After becoming familiar with the NI5640R, our team developed a software defined AM radio using a homemade antenna which passes through a LP filter with a cutoff frequency of 5MHz as the analog input to the card.
The host was then reconfigured to have a decimation value of 256 since we were only concerned with a single radio frequency at baseband. The acquired data was then AM demodulated, sent through a digital filter, and decimated further to account for the specifications of the computer speakers. The decimated array was then used to build a sound waveform. Using the appropriate sound VIs, the waveform was played.
We created two hosts which play this waveform--one of which plays it using a finite sample and another which plays it continuously. The finite sample radio simply builds a finite array when the host is started. Once stopped, the built waveform from the collected data is played through the speakers.
The continuous sample radio continuously builds the waveform and plays it while building the next waveform; however, some problems occur here. The processing time used to manipulate the acquired data allows for some lag when the sound is being played. We found this out by playing a normal AM radio at the same time as the LabVIEW AM radio and noticing the delay. Also, not only does the software radio delay, once the number of samples per channel is reached, the radio repeats a portion of the output sound which increases the delay from the real radio even further. Both the delay and the time at which the radio repeats is directly proportional to the number of samples/channel.
Now that we have a better understanding of configuring the host, we would like to do the previous on the fly using the FPGA. This would allow for no delays and faster processing on the host.
We have attached our work up to now. The sample rate of the sound format should be set to 48828.125 Samples/second and 16 bits/sample. If have any questions or suggestions, please post them here.
Troy Perales
Mobile Integrated Solutions Laboratory
Texas A&M University
