MXD5U OPERATIONS AND MAINTENANCE
Turn OFF Amplifier.
VSWR Trip
With Amplifier OFF, install a short length of cable at the RF output, if one is not already there. Add an N-type Tee
connector on the output of the cable. Connect a 50R load on each of the two female connections on the Tee. This
results in a 10dB Return Loss for VSWR setup.
Ensure E8 is installed. Remove J8 temporarily to prevent cutback.
Turn on the Amplifier.
Monitor the Reflected Detect port on the Directional Coupler. Note a voltage in the range of 0.4 to 0.9V.
Remove RF input. Measure TP3 and set R54 (offset) for 0.02VDC.
Apply RF again. Set E6 to get TP3 between 4 and 8VDC.
Monitor TP4. Set R60 for 4.4V.
Install J8 and set R105 (cutback) clockwise to where VSWR condition (LED DS9) clears; Forward power is
between 25% and 40%.
Turn off Transmitter, Connect good load to RF Output again. Turn on Transmitter and check front panel sense
output. Rf Level should be 24-26dB down from the transmitter output level; about 12-14dBm.
Shut off Transmitter. Remove the jumper wire from the INT’K (External Interlock) terminal block at the rear panel.
Performance Checks
Total DC Current Consumption at 6W output: 3.3 to 4.0A.
Shoulder levels: 37dB WRT Barts Head at 6W output, full UHF band.
Restore EXT INTL’K at rear panel as required for end use.
2.3 R
EMOTE
C
ONTROLS AND THE
MXD5U
F
RONT
P
ANEL
ON/OFF
B
UTTON
The Front Panel ON/OFF button on the transmitter can function in two distinct modes which depends on the
position of jumper E5 on the 31C1897 control board located inside the transmitter chassis. E5 that can be placed
in either of two positions, one labeled ‘INT’ and the other position EXT.
When the jumper E5 is in position INT, then the transmitter will ignore any ON or OFF remote controls. This
remote controls can either come from the serial communication program or from the external remote control
connector on the rear of the transmitter chassis. Please note that only the ON and OFF remote controls are
disabled and the AGC raise/lower and Vswr reset commands will still be operational. In this mode the transmitter
can only be turned ON or OFF via the front panel button. This is mostly for maintenance purposes when the
technician is working on the transmitter and doesn’t want anyone to remotely turn it ON or OFF.
When jumper E5 is in the EXT position then remote controls are enabled, this is the normal factory setting as
shipped. Even when E5 is in the ‘EXT’ position, the front panel button will still shut the transmitter OFF if it is
placed in the OFF position but when the front panel button is pressed in then the remote ON/OFF controls are
enabled. The transmitter records the last known requested ON/OFF state from the remote control and will cause
the transmitter to enter into that state. If the operator last issued a remote OFF command then the remote state of
the transmitter would be OFF and if the operator last issued an ON command then the remote state of the
transmitter would be OFF. This is done to insure that when remote control is enabled and an AC power failure
occurs, then upon restoration of AC power the transmitter will return to the ON/OFF state is was in prior to the AC
power failure. This is necessary since the remote ON/OFF commands are momentary closures and are not
present all the time.
PUB09-03 Rev 0 April 16, 2009
09-03-5
MXD5U Operations and Maintenance
