I've decided to build up an AM receiver which is intended to capture sound signals from a nearby broadcasting station that is operating at 954 kHz. I've completed the system design and started to test one of the first segments of the receiver which is downconverting the arrived signal of concern into the IF frequency of 455 kHz.
For that conversion, I've utilised a mixer that will use a local oscillator that is based on a PWM signal generator: The PWM signal has a duty cycle of 0.5 and frequency of approximately 470 kHz. That signal is directed into a band-pass filter that has the lower and upper corner frequencies of 1.1 MHz and 1.5 MHz respectively so that the sinusoidal component of approximately 1.4 MHz that is inside that square wave can be obtained and used for downconversion. The relevant sinusoidal frequency component can be seen in the following figure which is the Fourier transform of the PWM signal (Useful info about the frequency component is highlighted with blue colour in the table.).
Of course, that sinusoidal signal is then amplified to a sufficient level for the sake of operation.
I've chosen LM318N for the system and the diagram of the test circuit on Multisim is given below:
And the output signal is as follows:
Obviously, the LO signal is not a pure sine and has deformed amplitude envelope. Could that waveform cause the whole receiver system to fail if it is implemented on real life?