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NI RFSG AWG (phase modulate a signal using code from a GPIB Arbitrary Waveform Generator)

I am new to PXI Hardware.  I am trying to generate a modulated signal using NI PXI/e vector signal generators using some intercepted GPIB commands from rack mounted (GPIB) instruments, an RF Signal Generator and Arb function generator.  I know the RF Signal Generators settings including: frequency, amplitude, modulation set to phase, phase deviation, and  modulation source set to external.  For the Arb function generator I know the voltage peak to peak, frequency, and the series of 1's and 0's stored to memory that create the arb waveform.  Connecting the Arb to a scope it looks like it's outputting a series of pulses.

 

How do I replicate this using NI-RFSG?  I have a 5672 (PXI-5610 & PXIe-5442) or 5673E (PXIe-5450, PXIe-5611, & PXIe-5652) vector signal generator that I can use.

 

Thanks.

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Hi JMU_ISAT,

 

I am a little confused about your application and what you are trying to do/what you have already done.  

  • Are you trying to send out a modulated signal from your 5672/5673?  
  • What code did you previously run with your Arb and RF sig gen?

It sounds like you are using Modulation Toolkit based on the settings that you mentioned.  You can use Modulation Toolkit with either of the VSG devices that you have.  There are examples for the toolkit that can be found by going to Start » All Programs » National Instruments » Modulation » Examples.  That will be a good place to find VIs that can send out a modulated signal from your VSG device.  Please let me know a little bit more about your system and your overall applications so I can better help you get started with NI-RFSG.

Sarah Yost
Senior Product Marketing Manager
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Old Setup:

 

Agilent E4438C VSG

-set freq

-set amplitude

-set modulation=phase

-set modulation source=external

 

Agilent E33250A Function/AWG

-set freq

-config volt (peak to peak)

-store specified series of 1's and 0's to memory (message to be used as modulation source/pattern) to be used to define the arb waveform points

**********************

 

How do I replicate the above using NI-RFSG / PXI VSG / Modulation toolkit?  How do I configure the modulation source / arbitrary waveform for the PXI VSG?  I am not familiar with I/Q data, etc.  I simply want to phase modulate an RF signal as defined by the same series of 1's and 0's/pulses as done previously.

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Thanks for the details, I have a much better understanding of what you are trying to do now.

 

First, in order to use your VSG as a VSG instead of 2 or 3 individual modules, you need to tell the driver software which cards belong to which device.  This is done using Measurement & Automation Explorer.  You will only need to do this once.  Here is a link to the RFSG Help file with details of how to do this:

 

Associating Devices in MAX

http://zone.ni.com/reference/en-XX/help/371025K-01/rfsg/associating_devices/

 

The NI VSG devices function by using an IQ modulator architecture, but if you just want to send in 1s and 0s that make up your waveform, this is easy to do.  All you need to do is select "Arb Waveform" for the generation mode of the niRFSG Configure Generation Mode.vi.  I picked an example that should be close to what you are trying to do to use as a starting point.  You didn't mention if you wanted to do analog phase modulation (PM) or digital (phase shift keying or PSK), but I chose the MT RFSG Generate PM.vi (found in the examples folder I mentioned in my last post).  First, a bit stream is generated using the Basic Function Generator.vi.  Next it is sent to the MT Modulate PM.vi where the signal is modulated based on information that you provide.  After the modulated signal is created, that signal is fed into niRFSG Write Arb Waveform.vi.  The data fed into that VI will be written out to your Arb.  After it is turned into an analog signal on the arb, it will be upconverted and transmitted out of the upconverter to the center frequency that you specify.  This example could be easily modified by removing the Basic Function Generator.vi and replacing it with your bit stream. 

 

Two important differences about the NI VSG products compared to the Agilent ones are:

  • The Arb and the upconverter function together with one driver, and all communication to these 2 devices is done with the RFSG driver. 
  • The modulation is done in software.  After the bit stream is generated, software is used to perform the modulation.  Then that modulated signal is built using the Arb, upconverted, and transmitted

Let me know if this exploitation is confusing, I would be happy to help answer any questions about the information above.  

Sarah Yost
Senior Product Marketing Manager
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