Axcera-430B FCC Type Acceptance Report Parts List/Tune-up Info
February 2004
7-11
response. Adjust R32, video gain, for a signal level of 1 Vpk-pk on the oscilloscope.
The output at J6 and J7 on the board should be video-only, without the 4.5-MHz aural
subcarrier.
7.2.12.4 (Optional) 4.5-MHz Bandpass Filter Board
This board is part of the 4.5-MHz input kit and will only function properly with a 4.5-MHz
composite input signal and the 4.5-MHz composite input selected. To align this board:
1.
Adjust the filter with L2, C3, L4, and C7 for a frequency response of no greater than
±0.3 dB from 4.4 MHz to 4.6 MHz.
2.
Adjust C19 for an overall peak-to-peak variation of less than ±0.3 dB from 4.4 MHz
to 4.6 MHz.
3.
Recheck the frequency response; it may have changed with the adjustme nt of the
envelope delay. If necessary, re-tune the board.
7.2.12.5 IF Carrier Oven Oscillator Board
To align this board:
1.
While monitoring J3 with a spectrum analyzer, observe the 45.75-MHz visual IF
(t5 dBm).
2.
Connect a frequency counter to J3 and adjust C17 for 45.750000 MHz.
3.
Connect a frequency counter to J1 and check for 50 kHz, which is the aural phase
lock loop (PLL) reference.
7.2.12.6 Sync Tip Clamp/Modulator Board
To align this board:
1.
Determine if jumper W4 on jack J3 is present. Jumper W4 terminates the video input
into 75
Ω
. Remove jumper W4 if a video loop-through is required on the rear chassis
at jacks J1 and J2.
2.
Set the controls R20, the white clip, R24, the sync clip, and R45, the sync stretch
cut-in, to their full CCW position. Set R48, the sync magnitude, fully CW and place
the jumper W7 on jack J4 to the Clamp -Off, Disable, position.
3.
Connect a 5-step staircase video test signal to the input of the transmitter.
4.
Monitor TP2 with an oscilloscope. Adjust R12, the video gain pot, for 1 Vpk-pk.
5.
Change the video input test signal to a multiburst test pattern. While monitoring
TP2, adjust C8 and R32 for a flat-frequency response. Change the input video test
signal back to the 5-step staircase.
6.
Monitor TP2 with an oscilloscope. Adjust pot R41, manual offset, for a blanking level
of -0.8 VDC. The waveform shown in Figure 7-1 should be observed at this point.
Move jumper W2 on J4 to the Clamp Enable position. Adjust pot R152, depth of
modulation, for a blanking level of -0.8 VDC.
Note: This waveform represents the theoretical level for proper modulation depth.
