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Issue 3
BDM 204
The BDM 204 dynamic microphone is designed to be used with our MITRE, ADEPT and VIGIL amplifiers.
It has the facilities to page up to four zones, either through selection, or all at once.
To Page Specific Selected Zones
1.
Select zones needed. An LED will illuminate indicating selected zone.
2.
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.
3.
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.
To Page All Zones Simultaneously
1.
Press ‘ALL’. NO ZONE LED WILL ILLUMINATE.
2.
The ‘Speak Now’ LED will illuminate as soon as the system is ready for 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.
3.
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. 3). 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 this
diagram.
1 k
1 k
22
Line
level
input
level
Mic
output
