User's Manual

350-Watt Digital VHF LB Transmitter Chapter 5, Detailed Alignment Procedures
DT325B, Rev. 0 5-3
5.3.8 (A4-A1) 3 Way Combiner Board
(1198-1626; Appendix D)
There are no adjustments on this board.
The three +51.3 dBm Inputs are
combined to produce the 375 Watts
(+55.8 dBm) Output at J4 that connects
to the RF output jack J2 located on the
rear panel of the tray.
5.4 Calibration of the Output Power
of the VHF Amplifier Tray
Check that a Dummy Load of at least 400
Watts is connected to the Output of the
Tray that is to be calibrated. Switch S1
located on the AGC Control Board to the
Manual position before beginning the set
up. Adjust the front panel Meter for
100% Forward Output Power with R5,
Manual Gain Adjust, located on the AGC
Control Board.
Readjust the Manual Gain Pot for same
Spectrum Analyzer Reference Level.
Adjust R44 for 100% Forward Power
Reading. Calibrate the Front Panel
Output Power Meter to 100 % with R44,
Forward Power Meter Adjust, located on
the AGC Control Board. Lower the
Forward Power reading to 80% on the
front panel meter using R5, Manual Gain
Adjust, located on the AGC Control
Board. Adjust R65, AGC Fault Adjust,
located on the AGC Control Board until
DS3 the Green Module LED mounted on
the front panel just lights. Readjust the
Forward Power to 100 % using R5.
Switch the Tray Off and reverse the J6
and J7 cables located on the 3 Way
Combiner Board. Switch the Tray On and
adjust the front panel meter in the
Reflected Output Power Position to a 100
% reading using R53, Reflected Power
Meter Adjust, located on the AGC Control
Board. Adjust the Reflected Output
Power to a 20 % reading using R5
located on the AGC Control Board. Then
adjust R59, VSWR Cutback Adjust,
located on the AGC Control Board until
DS4 the Red VSWR Cutback LED
mounted on the front panel lights. This
sets up the VSWR Cutback Circuitry.
Readjust R5 for 100 % on the Meter for
250 Watts Output. Switch the Tray Off
and return the J6 and J7 Cables located
on the 3 Way Combiner Board back to
their original positions. Switch S1
located on the AGC Control Board to the
AGC position, which is the normal
operating position, after the set up is
completed.
There is a spare 1 Amp and 20 Amp
Fuse, located on the top, right rear of the
Tray, for replacement of the Fuses on the
Current Metering Board.
The VHF Low Band Amplifier Tray is
aligned and calibrated and ready for
normal operation.
5.5 Setting Up the Output Power of
the Transmitter
The following adjustments are
completed using the LCD screen located
on the front panel of the Axciter
Modulator Tray. On the Axciter Main
Screen, push the button next to the
Up/Downconverter tab on the right side
of the screen. This will open the
Upconverter/Downconverter Main
Screen. Set the AGC to Manual by
selecting 3 on the key board entry. The
screen will now indicate AGC Manual.
Set the transmitter to full power using
the Driver/Amplifier LCD display while
viewing the Power Control Screen in the
Set Up Menu and adjusting the level as
needed to attain 100% output power.
5.5.1 Setting up of AGC 1
To set up the AGC, first the AGC must
be activated. Locate the 8 position DIP
switch SW1 mounted on the Control
Board in the Axciter Upconverter Sled,
mounted in the Driver/Amplifier
Assembly. The Upconverter DIP Switch
Position 6 must be switched ON which
allows the user to modify the AGC 1 gain
through the Axciter Modulator.
See Figure 5-1 for an example of the
Axciter Upconverter/Downconverter