Harris Platinum Series Technical Manual Download Page 72

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For transmitter models which use one or more 10 kW or 15 kW
cabinets, the individual PA cabinets are calibrated at their rated
peak of sync power levels, and the peak detectors are calibrated
to 2.5 volts at this power level.

HT1, HT2, and HT5 transmitters use different calibration voltage
values for the peak detectors. The visual peak detectors are set to 1.8
volts, and the aural peak detectors to 0.8 volts, at the rated power. This
is necessary because of the tradeoff required when adjusting couplers
for desired coupling and maximum directivity at these lower power
levels.Alowcouplingfactor(typically37.5dB)mustbeusedtoachieve
adequate forward to reflected directivity. If the directivity is too low,
forward power flow will affect reflected power readings, resulting in
errantly high VSWR readings for low values of reflected power.

If directional coupler detector bias adjustments are necessary,
perform them using the procedudre provided in paragraph 5.11.2
before calibrating forward power. If a reflected peak detector
adjustment is necessary, it is performed after forward power
calibration, if necessary.

5.12.1

Directional Coupler Alignment

The directional couplers have been factory set and will not
require any adjustment. Some special systems may use adjust-
able couplers. The coupling ratio and directivity must be selected
to provide an in-range sample with good directivity for monitor-
ing forward or reflected power.

The peak detectors on the Slave and Main controllers require
+12 dBm (17 mW) at the input jack to deliver approximately 3
volts DC at the cathode of the detector diode. This allows some
headroom in setting the 2.5 volt calibrate points.

If a coupler must be set in the field, use the following procedure:

a. Measure the loss in the sample cable. Calculate the ratio

of 17 mW to the stage power being measured, in dB. The
result will be negative.

b. 10 log(0.017/power in watts)=

-_____dB.

c. Compensate the coupling ratio for the cable loss by adding

the cable loss as a positive value. This gives the forward
coupling needed.

d. Remove the directional coupler line section from the sys-

tem, and set up the equipment per Figure 5-3.

e. Connect the exciter and spectrum analyzer input cables

together through attenuator pads equal in value to the
coupling ratio. Set a reference on the analyzer.

f. Remove the pads. Re-connect the exciter to the line section

and the coupler to the analyzer.

g. Adjust depth of coupling in the forward mode to the

reference level.

h. Reverse the connection of the exciter and the load, and

adjust the coupler rotation for minimum reflected indica-
tion, noting the directivity. A minimum of 30 dB directivity
is needed for measurements used to control interlocks, but
more directivity gives better accuracy.

i. Repeat the depth and rotation adjustments until the desired

coupling ratio and directivity values are reached.

j. Re-install the line section in the system and calibrate power

of the stage.

5.12.2

Peak Detector Bias

The bias of each detector diode has been set at the factory, and
should not be disturbed unless a component is replaced or a
specific problem is noted. With no RF input applied, read the
power indicated by the display panel for the detector being
calibrated. Use a DMM to read the voltage of the detector diode
cathode. Slowly increase the bias of the cathode (10-30mV
approximately) until the last digit of the display reading changes
from 0 to 1; then back off slightly, returning the reading to 0.

When bias is adjusted, the calibration of the detector in question
must be checked as well.

5.12.3

Reflected Power Peak Detector Calibration

The forward power calibration of the peak detector is outlined later
in this chapter. To calibrate the reflected power, first calibrate the
forward power peak detector meter reading. Disable the exciter
foldback on the Main Controller board by placing DISABLE
JUMPERS J18 & J19 in the 2-3 positions. Next, rotate the reflected
coupler sample element located in the line section to read forward
power and calibrate (R87 Vis Ref & R91 Aur Ref) the reflected
power reading to read the same power as the forward power meter
reading. Rotate the reflected coupler sample elements back to the
reflected power position. Return jumpers J18 & J19 to the foldback
enable position 1-2. This completes the reflected power calibration.

5.12.3.1

Rev. H Main Controller

With version E11 or later software, the forward and reflected
power meter readings can indicate a small power reading (<10
watts) when the transmitter is off. This is because the peak
detector voltage follower output does not track the detector
voltage near 0 volts. Later models (Rev. “H”) of the Main
Controller PC board use a +12 volt supply for the voltage
followers, which allows each follower output to track the peak
detector input near the 0 volt level.

5.13

Visual RF Power Calibration

5.13.1

Single-Cabinet Transmitters

Turn the transmitter ON and apply blanking and sync test signal
to the exciter. Be sure no “SET-UP” is used. Use external meter-
ing at the output port and adjust the average output power to the
corresponding value below:

B/PAL

Model

M/NTSC

B/SECAM

HT1

.595 kW

.568 kW

HT2

1.19 kW

1.14 kW

HT5

2.98 kW