Data Sheet

835A 4kW, 5kW or 6kW UHF Transmitter Detailed Alignment Procedure
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(A1) UHF Exciter Tray - Continued
Connect an NTSC Composite Video Test Signal Input (1 Vpk-pk) to the Transmitter Video Input Jack J2, located on (A9) the
Remote Interface Assembly. Connect a Baseband Audio Input (+10 dBm) to the Balanced Audio Input Terminal Block TB1
or if Stereo/Composite Audio Input (1 Vpk-pk) is provided, connect it to the BNC Jack (J6) the Composite Audio Input Jack.
Observe the Front Panel Meter located on the UHF Exciter Tray. In the Video Position the Meter indicates Active Video from
0 to 1 Vpk-pk. With an Input Video of 1 Vpk-pk the display should indicate 1 Vpk-pk at White. If these readings are not the
proper levels, the overall Video Level can be changed by adjusting the Video Level Control (R12), located on (A5) the Sync
Tip Clamp/Modulator Board (1265-1302).
Switch the Meter to the Audio Position which indicates the Audio Deviation (Modulation Level) of the signal, from 0 to 100
kHz. The Aural IF Synthesizer Board was factory set for ±25 kHz deviation with a Balanced Audio Input of +10 dBm. If the
reading is not the correct level, adjust the Balanced Audio Gain Pot R13, on the Aural IF Synthesizer Board, as needed to
attain the ±25 kHz deviation. The Aural IF Synthesizer Board was factory set for ±75 kHz deviation with a Composite Audio
Input of 400 Hz @ 1 Vpk-pk. If the reading is not correct, adjust the Composite Audio Gain Pot R17, on the Aural IF
Synthesizer Board, as needed for the ±75 kHz deviation.
The Upconverter Section of the UHF Exciter Tray includes adjustments for automatic level control (ALC), linearity (amplitude
predistortion) and incidental phase (phase change vs. level) predistortion for correction of the nonlinearities of the RF
Amplifier Trays. The Upconverter Section also includes adjustments of the local oscillator chain tuning and also the local
oscillator center frequency tuning. Both of these were completed at the factory and should not require adjustment at this time.
Move the Operate/Standby Switch located on the UHF Exciter Tray to Standby.
The set-up of the RF Output includes the adjustment of the Linearity and Incidental Phase Predistortion which compensate for
any nonlinear response of the Amplifier Trays and also the gain and phasing adjustments of the UHF Amplifier Trays in each
of the Amplifier Assemblies.
Verify that all Red LEDs located on the ALC Board are extinguished. The following list details the meaning of each LED
when illuminated.
DS1 ......... Input Fault. Indicates that the Input level to the board is low or missing.
DS2 ......... Indicates that the ALC circuit is unable to maintain the signal level requested by the ALC reference.
Normally this is due to excessive attenuation in the linearity or ICPM corrector signal path or that Jumper W3 on J6
is in the Manual ALC Gain position.
DS3 ......... Indicates a loss of Video at the Input of the board.
DS4 ......... Indicates a Visual Mute Command is present. Not used in this System.
Check that the Jumper W3 on J6 on (A8) the ALC Board (1265-1305) in the Auto Position and adjust the Power Gain Pot,
located on the Front Panel of the UHF Exciter Tray, to obtain +0.8 VDC on the Front Panel Meter in the ALC Position. Move
the Jumper W3 on J6 to the Manual Position and adjust R87 on the ALC Board for +0.8 VDC on the Front Panel Meter in the
ALC Position. Move the Jumper back to Auto which is the normal operating position.
The detected IF signal level at J19-2 of the ALC Board is connected to the Transmitter Control Board that distributes the level
to the Phase/Gain Trays. The (A4 & A5) Phase/Gain Trays connects the ALC voltages to the Metering Panel which splits the
references which are connected to the Amplifier Assemblies where they are used as the reference for the automatic gain control
(AGC) for each Amplifier Tray.