Axcera-430B FCC Type Acceptance Report Parts List/Tune-up Info
February 2004
7-2
Switch on the main AC and the VHF exciter circuit breakers on the AC distribution panel
behind the rear cabinet door.
7.2.1 High-Band VHF Exciter Tray with Baseband Video and Audio Inputs
The (A4) high-band VHF exciter tray (1070901)
has adjustments for video levels, audio
modulation levels, and other related parameters.
Connect an NTSC baseband video test signal input (1 Vpk-pk) to transmitter video input
jack J2 on (A12) the remote interface panel. Jacks J1 and J2 on the VHF exciter tray are
loop-through connected and the unused jack can be used as a video source for another
transmitter by removing jumper W4 on jack J3 on (A5) the sync tip clamp modulator board
(1265-1302). Connect a baseband audio input (+10 dBm) to the balanced audio input
terminal block TB1-1 (+), TB1-2 (-), and TB1-3 (ground). If stereo/composite audio is
provided, connect it to BNC jack J6, the composite audio input jack on the remote
interface panel. Jacks J3 and J13 on the rear of the exciter panel are loop-through
connected and the unused jack can be used as an audio source for another transmitter
by removing jumper W1 on jack J15 on the aural IF synthesizer.
Look at the front panel meter on the VHF exciter tray. In the Video position, the meter
indicates active video from 0 to 1 Vpk-pk. The normal video input level is 1 Vpk-pk on the
meter. If this reading is not at the proper level, the overall video level can be changed by
adjusting video level control R12 on the sync tip clamp/modulator board.
Switch the meter to the Audio position to show the audio deviation (modulation level) of
the signal from 0 to 100 kHz. The aural IF synthesizer board was factory set for a ±25
kHz deviation with a balanced audio input of +10 dBm. If the reading is at not the correct
level, adjust 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 a ±75
kHz deviation with a composite audio input of 1 Vpk-pk. If this reading is not correct,
adjust composite audio gain pot R17 on the aural IF synthesizer board, as needed, for the
±75 kHz deviation.
7.2.2 VHF Exciter Tray with the 4.5-MHz Composite Input Kit
With the 4.5-MHz composite input kit, (A4)
the
VHF exciter tray (1070901)
is able to
operate using either the separate video and audio baseband inputs or the single 4.5-MHz
composite input. The 4.5-MHz composite input kit includes a composite 4.5-MHz filter
board (1227-1244) and a 4.5-MHz bandpass filter board (1265-1307).
To align the VHF exciter using baseband video and audio, refer to the alignment
instructions described in Section 7.2.1. Select the baseband input operation by applying a
baseband select, using a jumper or closed contacts, connected between J7-6 and J7-7
on the rear of the tray.
To operate the transmitter using the 4.5-MHz composite input, remove the baseband
select command from J7-6 and J7-7 on the rear of the tray.
Connect a multiburst test signal from an envelope delay measurement set to the input of
the rear interface panel at J2. On (A24) the composite 4.5-MHz filter board (1227-1244),
connect an oscilloscope between J7, the center pin, and pin 1 or 3, which are ground.
Adjust C21, if necessary, for the best frequency response. Adjust R32 for a signal level of
1 Vpk-pk on the oscilloscope. The output, as measured at J6 and J7 on the board, should
be video-only with a minimum 4.5-MHz aural subcarrier.
On (A25) the 4.5-MHz bandpass filter board (1265-1307), adjust the filter with L2, C3,
L4, and C7 for a frequency response of no greater than ±.3 dB from 4.4 MHz to 4.6 MHz.
