User Manual

AMPLIFIER CONTROLLER BOARD REV.5
PUB12-030 Rev. 1 Feb 14, 2013 12-030-12 Amplifier Controller Board Rev.5
For ATSC Digital service, the above four jumpers would not be installed.
If the desired transmitter output power is the same as what the transmitter was originally set up for at the factory,
there should be no need to change the gain jumpers on the RF detectors.
If a change in power is required or the directional coupler has been changed or the transmitter is being moved
between Analog/Digital service, the RF detector should be first set to the lowest possible gain and the jumpers
moved to increase the gain.
For the forward power sample, the gain is controlled by jumpers E8 and E11. There are three possible gain
settings for these two jumpers
Low Gain: E11=LO
Mid Gain: E11=MID
High Gain: E11= Not Installed
For the reflected power sample, the gain works identically where E14 is the same as E11.
3.1.3 Verify OpAmp Offsets
1. With no RF signal applied, measure the voltage at U5 pin1 and adjust R58 to make this level under
0.1VDC
2. With no RF signal applied, measure the voltage at TP4 and adjust R80 to make this level under 0.1VDC
3.1.4 Verify Output Power Level
1. Attach the RF output power measuring device (Wattmeter or Average Power Meter) to the RF output.
2. Turn down the drive level of the modulator/upconverter before applying the RF input signal.
3. Turn up the drive level until the output power measures the desired reading. Do not use the meter of the
transmitter itself to determine output power, since at this point it may be uncalibrated.
4. When increasing the power, it is always instructive to measure the current on the 32VDC supply in case
there is a problem with how the output power meter is connected or working. If the supply current is
increasing but the output power is not, set the drive to a sufficiently lower level and double check your
setup.
5. When the RF output power is at the desired level, do the following checks:
a) For the forward power sample, the voltage at U5 pin1 should be within 4.5 to 9.0VDC as a
maximum
b) If not, then you have either too much power or too high a coupling in the directional coupler.
6. Reverify the output power: if this is correct, a pad can be inserted between the coupler and J12.
7. Adjust potentiometer R48 until the voltage at TP3 is 4.0VDC.
8. To calibrate the reflected power, install jumper E17 that prevents any VSWR trips
9. Remove the RF cable from J12 and attach a –10dB pad, then connect this reduced forward power
sample to J13.
10. If the original power sample into J12 required a pad, this must be retained in addition to the –10dB pad.
11. For the reflected power sample, the voltage at TP4 should be within 4.5 to 9.0VDC as a maximum
12. If not, reverify that the output power has not changed in the meantime.
13. Adjust potentiometer R80 until the voltage at TP5 is 4.0VDC.
Note: Make sure that you remove jumper E17 when done, else you will have no VSWR protection!
At this point, the operator should proceed to verify cutback and VSWR trip functions, as described in the next two
sections.