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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
do
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).