The ZDLY record is used to change the displayed frequency scale for digital system analysis. Normally each DEL element in a digital system analysis corresponds to a normalized (one second) delay, for which the Nyquist interval is between 0.0 and pi radians per second or 0.0 and 0.5 Hz. The apparent Nyquist interval can be scaled by using the .ZDLY record. The format for the .ZDLY record is as follows:
.ZDLY F1
where
F1 : implied sampling interval. F1 defaults to 1.0, restricting the useful frequency range on an .AC record to 0.0 to .5 Hz (0.0 to pi rps) for an .AC analysis of a digital system.
Example:
.ZDLY 50.usec
Sets the apparent sampling rate to 20 KHz and the unit delay to 50 usec. The analysis frequencies on an AC record should be between 0.0 and 10.0 KHz to stay within the Nyquist interval.
Note that the use of the .ZDLY record is strictly for convenience. Network formulation for digital systems are based on a unit delay for each DEL element. The calculations performed by CCICAP use a scaled frequency appropriate for unit delays of one second. Identical results from a digital system analysis will occur by not using the .ZDLY record and restricting the requested analysis frequencies to between 0.0 and 0.5 Hz or 0.0 and pi rps.