
conductor known to man.
Diodes make great RF detectors, but a diode isn't always an
electronic devices. On top of Mt Mansfield, we had problems with our
107.9 mixing with FAA transmitters at the site, and interfering with
the frequency that the bombers at Plattsburgh Air Force base used for
landing directions. It seems that they didn't like to listen to
Robert J Lurtsema, while landing . Harmonics were involved along
with sum and difference mixing. We searched for weeks, and finally
found the "diode". It was a rusty bolt on our tower. I've also seen
poor bonding between chassis panels in an audio mixer act as "diodes".
>When I started to work in the music studio of the National Film Board of
>Canada in 1979, we had a mic cupboard full of good stuff. There were a
>number of brand new AKG-414s. But I was told that I couldn't use them
>because of RF problems, and the NFB was actually considering selling the
>mics since they were unusable. I got our maintenance department to make a
>"special" cable that tied pin 1 to the shell of the connector. Bingo, the
>mics were clean of RF and I scored big points with my new boss. In the 20
>years I was there, I never found the RF source even though the studio was
>surrounded with chicken wire supposedly well grounded.
>2014-06-21 16:00 GMT-04:00 Richard L. Hess <[log in to unmask]>:
>> On 2014-06-21 3:54 PM, Paul Stamler wrote:
>>> Remarkably, I heard similar stories from the engineers at the Ravinia
>>> Festival about Neumann mics. They also went to C451s and some Shure
>>> SM81s, and the problem was solved. The SM81s and C451s had far fewer
>>> problems with humidity than the KM 84s.
>> That is interesting as Neumann has published on the subject and also
>> developed their double wound (in opposing directions) spiral-shielded mic
>> cable (called double Reussen shielding, I believe). Here, the cable is
>> called "Gotham" cable after Gotham Audio, for a long time the sole importer
>> of Neumann mics into the USA. I had thought it was Neumann cable, but
>> perhaps it was Gotham. It is still available. I still have a pair of 50'
>> and some 10' cables that I bought in the 1970s and they are still
>> performing well (though I don't use them that often).
>> Although this was not the article I recall, it seems interesting and talks
>> about Pin 1 and Pin 0 (the shell) and I do recall some of that discussion
>> from the earlier paper.
>> Part of what they published (IIRC) was relating to the shield ground and
>> pin one. I do not recall exactly what they recommended, but I do think that
> > it was an early indicator of a pin one problem.
>> I have yet to have an RF problem with my KMS-105 or TLM-103, but neither
>> of those were hung in the church, used on the floor.
>> In fact, the only mics that ever gave me a problem here in Aurora were the
>> ATM10a's, which, also, coincidentally were the least expensive condenser
>> mics I ever bought.
>> To fill out the list, although none hung in the church, all were used
>> there without any RFI issues: Rode NT5, Rode S1, Sennheiser MKH416T with
>> homemade P48-T12 adapters, and dynamic Shure PG58, SM58, and EV ND767.
>> Richard L. Hess email: [log in to unmask]
>> Aurora, Ontario, Canada 647 479 2800
>> Quality tape transfers -- even from hard-to-play tapes.