HP 37717C Calibration Manual page 320

Figure 3-59
Figure 3-60
Performance Tests
STS-3 Transmitter Output Waveshape (Option 120)
STS-3 All Ones Pattern
STS-3 All Ones Mask
CMI All Zeros Waveshape
7. Select PATTERN [ALL ZEROS] on the OTHER DEBUG FUNCTION display.
3-211