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Unformatted text preview: 1 EE102 Spring 2009-10 Lee Systems and Signals Project Project Due: Friday June 4 For this project, we will look at signals from the AM band, write an AM receiver as an m-file, and listen to the demodulated signals. The data was captured using a Universal Software Radio Peripheral (USRP). This is an open- source project to develop radio transmitters and receivers that are USB peripherals, and that can be configured to handle almost any type of signal. It uses a 66 MHz A/D, and a programmable gate array to capture the signal, which can then be processed in software on your computer. The data comes from Michael Gray, and his web site http://www.kd7lmo.net . He has examples of quite a few different signals he’s captured, including GPS, FM, HF, and others. The data we’ll be looking at is the AM band that we covered in Lecture. The capture is of about 30 seconds of a large part of the band. The AM spectrum in the US goes from 520 kHz to 1610 kHz, with channels separated by 10 kHz. The data is in the matlab file am_data.mat on the following website. http://dl.dropbox.com/u/5613612/am_data.mat . It has 15 seconds of data sampled at 256 kHz. The signal has already been demodulated by 600 kHz once using a quadrature receiver. If we just lowpass filter and detect the envelope, we’d hear the station at 600 kHz. Unfortunately, the strong signals are elsewhere! We need to first find the signals, then demodulate to the right frequency, and then use an envelope detector to extract the audio waveform....
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- Spring '09
- Digital Signal Processing, kHz, Fourier series coefficients, AM band