Use 5600 and 5142 seperately

[SunJab]

Hi,

I have 5661 (RF downconverter 5600 and digitizer 5142). I want to acquire the 15MHz IF signal of the downconverter through digitizer with DDC diabled(I don't want the IQ data centered around 0. I want to acquire the real 15MHz signal). For that i'll have to use the downconverter and digitizer seperately and have to configure 5600 in its downconverter only mode using niRFSA and 5142 using ni-scope. Is it possible to do that ? How can I pass the session handle from RFSA to ni-scope ?

thanx 

[jschwartz]

Hi Sandee,

To acquire a 15 MHz signal, you don't need to use the 5600 downconverter - you can just use the 5142 digitizer by itself.  The 5142 can sample at 100 MHz, which is more than enough to represent your 15 MHz signal.  You will not use the RFSA driver to use the 5142 as a stand-alone digitizer - you will use the NI-Scope driver. You can find many NI-Scope examples located at Start>>Programs>>National Instruments>>NI-SCOPE>>Examples.  Depending on your application, you should be able to find a good starting point from these examples.  The niScope EX Configured Acquisition VI is a great starting point that illustrates many of the features of the NI Scope driver.  

Message Edited by jschwartz on 06-07-2010 03:11 PM

[jschwartz]

Hi Sandee,

After taking a second look at your forum, I realized I did not read closely enough - you want to acquire the IF signal from the 5600.  Sorry about the confusion.  You can definitely do this.  I have attached a quick example that is basically combining an NI Scope example and the 5600 downconverter-only example.  I hope this helps.  

[SunJab]

Hi Jim,

Thanx for the reply. It really helped. I have a question. Why the 'span' property of niRFSA doesn't have any effect on the acquired signal? I acquired a signal by specifying a 20MHz span and it works fine. The signal spectrum shows all the available signals in the 20MHz span. But when I try giving it a different value (4MHz or 10MHz etc.), it still gives the same result and shows all of the signals in that 20MHz band. Why is it so?

thanx

[Andy_Hinde]

Hi Sandee,

The IF output of the PXI-5600 is always 20 MHz wide. Normally, this gets filtered down to the requested Span in the NI-RFSA settings by the OSP on the PXI-5142. The 5142 digitizes the full 20 MHz IF and then digitally downconverts, filters, and decimates (to the requested IQ Rate) the signal.

In your case, the OSP is disabled, so you will need to do any filtering of the IF signal yourself in software. 

The Span setting used in this example, which sets an NI-RFSA span while the NI-RFSA driver is operating the PXI-5600 in downconverter-only mode, is a little confusing in this case.The Span setting in this case is only used to set the tuning increment of the PXI-5600. The PXI-5600 tunes in either 1 MHz or 5 MHz steps, depending on the Span setting.

If the span is < 10 MHz, the PXI-5600 will tune in 5 MHz steps and have a narrower loop bandwidth, which slightly improves phase noise performance. This is the default setting of the attached example.

If the span is > 10 MHz, the PXI-5600 will tune in 1 MHz steps and have a wider loop bandwidth, which slightly degrades phase noise performance.

Regards,

Andy Hinde

RF Systems Engineer

National Instruments

Message Edited by Andy Hinde on 06-08-2010 09:07 AM