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Demodulate and Listen to FM Radio with NI USRP

FM Radio  – Arctangent Method

Summary:

Use the NI USRP as a spectrum analyzer to find local FM radio stations and then modify the block diagram to decode the FM radio station and listen to the music.

Requirements:

·         NI USRP-2920 (most radio stations fall between 88 MHz and 108 MHz

·         Ideally an FM antenna, but any small wire may work

·         Radio station reception (not a good demo for the basement, use the video)

Demo Procedure:

Find an FM Radio Station (Spectrum Analyzer)

1.       Open the VI: FM_Radio_Spectrum.vit

2.       Verify the correct IP Address of your USRP is set under device names (typically 192.168.10.2)

3.       Run the VI (Note: if it errors try and decreasing the number of samples to 10,000)

4.       Disable Auto Scale X by right clicking on the graph and zoom into a radio station to see its frequency (remember that 0 on the graph represents the carrier frequency on the left)

5.       Point out that the bandwidth of the radio station is +/- 100kHz (a total of 200kHz bandwidth)

Troubleshooting:

1.       Boost the gain: Try boosting the gain try: 10, 25, and 30

2.       Still no stations: Stop the demo here and show the video.

Listen to Live FM Radio

6.       Change the carrier frequency to that of the radio station you found

i.e.  If the center frequency is 94.7M and the station appears at -1M, set the new radio staion frequency to 93.7M

7.       Decrease the IQ rate to 200kHz

8.       You may want to turn Auto Scale X back on

9.       Change windows to the block diagram (CTRL + E)

10.   Grab the VI’s from the Disabled Diagram structure and drop them on the block diagram

[Note: If the VI's are unable to link in the Disable Diagram structure, simply open each of the VIs in the subVIs folder and they should re-link automatically]

11.   Wire in the brown wire in the middle to the first VI and memorize the following wiring:

image004.jpgimage005.jpg

Figure 1: VIs to be wired shown two ways, with icon view and terminal view

12.   Talk through the process:

a.       Determine the phase of the complex IQ signal

b.      Unwrap the phase to remove discontinuities at +/- 180 degrees

c.       Take the 1st derivative of the phase, this is frequency and the output is equivalent to the information in the FM signal

d.      Finally resample is used to reduce the data rate to be compatible with the soundcard

13.   Wire the orange tunnel on the left of the while loop to the

14.   Delete the brown waveform wire to the right of Sound Output Wirte.vi and wire the top output terminal of Resample Waveform to the shift register.

15.   Finally, delete the VI going into the PS/PSD VI and wire in between the Derivative and Resample Waveform VIs.

image006.gif

Figure 2: Complete VI wiring

16.   Switch back to the front panel (Ctrl-E)

17.   Run the VI

18.   You’ve now demodulated broadcast FM radio using the mathematical approach

Troubleshooting:

1.       Distortion: can be caused by applying too little gain or too much! Try increasing the gain or decreasing the gain methodically.  Use the first part of this demo, the spectrum analyzer to troubleshoot.

2.       Breaks in the audio: The sound VI’s are less than ideal.  Try decreasing the number of samples to a very small number like 10,000.  Some sound cards just don’t work well.

Files:

·         FM_Radio_Spectrum.vit

o   Demo VI (saved as a VI Template)

To learn more about the NI USRP visit ni.com/usrp

Comments
Member gauraangKhurana
Member
on

Hey, I am unable to use the above file.

When I tried to open the (.vit) file. I get this error.   I am new to USRP and Labview.

PLEASE HELP ME

Error2.PNG

Error.PNG

Member sahasra
Member
on

Screenshot (4).png

Hiee I am new to labview and i find the error asshown in screen shot please help me resolving the error

muffin.vi
NI Employee
on

sahasra,

Do you have the NI-USRP driver installed? You will need this to interface with the hardware.

Member sahasra
Member
on

How Should I interface

NI-USRP driver with hardware?Please help me out doing so ...thank you in advance 🙂

Member sahasra
Member
on

I am not able to find some sub vi's in the attachment and I am observing certain question marks in the block diagram

Poly VI 'niUSRP Fetch Rx Data (poly).vi':SubVI is missing

Poly VI 'niUSRP Open Rx Session.vi':SubVI is missing

Poly VI 'niUSRP Initiate.vi':SubVI is missing

Poly VI 'niUSRP Configure Signal.vi':SubVI is missing

Poly VI 'niUSRP Abort.vi':SubVI is missing

Poly VI 'niUSRP Close Session.vi':SubVI is missing

Member sahasra
Member
on

i observed these errors and modified the as block diagram as follows.kindly plzz help us solving this issue..thanks in advance block diagram.jpgmmmmmmmmmmmmmmmmmmmmmmm.png..

muffin.vi
NI Employee
on

sahasra,

I reccomend opening a service request with NI Support. It looks like something in your software setup is incorrect. Make sure you have the correct drivers installed and and that you have unzipped the download.

Member MoahmmadFayiz
Member
on

Sahasra

all subVIs you missed in your run is because of either you didnt install the USRP driver or there is aproblem in installing software, please check if you installed  http://www.ni.com/download/ni-usrp-15.0/5679/en/ .

I hope this helps you.

Member tomnz
Member
on

I think there is a problem with your sound out vis. They appear to be a little old and perhaps obsolete in some versions of LabView. I have all the drivers. I changed one of the vis. to a newer one for write out and it appeared to solve the problem.

Member tomnz
Member
on

Excellent example. I can see the spectrum and the audio appears under it. Despite a lot of fiddling with sound settings though nothing comes out of my sound card. I tried digital out too. I am working on that.

More important though I saw another example similar using LabView communication and it worked fine including sound, but with such a setup how do you change the channel in real time? It seems the frequency is set and initialised and then it goes into the while loop. How to change the frequency as in a real radio with a knob.

Member tomnz
Member
on

I got the audio working. Still wonder how to have a tuning knob though and scan through the airwaves.

Member g0910353
Member
on

請問 下面那4個問號 我USRP 也有安裝 還是我還有少安裝甚麼 以至於讀不到 下列4個套件VI (新手上路 不好意思

image.png

Member g0910353
Member
on

I would like to ask the following four question marks. I have installed the USRP or I still have less installed so that I can't read the following four kits VI.

Sorry, I was the last one to ask the question.

Member g0910353
Member
on

Thank you for finding these four components VI.

Member XTOPHER
Member
on

Hello everybody,

I think that the enclosed video file is unavailable yet. Someone could send me the video file?

Thanks a lot,

Best regards

Contributors