Modulation and Mixing ECE 453

this two-week lab, we were introduced to identify the effects of the analog modulation parameters on the detected audible analog signals, RF signal waveform, and RF spectrum of the signal. Later on, we explored the per ...

this two-week lab, we were introduced to identify the effects of the analog modulation parameters on the detected audible analog signals, RF signal waveform, and RF spectrum of the signal. Later on, we explored the performance of the RF mixer and unwanted mixing products. Same as previous labs, we utilized the signal generators to produce AM and FM signals, and we use MXA and the scope to observe the signal waveforms and spectrums. For the first week, we studied more about AM and FM tone modulation effects and their differences, and the demodulation process. After that, we explored the mixer characterization and the spurious response in the second week. 2. Setups We set up the signal generator with a -20 dBm carrier at 1 MHz and AM modulation, tone frequency of 440 Hz and modulation depth to 20%. For both AM and FM modulation testing, we started by connecting an antenna to the signal generator for audible frequencies, and then connect the signal generator to a scope for signals and MXA for spectrum analyzing. 3. Results I. AM tone Modulation When testing with the audio frequencies, we can hear that the tone goes up as we increase the tone frequency. Also, the volume goes down as we decreased the modulation depth. We set up the signal generator as the original settings, 440 Hz tone frequency and modulation depth of 20%, and the carrier frequency at 1 MHz. Connecting the signal generator to the scope, the carrier frequency did not change, but the peaks are closer (more frequent) as we increase the tone frequency from 440 Hz to 1 kHz. Figure 1 shows the spectrums at tone frequency of 440 Hz and Figure 2 shows the spectrums at tone frequency of 1 kHz. When we increased the modulation depth to 50%, we could observe from the scope that the “envelopes” sides are steeper (sides frequency around peaks are smaller), shown in Figure 3.