# How mixer works

#### 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?

#### bertus

Joined Apr 5, 2008
21,897
Hello,

What are you looking for?
Have a look at the two attached PDF's

Bertus

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#### 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.

#### bertus

Joined Apr 5, 2008
21,897
Hello,

Bertus

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#### 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

#### Delta Prime

Joined Nov 15, 2019
1,326
In short they are called harmonics which occur above and below the carrier frequency. As seen above.

#### Man10

Joined Jul 31, 2018
122
Ok, how do i calculate the output frequencies of the mixer?

#### Delta Prime

Joined Nov 15, 2019
1,326
You should try this website but right now I just tried it they're doing maintenance on the site.
http://arrl.org/

#### Delta Prime

Joined Nov 15, 2019
1,326
Ok, how do i calculate the output frequencies of the mixer?
You'll have to pick a particular modulation technique AM FM it goes on and on.

#### Man10

Joined Jul 31, 2018
122
In short they are called harmonics which occur above and below the carrier frequency. As seen above.
So a mixer produces harmonics and 1 of these harmonics equals local oscillator frequency + radio frequency input?

#### Man10

Joined Jul 31, 2018
122
You'll have to pick a particular modulation technique AM FM it goes on and on.
So the output of mixer depends on modulation technique? If i use a different modulation technique and same frequency the output of the mixer will be different?

#### BobTPH

Joined Jun 5, 2013
4,907
Yes, and another is the difference, which is the one used in a superheterodyne receiver.

Bob

#### Delta Prime

Joined Nov 15, 2019
1,326
Hmmm. I am going to have to stand down I no teacher. I leave you in very good hands.

#### 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

#### 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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