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Signal mixing and oscillator "width"

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LandLack

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Hi to all,
I/we know that in theory mixing is the product between the signal(t) and a cos(wt), and the latter is seen (in frequency domain) as an ideal impulse. Many real world oscillators are so "tight" in frequency that may be seen as an impulse, but I would like to know what are the consequences when we put a "flatter" oscillator signal in the mixer's LO input.
In other words, I would like to know what happens to the output signal when the phase noise is increased. Thank you,

Best Regards,
Badrul
 

The result is that both components, RF and LO are multiplied in a mixer, and the IF input contains the result of this product.
If you need a clean translation of the "high" RF signal in the "low" IF output, use the best LO oscillator you can find. Otherwise by applying a dirty LO you get a dirty IF output.
Oscillator noise problems has bee studied since 1920s.Frequency fluctuations are named phase noise and cause problems in phase modulated signals. Amplitude noise can be suppressed by using balanced mixers.
 

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