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Frequency Sweep Sync

Macro: SweepSync

The Sweep Sync control is available in the Frequency Sweep dialog whenever Sweep On is active.

When you toggle Sweep Sync on, it specifies that the display sync will be to the start of a sweep instead of the main waveform.

If the main wave Reset on Sweep control is active, this will result in a stable waveform if you are monitoring the signal output. In that case, the main wave phase is forced to the Phase setting at the start of each sweep. Otherwise, each sweep will start with the wave at whatever phase ended the prior sweep; the trace will appear to roll, even though the sync point is indeed at the start of the sweep. If you look carefully, especially on a sweep that covers a large frequency range, you can see that the trace appears more "open" on one end and more "compressed" on the other.

However, Sweep Sync is only effective if Trigger is active and Gen Sync is selected in the Trigger dialog. When the Gen Sync button has been activated there, it changes to show the current Sync source. In this case, it will show the channel and stream plus 'Sweep'.

If the Sweep Stairs option is active, Sweep Sync will sync the display to the start of a frequency step instead of the whole sweep. This is very useful for stepped frequency response measurements since it insures that the generated signal stays constant during the 1024 samples used to compute the spectrum, eliminating the spectral splatter from the step points. You must have Sweep Length set to more than 1024 samples per step for this to work.

Macro Notes:

L.1.SweepSync=1 sets Left Stream 1 Sync to the Sweep rate. L.1.SweepSync=0 sets Sync off, and L.1.SweepSync=x toggles between the two states.

Note that there is a single global Sync source, not separate sources for each channel or stream. The L.1. channel and stream prefixes select which stream will be chosen as the Sync source. When SweepSync goes from on to off, the global sync reverts to the Left Stream 0 Tone Frequency until you set it to something else.

Note: If a SweepSync command is given when the Sweep Dialog is open for any channel or stream, and the control is disabled in that dialog, then the macro will abort with an error message... regardless of which channel or stream is the target of the command. You can however, safely test SweepSync with an IF statement.

SyncMode is a read-only variable that returns the current sync mode. See the full description in the Tone Sync Macro Notes section.

See also Frequency Sweep, Waveform Stream Controls


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