3
6
6
10.
Check the VSWR OVLD trip point by setting the step attenuator for an additional 1dB of
attenuation. Press the momentary VSWR RESET switch to reset the transmitter and
remove the additional 1dB of attenuation from the step attenuator. The VSWR OVLD circuit
should again trip. If it does not, repeat this section beginning at step #6.
11.
Place the OPERATE/STANDBY switch to STANDBY. Return the Metering Coupler cables
to their original ports, J3 and J4. Reinstall the top cover, slide the drawer back into the
cabinet and secure it properly. Properly load the transmitter and place the Driver OPERATE/
ALIGN and OPERATE/STANDBY switches to OPERATE.
3.6
TU100FA Translator Power Calibration:
To ensure proper transmission, the output power level and % Power Meter calibration of the
translator should be checked once every year. With the meter switch in the FWD position, the
TUA100FA Amplifier % Power Meter has been factory calibrated for 100% with the translator
providing 100 watts peak visual and 10 watts average aural. The following calibration procedure
assumes that the composite signal received by the translator has the aural carrier 10dB down from
the visual with the visual carrier having 87.5% video modulation and 0% average picture level (APL).
In the following steps, the power levels stated are those expected at the output of the translator.
Therefore, when measuring these power levels as shown in Figure 3
6
7, be sure to take into account
the 30dB factor provided by the attenuator. Power levels at 50% APL (stair steps) are included in
brackets following the power levels at 0% APL (SYNC only).
This procedure also assumes the setup in Figure 3
6
7 is being used and that the output of the
receiver drawer has been correctly calibrated. If the received broadcast channel frequency is in the
VHF band (Ch.2-13), the mixer can be deleted from the test setup and a VHF agile modulator set
on the correct channel may be connected directly to the RF INput (J1) of the Receiver drawer
through an attenuator.
3.6a
Forward Power:
1.
With the TU20F Translator drawer in STANDBY and the TUA100FA Amplifier POWER ON
circuit breaker switch open (down), set up the test equipment as shown in Figure 3
6
7.
2.
Verify that the modulator is providing 87.5% video modulation with the aural 10dB below the
visual and that the input signal is at the correct frequency (Receiver’s input channel) and at
an amplitude between
!
40dBm to
!
47dBm. Place the TUA100FA 100 Watt Power Amplifier
into operation and make sure the Meter Switch is displaying FWD power. Turn the TU20F
Transmitter/Driver ON and place both the OPERATE/STANDBY and OPERATE/ALIGN
switches to OPERATE.
3.
To set the output power, adjust the Driver’s POWER ADJUST control 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].
