Pulse Generator

Turns the pulse generator on or off (with option R&S ZVA-K27). The pulse generator provides two independent control signals at the CASCADE output connector on the rear panel of the network analyzer. The signals can be used to control an R&S ZVAXxx Extension Unit equipped with a pulse modulator option.

Pulse generator signals consist of rectangular pulses which are repeated periodically. The signals serve as modulation signals for pulse modulators: During the high signal periods, the pulse modulator generates an RF signal, during the low signal periods, the RF signal is switched off. The R&S ZVA provides two different pulsed signals:

The Gen 1 signal (the actual "pulse generator signal") consists of a single pulse or a pulse train with selectable period. A pulse train is a series of pulses with individual timing and width. The pulse generator signal is not used internally.
The Gen 2 signal ("sync signal") is a single pulse which is repeated after the pulse period. The sync signal can be used as a trigger signal for pulsed measurements but also available as a modulation signal. In Chopped Pulse Profile mode, it is used chop the measured RF signal into short measurement intervals.

The pulse period of the pulse generator and sync signals are identical. An example for a pulse generator signal consisting of a pulse train (Gen1) and a sync signal (Gen 2) is shown below.

If not specified otherwise, the pulse generator settings are channel-specific.

A measurement example for pulse generators and pulsed measurements is reported in the Quick Start Guide for the extension unit R&S ZVAXxx, to be found on the R&S ZVA/B/T documentation CD-ROM.

To perform measurements on pulsed RF signals controlled by the pulse generator, the Pulse Gentrigger must be used. The trigger settings also control which of the trigger signals provides the trigger event.

Define Pulse Generator

Define Pulse Train

Defines a pulse train for the pulse modulator (Gen 1) signal on a segment-by-segment basis. This dialog is called from the Define Pulse Generator dialog.

Choose one of the following methods to efficiently create and handle pulse train segments:

To configure a pulse train with only a few segments, use Add Segment and edit each range in the table individually.
Use the Auto Arrange button to sort the segments in ascending order of the Start High Signal.
Save your pulse train definition to a file so you can re-use or modify it in later sessions (Save Pulse Train..., Recall Pulse Train...).

The Define Pulse Train dialog contains a table to edit the individual pulse segments; see below. The buttons below the table extend, shorten, or re-order the segment list.

The buttons above the table are used to import and export pulse train data. Pulse train files are ASCII files with the default extension *.train and a special file format.

Period denotes the duration of the entire pulse train. The period of the sync signal is adjusted to the pulse train period as long as the pulse train signal type is active.

The table contains an automatically assigned current number for each segment/pulse plus the following editable columns:

Active indicates whether the segment is active (checkbox selected) or inactive. Clearing the checkbox does not delete the segment but suppresses the pulse in the generator signal.
Start High Signal is the start time of the segment.
Stop High Signal is the stop time of the segment.

The minimum pulse width (the difference Stop High Signal –Start High Signal) is 12.5 ns. Segments/pulses may overlap, however, the largest Stop High Signal value must not exceed the pulse train Period.

Define Sync Generator

Defines the properties of the sync signal (Gen 2). This dialog is called from the Define Pulse Generator dialog.

The sync signal is either a single pulse signal with definite pulse width (Sync Width), following the pulse generator signal by a specified Sync Delay (to Pulse), or a constant signal. Constant signals (Constant High and Constant Low) need no further specification. It is possible to invert the polarity of the sync signal, i.e. to exchange the high signal and low signal periods.

While the pulse generator signal type is Constant High or Constant Low, the sync generator signal type is Constant High or Constant Low, too.

Adjust Settings for Chopped Pulse Profile

Defines the time resolution for the chopped pulse profile mode and activates the mode. This dialog is called from the Define Pulse Generator dialog.

Chopped pulsed profile mode is a means of achieving extremely small time resolutions for measurements on strictly periodic signals. Time resolution is the critical parameter for measurements on pulsed signals with very short pulse widths. In a normal time sweep at the default IF bandwidth of 10 kHz, the time resolution (i.e. the measurement time for each sweep point) is in the 100 μs range. In chopped pulse profile mode, the analyzer achieves time resolutions down to 12.5 ns.

A power calibration is generally not possible, however, the measurement provides accurate relative powers at consecutive sweep points. Hence the measurement result shows the profile of the measured RF signal.

Chopped pulse profile results are measured as follows:

The signal is chopped into k measurement intervals of equal width. The interval width is equal to the time resolution. For each interval, the analyzer acquires measurement results in n consecutive pulse periods. Due to the periodicity of the signal, the amplitude in each of the measurement intervals is equal. The results from the individual intervals are integrated; the effective measurement time per interval is thus n times the interval length. With a suitable selection of the factor n, this method provides accurate results at common IF bandwidths.

After integrating the n results for a given measurement interval, the analyzer steps to the next interval in order to repeat the procedure above. The total measurement for k measurement intervals covers k*n pulse periods. The measurement result is a time-domain trace consisting of k integrated measurement points.

The analyzer automatically selects a CW Time sweep mode and adjusts a number of data acquisition and pulse generator settings when the chopped pulse profile mode is activated:

The width of the sync signal pulse (Gen 1) is set equal to the time resolution. The sync signal controls the width and timing of the measurement intervals in chopped pulse profile mode. After each sequence of n measurements, the sync signal is delayed by one pulse width so that the next measurement interval is reached.
The period of the pulse generator signal (Single Pulse Period or Pulse Train Period, depending on the selected Pulse Type) is increased to the next integer multiple of the time resolution.
The number of sweep points k is calculated as the ratio of the extended pulse period to the time resolution.
The IF bandwidth is set to 1 over ten times the extended pulse period, and a high selectivity filter is used.

In remote control it is possible to skip measurement intervals (and thus accelerate the measurement, at the expense of the number of sweep points) by increasing the Delay Increment parameter.

File Format for Pulse Train Definitions

The analyzer uses a simple ASCII format to export pulse train definitions. By default, the pulse train file has the extension *.train and is stored in the directory shown in the Save Pulse Train and Recall Pulse Train dialogs. The file starts with a preamble containing the channel, the Pulse Train Period, and the Pulse Delay (to Sync) value. The following lines contain the entries of all editable columns of the list.