5142 New

[madd]

Hello

Greatefull for ur relpies NI. I have new question. what if i want to acquire a signal greater than 50Mhz using 5142. lets say i want to acquire a 70Mhz signal. Alisaing will be the result and my signals aliased componet will now lie at 30Mhz within the nyquist spectrum.And now i can fileter this signbal out using band pass filter and store it to my disk . Am i write ?. Also with the bandwidth of 40Mhz it will lie from 10Mhz to 50Mhz Yes or No?

Regards

Madd

[Speedy_Badger]

Hello Madd,

This will depend on what you set your maximum frequency to. If you set the max frequency to -1 via the Config Chan Characteristics VI you will use the full 100 MS/s and the anti-aliasing filter will be disabled. In this instance you will see both the 70 MHz tone and the aliased 30 MHz tone +- your bandwidth in each case. If you enable the anti-aliasing filter via the same VI mentioned, 35 MHz for instance, you will not be able to take advantage of this phenomena without the effects of attenuation.

I did a quick experiment to illustrate this. I generated two tones, one 68 MHz tone at -5 dBm and one 72 MHz tone at 0 dBm and acquired at an NCO frequency of both 70 MHz and 30 MHz. My IQ rate was 40 MS/s.

Full BW

Left @ 30 MHz, Right @ 70 MHz

Anti-Alias Filter

Left @ 30 MHz, Right @ 70 MHz

Notice the >60 dB attenuation in the second case - this correlates to the frequency response of the anti-alias filter documented in the 5142 section of the NI Digitizers Help file.

Regards,

Message Edited by Speedy Badger on 03-11-2009 11:10 AM

Message Edited by Speedy Badger on 03-11-2009 11:12 AM

[madd]

Hello I have another question. I am using baseband example of niscope(5142) to acquire two sine waves from channel 0 and channel 1 . when I look at the waveform and spectrum of the signals. Signal acquired from channel 0 is attenuated 45db w.r.t channel 1. niscope express VI gives the same result.(when coupling is DC and resistance is 50ohm, when auto setup is enabled then working fine). Wile using the above mentioned example. If I set the coupling to Ac and resistance to 1Mohm. Type of acquisition is not supported error comes.Why is this attenuation there?

[Jordan F]

Hi

I ran a few examples to try and recreate the functionality you are seeing but have been unsuccessful.  Could you give some more information (frequency of input signal, screenshots, connections, etc.) to help me figure out what phenomena you are experiencing.  I did find that the setting of AC coupling and 1Mohm impedance is an acceptable setting for this device.  The only setting that is not allowed is AC coupling with 50ohm impedance (I received the same error you did while using these settings).  Also, I believe that when you auto set the device, it sets the coupling to AC and the input impedance to 1Mohm.  Were you only  

I tried running the niScope EX Advanced Measurement Library.vi and niScope EX Digital Filtering.vi to see if I could get any differences between the two input signals but did not see any attenuation. 

[Chris_W.]

Hello Madd,

Because your question on this post is the same as on other threads, we would like to consolidate your posts to one thread so that everyone who is interested can follow the progress of your issue. All further activity on this issue will continue on thread linked HERE. Thanks.

Chris W