What happens if you mix two modulated frequencies?

Thread Starter

dcyoung9

Joined Aug 1, 2018
13
My question is: What happens when two modulated rf signals encounter a nonlinear circuit causing the two signals to be mixed (Heterodyning). Say the signals are BOTH 100 KHz. one modulated by a steady 500 Hz signal the other modulated by a 900 Hz.
Would you get back a 400 Hz signal or multple there of? (400,800,1200.1600 etc) (1400 Hz and multiples of 1400 Hz) OR
Would you get nothing with the 100 KHz carrier signals canceling each other out?

Now! what would happen if you left the modulation at 500 Hz and 900 Hz and changed one of the carrier signals to, say 100.020 KHz? (20 Hz higher than the other.)
What would you get back? 20 HZ or what? Modulation???
What would happen to the modulation signals?:oops:
 

Thread Starter

dcyoung9

Joined Aug 1, 2018
13
If the mixer is non linear you get back all the sum and difference frequencies,
n, n + 1, n + 2...... harmonics. And product frequencies -

https://en.wikipedia.org/wiki/Intermodulation

http://www.arcticpeak.com/radiopages/intermodulationproducts.htm

Gosh! Dana, I don't understand why you didn't just give me all the combinations instead of giving me a calculator.... LOL LOL
WOW! For 3 frequencies that is a lot of combinations. I'll have 4 frequencies.
SO, it is just going to treat the modulating frequencies as another frequency.
That makes some sense when you think of it.
Thanks for helping me see it. The calculator is cool. I learned a new term INTERMODULATION.
Never heard of that before. Thanks, Don
Regards, Dana.
 

MisterBill2

Joined Jan 23, 2018
4,564
What happens when a number of modulated frequencies are passed through any nonlinear device is normally called intermodulation. Usually it results in interference and distortion and in general it is undesirable in communications systems because it is interference.Indeed you do get all of the frequencies in varying magnitudes, and it is generally something that we try to prevent.
 
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