Larcan DTT250M, General Description Manual

Page: 29 / 35

CONTENTS
C
ONTROL AND
M
ETERING
P
ANEL
...........................................................................................................................1
T
RANSMITTER
C
ONTROL
C
IRCUIT BOARD
A
SSEMBLY
...........................................................................................1
Control and Metering Panel
40D1985G1
Transmitter control and monitoring is performed by the Control and Metering Panel. This 19" wide, 3 unit (5
3
")
panel serves primarily as a mechanical mounting for the transmitter's control switches, status indicator lights,
and a multifunction meter. It also is the mounting for the control circuit board described below, and for an
output metering circuit board.
The transmitter control panel features as seen from the front, are:
•
A panel meter calibrated 0 ‐ 125 percent, and a 0 ‐ 100 linear scale;
•
The meter input selector switch for forward and reflected power, IPA output level, and AGC voltage;
•
Pushbuttons for ON, OFF, REMOTE/LOCAL, AGC ON/OFF, TX RESET;
•
A screwdriver adjusted potentiometer for the desired AGC level, hence transmitter output power;
•
Five LEDs providing indications (from left to right) when lighted:
o
EXT 1 interlock is closed,
o
the output amplifier TEMP thermostat is cool,
o
EXT 2 interlock is closed.
o
VSWR L/O when lighted means three major VSWR events have occurred during a short time and
the transmitter is now off the air, and
o
VSWR C/B lights up during a VSWR event that is sufficient to cause the transmitter power output
to decrease, or even to momentarily turn off the transmitter.
The transmitter is provided with a VSWR cutback function that either reduces its power output to save it from
harm in the event of gradual occurrences such as antenna ice build ‐ up, or momentarily takes it off the air from
random events.
Three VSWR events occurring rapidly in a short time will cause the VSWR Lockout mode to turn the transmitter
off until it is reset. Random VSWR events normally do not cause lockout unless the reflection is sustained,
causing repeated momentary tripping and ultimate lockout. Antenna or line damage occasionally can be a factor,
but usually ice accumulation on the antenna causes sustained high VSWR.
Transmitter Control Circuit board Assembly
30C1829G1
See Figure 1 and Figure 2.
There are seven connectors on the Control circuit board. These connectors perform the following functions:
•
J1 interconnects with J3 of the Metering board via a 34 ‐ wire ribbon cable.
•
J2 connects elsewhere in the transmitter, such as the exciter and the PA, and to the meter.
•
J3 connects to the external interlocks, and any special local controls for TX off and on functions.
•
J4 interconnects with J4 of the Metering board for the AGC potentiometer and switch wiring.
•
J5 is a 15 ‐ contact D ‐ shell connector provided for user remote control system.
PUB96-32 Rev 2 August 29, 2005 32-1 TX Control Panel 40D1985G1