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Issue 3
However, if cable runs in excess of 100 metres are encountered or amplifier inputs are
required to be wired in parallel, it is advisable to select the line level output and use
amplifiers with line inputs. Using this higher level ensures that any unwanted interference
signals induced on the cable are of a low level compared to the speech signal.
If the amplifier only has balanced microphone inputs, it is possible to convert them to line
level using three resistors forming an attenuator as shown in Fig 1 below.
Fig 1
3.
Limiter
Selecting the limiter will ensure that the signal level remains fairly constant irrespective of
input level changes. Using it will prevent system overload when different personnel use the
microphone or speak too close to the microphone.
Note: Sensitivity increases by 12dB when limiter is selected.
BDM304M/308M/316M
The BDM304M, BDM308M and BDM316M have the same features as the BDM304/308/316
but have a factory fitted surveillance option to allow for monitoring of the microphone capsule
and control lines.
The surveillance frequency is factory set to either 20KHz or 1.5KHz (Default 20KHz).
The output surveillance level can be adjusted by VR1 on the surveillance option, which is
located on the rear panel inside the microphone.
Note : ‘Zone Busy’ indication is not operational on BDM304/308M/316M
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Line
level
input
level
Mic
output