H Heuer Instruments UMDT51A, User Manual

Page: 27 / 104

Testing VF-PCM Multiplexers
LT51 User Manual 15
Signal to Quantization Noise
1. Make the connections between the Test circuit and the LT51 as in Fig. 3.1.
2. Turn the LT51 ON. [after Reset: Ztx = 600

, Zrtx = HiZ 600

, TX Source =
OFF, TX Freq =10 kHz, Mode = TX-RX (4W)]
3. Press the button, then the [f2] soft-key to set Input
to ‘Term’. The
LT51 RTX (input) impedance is now 600

terminated.
4. Press the key, followed by the [f1] soft-key to set the frequency Span .
Use the knob to set the span to 4.5 kHz.
5. Press the [f3] soft-key to set BW
to ‘PSOPH’ to make psophometric
weighted measurements.
6. Press the key followed by the [f3] soft-key to set the TX Source to
‘SINE’.
Press the [f4] soft-key to set the TX Freq to 1014 Hz using the Knob or
Keypad, and press the button to clear the Dialog box, or appropriate
[fx] soft-key if using keypad.
7. Press the key, followed by the [f1] soft-key to set Level to make a
‘S/ND’ (Signal to Noise and Distortion) measurement, which is equivalent to
the S/Nq measurement.
8. Repeat for all levels at the steps in the Specification template.
9. The display will show the Psophometric weighted Signal to Quantisation
Noise ratio measured at the LT51 RTXab input terminals. Press
(Spectral) or (Numerical) to toggle between displays of the signal.