3
6
5
2.
Verify that the modulator is operating and providing 87.5% video modulation. Place the
100 Watt Amplifier POWER switch to ON and make sure the Amplifier’s Meter Switch is in
the FWD position. Place the TTU20F Transmitter STANDBY switch to OPERATE.
3.
To set the output power, adjust the TTU20F POWER ADJUST for an external power meter
reading of 69.5W [44W]. Note that 100W peak visual at 0% [50%] APL and 87.5%
modulation plus 10W average aural equals 69.5W [44W] average power.
4.
To check or adjust the visual to aural carrier ratio, replace the power meter in Figure 3
6
6 with
a spectrum analyzer. Adjust the aural carrier level on the modulator for the desired ratio.
Remove the spectrum analyzer and return the power meter to the Transmitter’s output and
reset the output power for an external power meter reading of 69.5W [44W].
5.
With the external power meter showing the correct power, place the meter switch to FWD
and check the TUA100FA front panel % Power Meter for a 100% indication. If this reading
is not obtained, adjust potentiometer R9 of the Metering Detector (A3) for a 100% indication.
The Metering Detector is mounted on the right-hand side wall near the front of the amplifier
drawer and is accessible through the holes in the side wall. The % Power Meter on the
TTU20F Transmitter/Driver will indicate less than 100% which is an appropriate reading.
3.5b
Reflected Power (
OPTIONAL
):
6.
On the right side wall of the TUA100FA Power Amplifier drawer, adjust potentiometer R30
of the Metering Detector fully clockwise to disable the VSWR overload detection circuit.
Place the amplifier drawer meter switch to REFL.
7.
Place the Transmitter/Driver OPERATE/STANDBY switch to STANDBY and the OPERATE/
ALIGN switch to ALIGN. Remove and reverse the forward power (J3) and reflected power
(J4) coupling port cables on the Metering Coupler (DC1). J1 and J3 of the Metering Detector
(A3) should now be connected to J4 and J3 of the Metering Coupler (DC1), respectively.
This simulates an open circuit at the amplifier's RF OUTput (J2) delivering maximum
returned power to the REFL port of the Metering Detector. Insert a step attenuator between
the modulator's IF OUTPUT and the transmitter's IF INPUT and set the step attenuator for
10dB attenuation.
8.
Place the Transmitter/Driver OPERATE/STANDBY switch to OPERATE. Remove the
attenuation from the step attenuator for an external power meter reading of 69.5W [44W].
Check the amplifier drawer's front panel REFL meter for a 100% [70%] reading. If
necessary, adjust potentiometer R27 of the amplifier Metering Detector for the proper
reading. R7 is accessible through the right-hand side wall of the drawer.
9.
Decrease the transmitter's power to 50% by increasing the step attenuator 3dB for an
external power meter reading of 34.75W [22W]. This power level is used for setting the trip
point of the VSWR overload detection circuit. Adjust R30 of the amplifier’s Metering Detector
slowly counterclockwise until the front panel VSWR OVLD indicator illuminates red and the
Transmitter/Driver is placed in standby.
