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ATmega8 Based Radio Spectrum Monitor with FFT Calculation
The purpose of the project is to analyze and monitor the radio signal spectrum wherein its FFT is calculated which is displayed in a graphical LCD.
The method of analyzing the spectrum of an input signal makes use of the Audio Spectrum Monitor project. A frequency conversion procedure is implemented in order to solve the difficulties of directly sampling and analyzing an input RF signal. This is because the acquisition unit must have sufficient speed and accuracy to cover radio frequency range and the number of samples to meet the required resolution is becoming too large. The RF signal is down-converted to lower frequency with a mixer before sampling stage.
The input signal used is an IF signal from radio receiver where an IQ signal is generated by multiplying it with a complex local signal. After filtering out the unwanted frequency components, it is digitized as the AVR does the following processes.
The mixer circuit utilizes two SA612a general purpose DBM ICs as the most significant block in the circuit. The use of SA612A is due to its differential input/output as the output of mixer is used in DC coupling.