Harris Platinum HT EL 2000LS, Technical Manual

Page: 49 / 90

5.6.2
Visual Peak-sync to Average Power Conver-
sion Formulas
Measurement of RF power has historically been done using
directional couplers with diode detecting elements that can be
calibrated against calorimetric standards. This allows the meas-
urement of average RF power. TV transmission systems are
rated in peak power, referred to as peak-sync or sync peak
power. The ratio between peak and average power is easily
calculated if the moduletion is simple, consisting only of sync.
The formula is shown in Table 5-1.
Table 5-1 includes the results of typical calculations.
Use values from Table 5-1 or independent calculations in the
following power calibrations.
5.7
Transmitter Metering and Control
Calibration
Meter board calibration (located in the exciter)
Each function on the Digital Display and Bar Graph is individu-
ally calibrated as follows:
5.7.1
Power Supply Meter Calibration
5.7.1.1 PS VOLTS Calibration:
a. On the Interface Logic Board connect a Digital Voltmeter
(DVM) to 1A3TP10 (50 V Supply Voltage Sample) and
Ground.
b. Turn on the Transmitter. The DVM should read 1.75
+/-0.25 volts at 1A7TP10 for a supply voltage of 50 V
DC.
c. Select PS VOLTS on the Exciter Meter.
d. On the Exciter Meter set R1 (PA V CAL) for 50% on the
Bar Graph, 10 segments illuminated.
e. Adjust R95 (PA V CAL) for and indication of 50.0 on the
Digital Display.
5.7.1.2 PS CURRENT Calibration
This is factory adjusted. Use a precision current shunt and meter
if recalibaration is needed.
a. Select PS CURRENT on the Exciter Meter.
b. On the Exciter Meter set R2 (PA I CAL) to match the
measured current on the Bar Graph. The Bar Graph reads
120 A full scale (20 segments).
c. Adjust R94 (PA I CAL) for numeric indication the same
as the measured current.
5.7.2
Exciter RF Output Meter Calibration
5.7.2.1
Exciter Visual Power Calibration
a. Connect an RMS low power wattmeter to 1A8J2 (VIS RF
OUT).
b. Using black picture power operating conditions, adjust
vision exciter power output to the average value deter-
mined in paragraph 5.6.2.
c. Select EXC VIS on the Exciter Meter.
d. On the Exciter set R3 (EXC VIS CAL) for full scale on
the Bar Graph.
e. Adjust R97 (EXC VIS CAL) for a numeric indication of
1.000 watts.
5.7.2.2
Exciter Aural Power Calibration
a. Connect an RMS low power wattmeter to 1A8J3 (AUR
RF OUT).
b. Adjust the aural power to 1.00 watts on the power meter.
c. Select EXC AUR on the Exciter Meter.
d. On the Exciter set R4 (EXC AUR CAL) for full scale on
the Bar Graph.
e. Adjust R96 (EXC AUR CAL) for a numeric indication of
1.000 watts.
5.7.3
Transmitter RF Output Meter Calibration
Initial Setup for Calibration:
Preset the following Jumpers:
Jumper Position
JP1 Visual Foldback 2-3
JP2 Aural Foldback 2-3
JP3 Aural AGC 2-3
JP12 Visual AGC 2-3
JP16 High VSWR Shutdown 2-3
The transmitter must be operational with visual and aural con-
nected to a calibrated load and wattmeter. The visual modulated
with a black picture, 40 units of sync.
Table 5-1. Peak to Average Ratio
Section V - Maintenance
888-2457-001 5-3
WARNING: Disconnect primary power prior to servicing.