Language Reference

ADCTRG

External trigger frequency can a￿ect measurement accuracy

For external ADC triggering, connect the signal to the rear-panel EXT TRIG IN connector. To delay external ADC triggering, refer to \ADCTRGDLY".

When using external ADC triggering in non-zero spans, the frequency of the external trigger signal can a￿ect measurement accuracy. The trigger signal's frequency must be greater than

frequency > 1:5 (trace length ) : sweep time

In some cases, a factor as high as 2.0 may be required instead of 1.5. If the ADC trigger rate is too low for the current combination of trace length and sweep time, the warning message 16005 Sweep too fast is displayed. This warning is reported once for every sweep where the external trigger doesn't occur often enough.

Avoid oversweeping the When using external ADC triggering, displayed video bandwidths are

video bandwidth not accurate and care must be taken not to over sweep the actual video bandwidth. Use the following equation to estimate the actual video bandwidth:

video bandw idth ￿ (factor) (displayed bw) (external trigger frequency) 27; 000

where:

factor is a function of the external trigger frequency. factor is always less than 1.0 and may be as low as 0.5.

To obtain the proper sweep time, estimate the actual video bandwidth (as described above), and then set the optical spectrum analyzer's bandwidth to that setting. Then, use a computer to query the coupled sweep time. Refer to the ST command in this manual. The value returned to the computer is the proper sweep time setting.

Query Response

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