FetchSpectrum Using Python and RFmx

[jmagers]

Hello,

I'm attempting to use RFmx through Python.NET.  The code works up until I try to grab the spectrum using FetchSpectrum():

# create variable name before passing it to .NET method
spectrum = RFmxSpecAnMXSpectrum

# This doesn't work!
specAn.Spectrum.Results.FetchSpectrum('', timeout, spectrum)

Here's the full code:

import clr
import sys

# location of assemblies
assy_path = r'C:\Program Files (x86)\National Instruments\MeasurementStudioVS2010\DotNET\Assemblies\Current'
sys.path.append(assy_path)

clr.AddReference("NationalInstruments.RFmx.SpecAnMX.Fx40")
clr.AddReference("NationalInstruments.RFmx.InstrMX.Fx40")

from NationalInstruments import *
from NationalInstruments.RFmx.InstrMX import *
from NationalInstruments.RFmx.SpecAnMX import *

# VSA Settings
resourceName = '5606_slave'
centerFrequency = 10.0e9        # Hz
referenceLevel = -10            # dBm
externalAttenuation = 0.00      # dB
timeout = 10                    # seconds
span = 1.0e+6                   # Hz
rbw = 100e3
averagingCount = 10

instrSession = RFmxInstrMX(resourceName, '')

# configure VSA
rbwAuto = RFmxSpecAnMXSpectrumRbwAutoBandwidth.True
rbwFilterType = RFmxSpecAnMXSpectrumRbwFilterType.Gaussian
averagingEnabled = RFmxSpecAnMXSpectrumAveragingEnabled.False
averagingType = RFmxSpecAnMXSpectrumAveragingType.Rms
#specAn = instrSession.GetSpecAnSignalConfiguration();
specAn = RFmxSpecAnMXExtension.GetSpecAnSignalConfiguration(instrSession)
specAn.ConfigureRF('',centerFrequency,referenceLevel,externalAttenuation)
specAn.Spectrum.Configuration.ConfigureSpan('', span)
specAn.Spectrum.Configuration.ConfigureRbwFilter('', rbwAuto,rbw,rbwFilterType)
specAn.Spectrum.Configuration.ConfigureAveraging('', averagingEnabled,averagingCount,averagingType)
specAn.SelectMeasurements('',RFmxSpecAnMXMeasurementTypes.Spectrum,bool())
specAn.Commit('')

# execute acquisition
specAn.Initiate('','')

# find peak power in the spectrum
_,pkAmp,pkFreq,freqRes = specAn.Spectrum.Results.FetchMeasurement('',timeout,float(),float(),float())
print 'Peak Power: {:0.2f} dBm at {:0.6f} GHz'.format(pkAmp,pkFreq*1e-9)

"""
A .NET method may require the user to pass the variable name it wishes to
modify as an argument. Python does not support "pass by reference" but the
variable name must exist in python before it can be handed to the .NET method.
The .NET method will simply point to the new instance.

http://nbviewer.ipython.org/github/jonnojohnson/Agilent/blob/master/Python_Automation/Python_Automation.ipynb
"""

# create variable name before passing it to .NET method
spectrum = RFmxSpecAnMXSpectrum

# This doesn't work!
specAn.Spectrum.Results.FetchSpectrum('', timeout, spectrum)

instrSession.Close()   

Here  is the error:

Traceback (most recent call last):

  File "<ipython-input-172-79fb463146f0>", line 3, in <module>
    specAn.Spectrum.Results.FetchSpectrum("", timeout, spectrum)

ArgumentException: Object of type 'System.RuntimeType' cannot be converted to type 'NationalInstruments.Spectrum`1[System.Single]&'.
   at System.RuntimeType.TryChangeType(Object value, Binder binder, CultureInfo culture, Boolean needsSpecialCast)
   at System.Reflection.MethodBase.CheckArguments(Object[] parameters, Binder binder, BindingFlags invokeAttr, CultureInfo culture, Signature sig)
   at System.Reflection.RuntimeMethodInfo.InvokeArgumentsCheck(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture)
   at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture)
   at Python.Runtime.MethodBinder.Invoke(IntPtr inst, IntPtr args, IntPtr kw, MethodBase info, MethodInfo[] methodinfo)

Any ideas?

[JMota]

See below for a reponse from a colleague that saw this post and is well-versed in the RFmx .NET API:

"I am not able to reply to it due to network issues. Can you please reply to the query and indicate that the spectrum type he/she is using is wrong.

# create variable name before passing it to .NET method
spectrum = RFmxSpecAnMXSpectrum

Should actually be

# create variable name before passing it to .NET method
spectrum = NationalInstruments.Spectrum<float> #Present in NationalInstruments.Common assembly"

Hope this takes care of the issue.

[jmagers]

Hi JMota,

Thanks for the reply.  I gave that a try, and I received the same error.

# import the "NationalInstruments.Common assembly"
import NationalInstruments

# create variable name before passing it to .NET method
spectrum = NationalInstruments.Spectrum[float]

print spectrum
<class 'NationalInstruments.0, Culture=neutral, PublicKeyToken=b77a5c561934e089]]'

For reference, if I eliminate the [float]:

# create variable name before passing it to .NET method
spectrum = NationalInstruments.Spectrum

print spectrum
<class 'NationalInstruments.Spectrum`1'>

[JMota]

Got some more info from another colleague. Just passing it along:

"Thats not how you call ref/out parameters from iron python. There are two ways

A. Implicit: you just don't pass ref and out params. And the python will return all ref and out parameters as a tuple.

B. Explicit: use clr.Reference[T] and then pass that."

Hope that sheds some light.

[va_me_ni]

Here is a minimal example that shows how to call FetchSpectrum:

import clr
import sys


# location of assemblies
assy_path = r'C:\Program Files (x86)\National Instruments\MeasurementStudioVS2010\DotNET\Assemblies\Current'
sys.path.append(assy_path)

clr.AddReference("NationalInstruments.RFmx.SpecAnMX.Fx40")
clr.AddReference("NationalInstruments.RFmx.InstrMX.Fx40")
clr.AddReference("NationalInstruments.Common")

from NationalInstruments import *
from NationalInstruments.RFmx.InstrMX import *
from NationalInstruments.RFmx.SpecAnMX import *
from System import *

# VSA Settings
resourceName = '5606_slave'

instrSession = RFmxInstrMX(resourceName, '')

specAn = RFmxSpecAnMXExtension.GetSpecAnSignalConfiguration(instrSession)
specAn.SelectMeasurements('',RFmxSpecAnMXMeasurementTypes.Spectrum,bool())
specAn.Commit('')

# execute acquisition
specAn.Initiate('','')

# create variable name before passing it to .NET method

spectrumDataRef=clr.Reference[Spectrum[Single]]();
result=specAn.Spectrum.Results.FetchSpectrum('',10.0,spectrumDataRef);
spectrumData=spectrumDataRef.Value;
print 'Spectrum size: {0}'.format(spectrumData.SampleCount)
instrSession.Close()

[jmagers]

I gave that a try, but the clr module doesn't appear to have a "Reference()" method. Perhaps this is an IronPython implimentation, rather than Python.NET?

In[11]: dir(clr)
Out[11]: 
['AddReference',
 'FindAssembly',
 'ListAssemblies',
 'NationalInstruments',
 'System',
 '_AtExit',
 '__class__',
 '__doc__',
 '__file__',
 '__name__',
 '_extras',
 'clrmethod',
 'clrproperty',
 'getPreload',
 'setPreload']

[va_me_ni]

Yes this is the IronPython implementation. I wrongly assimed that you were using IronPython.

You implmented this fix.

# import the "NationalInstruments.Common assembly"
import NationalInstruments

# create variable name before passing it to .NET method
spectrum = NationalInstruments.Spectrum[float]

 Instead of

spectrum = NationalInstruments.Spectrum[float]

can you please try

spectrum = NationalInstruments.Spectrum[float](0)

[jmagers · Accepted solution]

Ah! That was just about it. Here's what worked:

spectrum = NationalInstruments.Spectrum[System.Single](0)
_,spectrum = specAn.Spectrum.Results.FetchSpectrum('',timeout,spectrum)

Here is the result and the final code for future reference:

import clr
import sys
import os
import matplotlib.pyplot as plt
import numpy as np

# Windows environmental variable for Program Files

program_files = os.environ['ProgramFiles(x86)']
assy_path = os.path.join(program_files,
                         'National Instruments',
                         'MeasurementStudioVS2010',
                         'DotNET',
                         'Assemblies',
                         'Current')
                         
sys.path.append(assy_path)

clr.AddReference("NationalInstruments.Common")
clr.AddReference("NationalInstruments.RFmx.SpecAnMX.Fx40")
clr.AddReference("NationalInstruments.RFmx.InstrMX.Fx40")

from NationalInstruments.RFmx.InstrMX import *
from NationalInstruments.RFmx.SpecAnMX import *
import NationalInstruments
import System

# VSA Settings
resourceName = '5606_slave'
centerFrequency = 25.0e9      # Hz
referenceLevel = -10          # dBm
externalAttenuation = 0.00    # dB
timeout = 10                  # seconds 
span = 1.0e+6                 # Hz
rbw = 100e3                   # Hz
averagingCount = 10

instrSession = RFmxInstrMX(resourceName, '')

# Get model number
_,model=instrSession.GetInstrumentModel('',str())

# configure VSA
rbwAuto = RFmxSpecAnMXSpectrumRbwAutoBandwidth.True
rbwFilterType = RFmxSpecAnMXSpectrumRbwFilterType.Gaussian
averagingEnabled = RFmxSpecAnMXSpectrumAveragingEnabled.False
averagingType = RFmxSpecAnMXSpectrumAveragingType.Rms
specAn = RFmxSpecAnMXExtension.GetSpecAnSignalConfiguration(instrSession)
specAn.ConfigureRF('',centerFrequency,referenceLevel,externalAttenuation)
specAn.Spectrum.Configuration.ConfigureSpan('', span)
specAn.Spectrum.Configuration.ConfigureRbwFilter('', rbwAuto,rbw,rbwFilterType)
specAn.Spectrum.Configuration.ConfigureAveraging('', averagingEnabled,averagingCount,averagingType)
specAn.SelectMeasurements('',RFmxSpecAnMXMeasurementTypes.Spectrum,bool())
specAn.Commit('')

# execute acquisition
specAn.Initiate('','')

# get x data
spectrum = NationalInstruments.Spectrum[System.Single](0)
_,spectrum = specAn.Spectrum.Results.FetchSpectrum('',timeout,spectrum)

# get y data
analogwaveform = NationalInstruments.AnalogWaveform[System.Single](0)
_,analogwaveform = specAn.Spectrum.Results.FetchPowerTrace('',timeout,analogwaveform)

# close session
instrSession.Close()

# compute frequency and power
startFrequency = spectrum.StartFrequency
frequencyIncrement = spectrum.FrequencyIncrement
sampleCount = spectrum.SampleCount
stopFrequency = startFrequency + frequencyIncrement*(sampleCount+1)
freqArray = np.linspace(startFrequency,stopFrequency,sampleCount)
power = list(analogwaveform.GetRawData())

# plot results
xscale = 1e-3
plt.plot((freqArray-centerFrequency)*xscale,power,linewidth=2.0)
#plt.ylim(referenceLevel-100.,referenceLevel)
plt.yticks(np.linspace(referenceLevel-100.,referenceLevel,11))
plt.xticks(np.linspace(-span,span,11)/2*xscale)
plt.xlim(-span/2*xscale,span/2*xscale)
plt.grid(True)
plt.xlabel('Relative to Center Frequency (kHz)')
plt.ylabel('Power (dBm)')
plt.title("{} Spectrum at {:0.6f} GHz".format(model,centerFrequency*1e-9),fontsize='medium')
plt.show()

[JMota]

Very nice. Glad to see you got it to work.

[jmagers]

thank you for the help!