User's Manual

3300-Watt VHF Low Band Transmitter Chapter 5, Detailed Alignment Procedures
335B, Rev. 0 5-7
panel lights. This sets up the VSWR
cutback circuitry.
Readjust R5 for 100% on the meter to
achieve a 750 watts peak of sync output
+ 75 watts aural power. However, if the
system requires less output power per
amplifier tray, adjust each tray by the
same amount to give the desired total
output power.
Switch off the tray and return the J6 and
J7 cables on the 3-way combiner
assembly, back to their original positions.
If the tray was originally operating below
100% output power, the AGC fault adjust
was set for 20% below the operational %
Output Power of the tray. See the Test
Data Sheet for the transmitter for the
actual readings for the tray. Place S1 on
the AGC control board in the AGC
position. This is the normal operating
position after the setup is completed.
The VHF amplifier tray is aligned,
calibrated, and ready for normal
operation. Repeat as needed for the
other VHF amplifier trays.
5.7 Phase and Gain Adjustment of
multiple VHF Amplifier Trays
The following procedure was completed
at the factory and should only be
followed if one of the VHF amplifier trays
is replaced.
Adjust the gain controls located on the
VHF Amplifier Trays full CCW. Switch On
the front panel AC Circuit Breaker on the
bottom VHF amplifier tray. Place the
Transmitter in Operate and adjust the
Gain control on the Amplifier Tray for
50% output power and adjust the Phase
control to mid range. Monitor the output
power of the Transmitter by connecting a
Spectrum Analyzer to a sample of the
output. Adjust the Spectrum Analyzer
for Zero Span operation. The power
could be monitored by watching the
meters on the panel but the power
change is easier to see on the analyzer.
Turn On the AC to the middle amplifier
tray and adjust its' output power to 50%.
While monitoring the output power of the
Transmitter, adjust the Phase Control
until the power reaches a peak. If the
Phase adjust reaches its end of travel,
add a 4 inch cable to the RF Input (J1) of
the amplifier. Re-adjust the Phase to
peak the System output power. If the
Phase Control again reaches its end of
travel before a peak in power is reached,
add a 3 inch cable to J1 of the amplifier
and readjust phase for peak output
power. The adding of cables should be
done during the adjustment anytime the
range of the phase adjust needs
extended.
Turn On the AC to the top amplifier tray
and adjust its' output power to 50%.
While monitoring the output power of the
Transmitter, adjust the Phase Control
until the power reaches a peak. If the
Phase adjust reaches its end of travel,
add a 4 inch cable to the RF Input (J1) of
the amplifier. Readjust the Phase to
peak the System output power. If the
Phase Control again reaches its end of
travel before a peak in power is reached,
add a 3 inch cable to J1 of the amplifier
and readjust phase for peak output
power. The adding of cables should be
done during the adjustment anytime the
range of the phase adjust needs
extended.
Increase the output power on the bottom
and middle amplifier trays to 90%.
Adjust the Phase Control on the middle
amplifier tray to peak the System output
power.
Increase the output power on the top
amplifier to 90% and adjust the Phase
control for maximum System output
power.
Monitor the Reflected Power on all of the
VHF Amplifier Trays. The Reflected
Power should read <5%. If an amplifier
is showing high reflected power, adjust
the Phase control as needed to minimize