How mixer works

Thread Starter

Man10

Joined Jul 31, 2018
122
If L is a local oscillator signal and F is a radio frequency input signal, then the output of a mixer is F - L, F + L and other frequencies, if L and F are inputs to the mixer?
 

Thread Starter

Man10

Joined Jul 31, 2018
122
I have been researching radio engineering. I am just trying to understand what I read. The output of the mixer consist of multiple frequencies.
 

BobTPH

Joined Jun 5, 2013
4,907
Correct. The name mixer is a bit misleading though, it sounds like the two inputs are added, when actually, they must be multiplied.

Bob
 

BobTPH

Joined Jun 5, 2013
4,907
The modulation does not change what the mixer does, to a first approximation, and it is preserved by the mixer, modulating the additional frequencies.

Bob
 

Thread Starter

Man10

Joined Jul 31, 2018
122
So if i use a mixer to downconvert a higher frequency to a lower frequency, the mixer will produce harmonics and i should use a bandpass filter to filter harmonics to separate desired signal from harmonics?
 

Papabravo

Joined Feb 24, 2006
18,426
So a mixer produces harmonics and 1 of these harmonics equals local oscillator frequency + radio frequency input?
What is produced by a "mixer" with the LO frequency l, below the signal frequency f
  1. A signal at the LO frequency l
  2. A signal at the input frequency f
  3. An output at the frequency (f + l), called the Upper Sideband (USB)
  4. An output at the frequency (f - l), called the Lower Sideband (LSB)
The behavior is the result of the multiplication of two sine waves. If you remember your Trigonometry you can work this out for yourself. This is a non-linear operation which is used to produce signals at new frequencies that are different than the frequencies of either input. It is worth noting that both sidebands contain the same information.
 
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