on Feb 7, 2017How do I create CW and FMCW?
How do I create CW and FMCW?
The N5193A UXG supports 2 types of Pulse Descriptor Words (PDWs).
The first is a pulse and is specified with start time and width.
The second is a CW PDW and is specified with start time.
The CW PDW stays on until the next PDW or CW PDW.
The RF output can be on or Off for CW PDWs so it is possible to turn off the CW PDW after a given period of time.
The N7660B software uses the Signal Object under Waveforms to make use of the CW PDWs.
Two important properties are Period and Segment Time.
Because the hardware doesn’t have an independent way of applying an antenna scan or Doppler to a CW signal, MESG breaks a signal into segments.
The segments are continuous in that there is no off time between them.
However, each segment can have a different amplitude, frequency, and phase offset.
This makes it possible to apply antenna scans and Doppler shifts.
The CW PDWs only support linear chirp modulation.
The other modulations PSK and FSK are created by MESG using segments within the signal period.
When creating Signals with Linear Chirp modulation, MESG breaks the chirp into segments when segment time is less than the signal period.This makes it possible to have wide chirps at lower RF frequencies.
The UXG spec for chirp bandwidth of 10% of RF frequency is circumvented as a bunch of smaller chirps are stitched together.
Creating FMCW waveforms requires the WC1 option.
Click on the ‘Waveform’ level in the Simulation Explorer.
In the Property View, click the ‘Plus’ sign and add a Signal. Double check ‘use instrument streaming mode.’
The ‘Period’ of the Signal is how often it repeats. The ‘Segment Time’ is used to control the resolution of the antenna scan amplitudes independent of the frequency or phase modulation. The latter is set in the ‘Modulation Type.’