Neumann.Berlin Condenser Microphones Manual del propietario

Neumann-Information

183 August 1983

Some informations on RF-interferences in the Studio

Neumann condenser microphones are protected through various

means very effectively against RF interferences so that they

may be used also in those cases where other microphones due

to heavy RF radiation do not perform satisfactorily. Some of

our past years experiences pertaining to this Problem have

been collected here for the purpose of helping to identify

this type of interference and to simplify its removal.

1. RF frequencies always enter through the microphone cable

and never through the capsule housing.

2. All microphone cable couplings must be arranged so that

the cable shield is connected to the connector Shell at

both ends of the cable. It is not sufficient to connect

theshield only through the relevant plug Pins. The

shield must be soldered to the connector Shell. In case

of heavy RF rad'iation it is not sufficient to only clamp

the shield by means of a screw. All connecting cables

supplied by Neumann comply with these requirements. Very

often when our customers prepare their own cables the be-

fore mentioned interference Problems appear, because the

prerequisites are not adhered to during cable assembly.

3. Microphone cables with a woven shield have a remarkably

lower degree of covering an area than such cables using

counterrotating double reusen shielding. For this reason

cables with reusen shielding are remarkably better pro-

tecting against RF interference. Neumann microphone

cables are using this counterrotating double reusen

shielding. Cables which are shielded only through conduc-

tive plastic material are not RF-proof.

4. Only demodulated high frequencies appear as interference.

Semiconducter circuits, especially the gates of the

fieldeffect transistors, may therefore not have any

capacitive coupling to RF frequency Signals.

5. If it is not sure whether the demodulation happens in the

microphone or in other equipment to which the microphone

is connected, it is recommended to test this by means of

a 200 Ohms equivalent resistor built into a plug which is

connected instead of the microphone, or with a dynamic

microphone.

GN1

CHARLOTTENSTRASSE 3 . D-l000 BERLIN 61 . POSTFACH 610469 . TELEGRAMM: NEUMANNACUSTIC

TELEFON: (030) 25993-0 . TELEFAX: (030) 25993-106 . TELEX: 164595 NEUAK D Printed in Germany

6. Only amplitude modulated RF leads to interference.

Inter-

ferences caused by FM-transmitters are not known to

us.

7. For interference caused by Standard broadcast and short

wave transmitters the audio program becomes audible.

With TV-transmitters the frame frequency (50 Hz or 60 Hz)

is perceived and is easily confused whith AC power line

hum. If the interference level fluctuates strongly with

movement of the microphone or cable then a TV-transmitter

is the probable Source of the interference.

8. Because TV-transmitter antennas are usually placed at

high elevations and most often radiate with horizontal

polarization, antenna masts located in the immediate

proximity often

not present the danger that those

located further away

do.

9. Older microphones of the type U 87 tan, if necessary, be

modified to up to date circuitry and thereby become vir-

tually as RF-prooved as the other microphones. This

applies mainly for the exchange of the transformer 09013

against the type 90415 (with electrostatic shield win-

ding, which is Standard beginning with circuit Status 19)

and the installation of the RF-rejection filter in the

base plate of the microphone (Choke 1 and 2 with C 16 and

C 17, which is Standard beginning with circuit Status

17).

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