disable OSP

[Alann]

Hey,

Can we disable the Onboard Signal Processing in NI 5142? If yes then how?

[muks]

Looking for this?

[Alann]

any other way to do this? like if i want just the real digitized data. No conversion in IQ.

[muks]

I am not sure whether u can do that.

[HSD]

If you want to frequency shift the data and low pass filter the data for real data only, you can look at the example niScope EX OSP Downconversion that is included with the driver.

If you just want base band decimation (no frequency shifting, but still filtering out all alias), you can look at the example niScope EX OSP Baseband Decimation.  This examlpe returns complex data, but the real component is channel 0 and the imaginary component is channel 1.

[Alann]

Well .. I am new to the NI world. Just started using the digitizers. Can you please highlight what are options in configuration of NI 5142? What are the main features of OSP I can play with?

What is meant by CONFIGURABLE IF bandwidth?

If I disable or enable OSP, what characteristics of the signals can be compared?

If i have a signal of 10MHz sampled at 14MHz (less than Nyquist, span 20MHz), why NISCOPE doesnt show the aliased spectrum? (even when anti-alias filter is disabled)

How do we enable/disable the noise filter?

What is the best way to understand the working and controls of digitizer NI 5142?

hah! a million questions .. help me navigate through NI world

[HSD]

If navigate through the start menu -> program files -> national instruments -> NI-Scope -> documentation ... you can find the NI High-Speed Digitizers help file.  Inside the help file if you click on Devices, you will see all the devices that niscope supports.  Expand the NI 5142 menu and you will see all the general help you are asking for.  In specific the Onboard Signal Processing tab has all the details about the osp you are curious about.

Now for your questions:

Configurable bandwidth is special on this devices.  If you have the OSP enabled, the bandwidth is 80% of the sample rate for complex data and 40% of the data for real data.  For example a sample rate of 10 MS/s would have 8 Mhz of bandwidth for complex acquisitions and 4 Mhz of bandwidth for real mode acquisitions.  Make sure you query the actual sample rate attribute to see what the actual sample rate of the device is.  The driver might coerce the sample rate you set if the hardware can not achieve it.

The OSP can be configured in many ways, so it depends on how you configure it.  The main blocks are a FIR filter, a digital gain/offset block, NCO (mixing in frequency domain), low pass filter/decimation block.  The last two blocks combine to create a DDC (digital down conversion).  Digital Down Conversion allows you to capture a subset of the frequency spectrum and shift the frequency content down to baseband.  This is frequency used in RF applications to reduce the data through put of the system for band limited signals.

You should be seeing the aliased specturm if you have the OSP disabled.

The noise filter is disabled/enabled using the maximum input frequency attribute.  The attribute can also be set on the configure channel characteristics function.

Hope this helps,  I would high recommend reviewing the niscope examples and documentation.  It won't answer all your questions, but I'm sure it will help.

Thanks