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Issue 3
BDM 201
The BDM 201 dynamic microphone is designed to be used with our MITRE, ADEPT and VIGIL amplifiers.
To Operate
1.
Press ‘Speak’ and make the announcement. If a pre-announcement chime is being used, the
‘Speak Now’ delay function must be selected. The LED will illuminate after 2.5 seconds
indicating that the system is ready for the message.
2.
During the announcement the speech volume indicator will fluctuate. Try to keep the indication
constant without the yellow segment illuminating. Maintaining a constant level will aid intelligibility.
Additional Features
Several important functions are incorporated into the microphones and maybe selected as required. DIL
switches are accessed with a screwdriver through the base - refer to Figure 2.
1.
Speak Now Indicator
The ‘Speak Now’ LED will operate in two different modes.
* A)
Illuminates instantly when P.T.T. is pressed.
B)
Illumination delayed by 2.5 seconds to allow time for the chime to operate and finish. The delay circuit
is built into the microphone. This avoids having to feed a return back from the amplifier.
(The microphone is only live when the LED is illuminated).
2.
Output Level Option
The balanced audio output can be selected to either microphone * (2.5mV) or line level (250mV), switchable
by careful use of a small screwdriver or similar tool (See Fig. 4). Twin screened cable runs, up to 100 metres,
generally operate well at microphone levels. 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 Figure
1 below.
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.
Technical Specification
MICROPHONE
LINE
Nominal output level
2.5mV
250mV
Maximum output level limiter operating
7mV
700mV
Output impedance
47ohms
400ohms
Frequency Response
200Hz - 10KHz
Power Requirements
24V DC
26mA Standby
45mA Max
The cable is terminated to a 6 pin DIN plug. It is supplied with a BMS6 single gang socket box and
connections are made using the terminal block inside the box.
1 k
1 k
22
Line
level
input
level
Mic
output
