INS-42037-1: FMC88108-6
User’s Manual
Asia Pacific | EMEA | Americas
17
7.2 Transmit Function
The FMC88108-6 Repeater Translator is primarily used for receiving (normally from a single antenna) and then re-
broadcasting up to six separate VHF FM carriers (individually adjustable via R97 on each translator module)
The receive and transmit frequencies are selected via the DIP switches SW1 (Receive) and SW2 (Transmit) on each
translator module. The receiver and transmitter will normally be set to the same operating frequency, but alternative
frequencies can be used if so required by the end user. Frequency programming tables are provided in section 5 of this
manual for this purpose. Green LED indicators D8 and D9 are provided on each translator module for indication of Rx and Tx
synthesizer lock.
Each translator module has a potentiometer R97 (RF level adjust) to set the RF output level. These levels are normally set
using a spectrum analyser, displaying all carriers simultaneously.
7.3 Receive Function
Each translator module is equipped with a tunable RF channel filter which must be fine tuned to the desired frequency. Coarse
tuning is done automatically via varactor diodes and fine tuning is done by simply adjusting inductors L1 and L2. These will
normally be set at the factory but can also be adjusted by the end user. To tune the filter, monitor the DC voltage at IC7, pin
13 with a digital Volt meter and adjust L1 and L2 to achieve the maximum positive voltage. This can be done either with an off-
air signal or with an RF signal generator.
No other adjustments are normally required on the receiver section as these will be preset at the factory.
7.4 Break In Facility (BIF)
When an emergency audio broadcast is required to all six FM channels, the audio source is input to one of the isolated BIF
inputs (BNC’s) on the rear panel. No pre-emphasis is required for this purpose as it is already tailored for speech within the
FMC88108-6. The BIF audio feed can be activated by grounding pin 1 (100mA sink) on the telemetry D9 connector. (Ground
is available on pins 2 and 3)
The BIF deviation levels for all carriers can be adjusted via a single potentiometer R13 on the display/distribution module. This
is normally set to provide ± 68 kHz deviation with a 500Hz tone.
A summary alarm is also available on the telemetry connector on pins 6 and 7. This output contact is voltage free and can be
set for s/c or o/c contact via LK1 (on the display/distribution module)
The summary alarm will be activated should any of the receivers lose signal strength (below 100µV) or any of the transmitters
have loss of output level (below -15dBm)
Green LED indicators are provided on the front panel to allow visual indication of Rx and Tx status. LEDs will be illuminated
when conditions are normal. If a translator module is removed the LEDs for that particular module will be off.
NOTE: if the end user decides to only use a lesser number of modules than the six fitted, then the jumper links (for the
summary alarm) for those particular modules should be removed, otherwise the summary alarm will be activated.
These links are situated on the front panel display/distribution PCB:
Module 1………………………….LK2 and LK3
Module 2………………………….LK4 and LK5
Module 3………………………….LK6 and LK7
Module 4………………………….LK8 and LK9
Module 5………………………….LK10 and LK11
Module 6………………………….LK12 and LK12
The unused modules should be disconnected at SK3 on the display/distribution PCB so that their Tx carrier is removed.
