Continental Electronics 816R - PA Tuning and Loading; Maximum Power Output Adjustment

operating parameters should be performed
only after the transmitter has stabilized.
22. RAISE or LOWER the POWER ADJUST
control until the POWER OUTPUT meter
displays the station's authorized power level. If
specified by the customer, the meter was
calibrated at the factory to indicate 100% at this
power.
23. Compare meter readings with those listed in the
factory test data.
24. Set POWER CONTROL switch to
AUTOMATIC. Adjust the power
monitor/control card A2A6R8, located in the
card cage, for 100% output power if necessary.
C. ANTENNA SYSTEM VSWR CHECK
The REFLECTED POWER OUTPUT meter should not
indicate more than five percent which is a VSWR of
1.57. The transminer is set at the factory to trip OFF
at ten percent Reflected Power. Typically, VSWR is
less than 1.1:1 which is less than 0.25 percent
Reflected Power.
D. PA TUNING AND LOADING (For best
efficiency).
Fig. 1, PA Plate Tuning
There is not likely to be a plate current dip within the
normal range of tuning control. There are, however,
three indicators to be observed for proper PA TUNE.
Power output and screen current will be maximum. PA
plate current will change as the tuning is changed. Plate
current will increase when the tuning control is held in
the raise position. When the shorting plane is positioned
correctly, the PA screen current and power output will
go through a peak. Refer to Figure 1 for an indication of
what to expect as the tuning control is run through its
total mechanical range, from one limit to the other.
Notice that power output is the same at point A and
point B, but that plate current is greater at point B. The
proper tuning point is at point A which results in
maximum output and also the least amount of plate
current (not plate current dip). The loading control is
adjusted for maximum RF output. PA screen current
decreases when loading is raised and increases when
loading is lowered. Normally, screen current is between
150 - 550 mA. The screen current is dependent upon
loading, power output requirements, plate and screen
voltage, and individual tube characteristics. When the
PA tube is replaced, screen voltage may have to be
changed in order to obtain the desired power output.
E. MAXIMUM POWER OUTPUT ADJUSTMENT.
NOTE
This procedure is intended to maintain
authorized station maximum power output with
line voltage variations.
1. Set the POWER ADJUST control to RAISE
until maximum power output is displayed on the
POWER OUTPUT METER.
2. If the maximum power output is not more than
5 % above the authorized station maximum
output, skip to Step h. If the maximum power
output is more than 5 % above the authorized
station maximum output, proceed to Step c.
3. Press the PLATE OFF and FILAMENT OFF
switches on control panel Al.
4. Turn off primary power to the transmitter.
5. If TPO is greater than 15 kW, the Plate
Transformer taps are set to match the line
voltage. The Screen Transformer has primary
and secondary taps which are used to set the
transmitter to the desired TPO plus about five to
ten percent headroom. The Screen Transformer
secondary taps are 70%, 85%, and 100%
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