User's Manual

3300-Watt VHF Low Band Transmitter Chapter 5, Detailed Alignment Procedures
335B, Rev. 0 5-5
(1142-1601) in Manual. The idling
currents for the amplifier boards are
adjusted with no RF drive applied.
Remember to put S1 back to the Auto
AGC position after any adjustments.
Auto AGC is the normal position during
operation of the transmitter.
Connect a dummy load with a rating of at
least 750 watts to J2, the RF output jack
of the tray being aligned, before
beginning the alignment procedure.
Switch the VHF amplifier tray on and the
transmitter to operate.
5.6.1 (A13) AGC Control Board
(1142-1601; Appendix D)
Using a calibrated wattmeter, check that
the tray is operating at the rated power.
Remove the sample forward power
connection J4 from the (A13) AGC control
board (1142-1601). The output power
level should drop to 20% because of the
VSWR cutback and DS4, the VSWR
Cutback LED, should be illuminated. The
front panel Module Status LED should not
be lit.
Reconnect J4 and adjust R59 so that it
begins to cut back on the output power
level when the reflected level increases
above 20%.
In the Power Supply Voltage position, the
front panel meter is calibrated to +30
VDC using R86 on the AGC control board.
5.6.2 (A2-A1) Phase Shifter Board
(1198-1602; Appendix D)
There are no adjustments to (A2-A1) the
phase shifter board (1198-1602). The
front panel has adjustments for phase
that are made during the amplifier array
setup procedure. Typically +7 dBm input
and +7 dBm output.
5.6.3 (A2-A2) VHF Filter/Amplifier
Board (1198-1606; Appendix D)
The (A2-A2) VHF filter/amplifier board
(1198-1606) has approximately 14 dB of
gain. Tune the channel filter capacitors
C29 and C20 (loading), C26 and C23
(center frequency), and C24 (coupling) at
J6 on the board for the best response.
Set voltage adjust pot R19 for +24 VDC
at the anode of CR5.
The idling current, no RF drive applied, of
the device Q1 is set for 250 mA. To set
the current, remove the RF drive,
measure the voltage across R16 (a 1Ω
resistor on the filter/amplifier board) and
adjust R13 for .25 volts (using Ohms’
Law: [E=I x R] : [E=250 mA x 1 Ω] :
E=250 mV). Typically the board has a
+7 dBm input and a +19.5 dBm output
level.
5.6.4 (A3-A1) VHF Low-Band
Amplifier Board (1198-1605;
Appendix D)
The (A3-A1) VHF low-band amplifier
board (1198-1605) has 22 dB of gain and
is biased for 3 amps of idling current, no
RF drive applied. Adjust voltage adjust
pot R10 for +24 VDC at pin 0 of the
regulator IC U1. To set the bias, remove
the RF drive from the board, measure the
voltage across R6 and R7 (two 1Ω
resistors in parallel on the high-band
driver board), and adjust R4 for 1.5 volts
(using Ohms’ Law: [E=I x R] [E=3 amps
x .5 Ω] : E=1.5 volts).
Connect a spectrum analyzer to output
jack J2 on the board and adjust C15 for
peak output. Typically +19.5 dBm input
and +41.5 dBm output.
5.6.5 (A3-A2) Overdrive Protection
Board (1198-1601; Appendix D)
The typical input level to the (A3-A2)
overdrive protection board (1198-1601)
is +41.5 dBm during normal operation
with a typical output of +41.3 dBm.
To set up the overdrive circuit, check that
the output power level of the transmitter
is at 100% and adjust R11 on the board
for a reading of .4 VDC at TP1. Increase
the output power level of the transmitter