Larcan FM-250, Technical Manual

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FM-250 FM BROADCASTING EXCITER
Issue Date: 21 Jan 2003
The power supply module contains the smoothing capacitors for the ‘off board’ 230V 50Hz a/c
mains transformer/bridge rectifier combination. This +52V nominal smoothed supply is then
distributed to a choke/capacitor filter at the module. This type of arrangement eliminates all
ripple and therefor any AM products on the transmitter, even when the a/c input voltage is
extremely low. The +48V (nominal) external battery supply is combined off the module with the
smoothed supply via isolating diodes. The various voltages are then distributed to the other
modules.
Auxiliary supplies are generated for use in the RF PA regulator stage and Modules.
e) DISPLAY MODULE (980509)
The display module provides the Local user functions and alarm indications at the Exciter front
panel. The display has three functional meters, which allow instant viewing of multiple functions.
1) Multimeter: Provides push button selectable functions for Forward power, Reflected
power, PA current and Heatsink temperature.
2) ALC meter: Dedicated meter for instant viewing of ALC voltage and alarm.
3) MPX VU meter: Active peak detection meters for Left and Right channels, derived from
built in Stereo decoder. This provides instant viewing of Transmitter deviation from Left and
Right channels. The Stereo pilot indication is also provided with the meter.
Alarm indications are provided by Front panel LED’s, enabling instant viewing of transmitter
functions. Front panel adjustments are available for control of RF Output power and Deviation
level.
Connection for the optional RS485 Module is provided on the Display, enabling remote viewing
of Meter functions
.
f) STEREO CODER MODULE (980512) (optional)
This optional module allows the user to facilitate a very high quality stereo signal on board the
Exciter and provides all the necessary functions such as Pre emphasis switching, Mono- Stereo
switching with the added advantage of a built in Audio Limiter. The module accepts Left and
Right audio inputs (600 ohms balanced) and after Limiting and filtering is converted into the
Stereo multiplex format via a new digital stereo multiplexer. A 100kHz Linear phase filter is
used at the output with comprehensive phase adjustment to obtain absolute transparency.
A 19kHz Pilot signal output is provided for supplementary signal use.
g) BACK PANEL CONNECTIONS
The 110V 60Hz a/c power input is connected via an IEC connector whilst the +24 dc input is
connected via Binding terminals. Back panel Fuses are provided for maximum protection.
Standard telemetry output is provided via a 25 pin D connector, while the Remote frequency
control has a 15 pin D connector.