Larcan FM-250, Technical Manual

Page: 22 / 86

FM-250 FM BROADCASTING EXCITER
Issue Date: 21 Jan 2003
OPERATING INFORMATION
FRONT PANEL
1. POWER ON/OFF SWITCH
The front panel On/Off switch connects the External A/C and D/C supplies to the equipment.
2. POWER ADJUST CONTROL
This single turn potentiometer is used to set the RF output power via the internal ALC
Circuit. Fully anti-clockwise gives minimum power (
≤
25W) while clockwise gives
Maximum power (
≥
250W).
3. DEVIATION ADJUST
This single turn potentiometer is used to fine trim the Transmitter final deviation level.
The standard variation is
±
1.5dB (other on request). This controls the total deviation
Level.
Note: When the stereo coder option is installed, the built in Limiter controls the maximum
Deviation level of the Left and Right program inputs and adjustment of this level is done
Internally, to customers requested level.
4. MULTIMETER
The Multimeter comprises a linear scale, 20 led (green) custom bar display. The meter
has a push button selector with individual LED's (yellow) for indicating the four selectable
Functions.
•
Temperature: RF PA Heatsink temperature with 100
°
C f.s.d.
•
RF PA Current: RF final stage current with 10A f.s.d.
•
RF Forward power: RF Output power with 320W f.s.d.
•
RF Reflected power: RF Output Reflected power with 32W f.s.d.
5. ALC METER
This dedicated 10 led (9 green and 1 red) bar display provides instant information on the
ALC loop control function and voltage. The meter indicates the dc control voltage at the
Gate of the final RF Mosfet stage and as such gives the user instant feedback on the status
of the ALC loop.
The meter scale is -5V to +4V (1volt per led) with the +4V led (red) indicating ALC ‘out
of range’.
6. VU METERS
This dedicated stereo meter is used to indicate the dynamic peak deviation of the Left
and Right channels. This provides the user with instant visual information on the status of
the system modulation.
The meters operate to the DIN 45406 specification with precision Full wave peak