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HELP: Simple AM RX/TX?

Its now been four days and still no response from the service request. Does NI not have an example for AM? It seems to me that quite a few people have NI-USRP's, has no one tried to receive a transmitted AM signal?

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Message 11 of 19
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Hi Kyosake, have you heard back yet on the service request?  Unfortunately we haven't been able to find a standard USRP AM example, but are experimenting with FM examples.  You could potentially experiment yourself with the FM examples found at ni.com/examples to ensure that the HW is functioning properly.

Andy G
Applications Engineering
National Instruments
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Message 12 of 19
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I was told it was being worked on three days ago. . .

 

I have experimented with the the FM examples but I cant seem to get anything but static.

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Message 13 of 19
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Hmm have you been able to use this USRP for other applications successfully in the past?  Can you use the standard shipping examples to simply transmit and receive data?

Andy G
Applications Engineering
National Instruments
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Message 14 of 19
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Yes, i have been able to use the examples. The examples are a bit overwhelming complicated though. If i can get a basic am transmission and reception working, it would greatly increase my understanding of how this equipment works. I dont want to rely on modifying other people's code.
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Message 15 of 19
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Hi Kyosake,

 

We've been looking over some other customers' issues in the past when dealing with AM with a USRP, and it sounds like the mismatch in signals may actually be expected behavior on USRP due to a combination of LO Leakage that needs to be compensated for, and a DC offset that needs to be introduced on the receiving end. NI USRPs are based on Zero-IF Architecture. LO feed-through is expected behavior from these type of architectures. The corrections are done digitally to suppress LO feed-through.  

 

 

 Please test the attached VIs, which should be able to provide the necessary compensation.  The receive VI includes the following modifications--

  1. Use the undocumented function to turn off an unwanted filer
  2. Add a constant of 1 to the received signal to create a necessary DC offset
  3. Use a USRP property node to move the LO out of the way--specifically set the LO to a value near to, but not exactly the carrier frequency (eg 1 MHz away).  Try experimenting with different LO values

 

In terms of understanding generic USRP functionality, you can refer to the following link--http://www.ni.com/usrp/getting-started/

Andy G
Applications Engineering
National Instruments
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Message 16 of 19
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Thanks a lot! I'll give it a go and report back within a few days.
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Message 17 of 19
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Can you help me check whether my vi is correct or not? I didn't get the desired results:the Modulation Depth(%) =0.3, the amplitude of Rx singal =0.3, when I send the Tx singal(the Modulation Depth(%) =0.3).
I didn't know whether the carrier amplitude through MT Demodulate AM VI is correct or not? Or get the carrier amplitude from other method.

Please tell me how can I modify it!

Why aren't equal in the amplitude of Tx and Rx signal????

Thank you!

Tx.pngRx.png

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Message 18 of 19
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The modified code works great, I did however have to replace the code with a MATLAB script because I couldn't run a math node. Now, I'm going to see if I can playback the received signal. I also need to look more into LO leakage and the required DC offset to fix it, as they are a new concept to me.

 

School just started, so I wont have a whole lot of time to experiment with the VI's, but if I have any further questions or figure out the playback I will post here.

 

Torry, hopefully one of the NI guys can answer your question since I am still working on understanding how AM works on the USRP's.

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Message 19 of 19
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