Checks and Adjustments
1720/1721
5–9
c. CHECK – that all of the vectors fall within ±1.25° and ±1.25 IRE
(NTSC and PAL-M), or ±1.25° and ±2.5% (PAL) of the target centers.
These specifications represent one-half the dimension from the center
cross of a vector target to the edge of the small inner box.
Perform steps d. and e. for the 1721 only:
d. Select the +V VECT MODE.
e. CHECK – that the Burst vectors can be overlaid with the PHASE
control.
6. Check Subcarrier Regenerator Performance
REQUIREMENT – Pull in range: F
SC
±50 Hz (±10 Hz for PAL or
PAL-M). Pull-in time less than 1 second. Phase shift at these frequency
offsets is within ±2°. Phase shift with ±6 dB burst amplitude within ±2°.
a. Connect the color bar signal to the CH-B INPUT. Display the signal in
VECT MODE.
b. Change the generator’s subcarrier frequency by ±50 Hz (±10 Hz for PAL
and PAL-M).
c. CHECK – that the 1720/1721 locks to the generator within 1 second at
these frequencies.
d. CHECK – that the vectorscope display does not change by more than
±2° at these frequencies.
e. Change the 1410-Series MOD AA output to black burst and vary the
Burst Amplitude + and –6 dB from the calibrated amplitude (1/2 to 2X
amplitude).
f. CHECK – that the 1720/1721 burst vector phase does not change by
more than ±2° within the + and –6 dB range.
7. Check Phase Accuracy
REQUIREMENT – Phase shift with signal input channel change less than
0.5°. Phase shift with +3 to –6 dB VAR GAIN change: less than 1°. Burst
jitter: less than 0.5°.
a. See Figure 5-4. Connect the color bar through a 75Ω feed-through
terminator and a dual input coupler to the CH-A INPUT and CH-B.
Connect the black burst signal to the EXT REF loop-through and
terminate in 75Ω. Select EXT REF. Alternately select INPUT A and B
in the VECT MODE.
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