Multi Channel Transmitter (MCTX) - Installation,
Commissioning and Maintenance
Page 10 of 16
If you wish to change the frequency of an individual channel then you will need to adjust the
frequency select switch. Rotate the small HEX switch (SW 1 for odd channels or SW2for even
channels) to the required channel. This switch is labelled in HEX so you will need to convert the
required channel number to HEX ( channel 1 = 0, channel 2 = 1, etc to channel 16 = F) before
setting it. You should not need to set or adjust any other internal control.
The audio input signal should be adjusted so that the bargraph indicates to the yellow LED with
occasional peaks into the red LEDs. Signals which are too high will be limited to a maximum of
+6 dBu to avoid over modulation. The limiter is designed so that signals less than +6 dBu will
not be affected but any over the limit will sound distorted.
Emergency message module EM1 and EM2
The emergency message volume (EM2) is
preset at the factory and should not
require any adjustment. When activated
the signal will be indicated on the LED
bargraphs and it should not exceed 0dB
so that the transmitter is not over
modulated. Check the transmitter output
using a receiver and listen to see that the
audio signals are muted and the
emergency message is played.
The standard message is
“Attention please, attention please, this is an emergency. Please
leave the building calmly by the nearest exit. Do not use the lifts”
The microphone gain is set using the three preset resistors located on the front edge of the mic
card (EM 1). Turning the control clockwise will increase the gain. Do not set the input gain too
high as this will cause over modulation of the transmitter making the speech unintelligible. You
should also be aware that close speaking into a microphone will cause “pop” where the speaker’s
breath causes the diaphragm to have excessive movement and thus high signal levels will be fed
to the transmitter. Check the transmitter output using a receiver and listen to see that the audio
signals are muted and the microphone message is heard.
The mic inputs have priority switching to enable senior management to take control in case of
an emergency. All the mic inputs will override the emergency message. The order of priority is
for mic 2 to override mic1 while mic3 overrides mic2 and mic 1.