Software Defined Radio
Overview
This example demonstrates the ability of the NI-USRP to demodulate multiple FM signals across a bandwidth of several MHz (essentially, an FM channelizer). Different stations can be switched to without stopping to re-tune to a new center frequency since they are acquired simultaneously.
Description
This multi-channel FM reciever/channelizer works by taking a wider range of bandwidth (the default is set to 5MHz here, to maximize compatibility with various setups) during the acquisition. This data set is then passed using a queue structure to a processing loop that will re-center the acquired spectrum based on the center frequencies given for each FM station, downsample each station to the bandwidth of an FM signal (about 200kHz), and then demodulate to retrieve the audio signal at each station.
The user can select which of the acquired stations to play over the computer's audio, though the other audio signals acquired will still appear in the "Audio Channels" indicator to demonstrate that they are being simultaneously acquired. Though possible with this example, it wouldn't be very productive to try to play audio from all of the stations at once. This example is intended to serve more as a proof of concept for applications where processing multiple demodulated signals in parallel is desired.
To run, simply open the project attached, and run the MultiChannelDemod VI. Set the desired Center Frequency, and note that the Channels of Interest will need to be within +/- half of the I/Q rate from the Center Frequency, to meet bandwidth requirements.
Below is a screenshot of the program in action, with a few radio stations playing that are local to Austin, Texas:
