What is Audio Mixer?Audio mixer or microphone mixer are devices that combines(adds) two or more signals such that the resulting output signal has frequencies of the input signals that were added. Audio mixers are adders, summers or combiners that adds two or more input signals.
An adder circuit example is shown below with two input signals. V1 and V2 are two ac source which produces frequencies 200Hz and 500Hz respectively. They are simply joined by wires. When the voltage across resistor R12 is measured we find that the voltage signal has two frequencies
|Fig: Audio Mixer Circuit example|
The following shows the V1, V2 and Vout voltage signal waveforms. The first is a sinusoid of frequency 200Hz, the second is of frequency 500Hz and the third has both 200Hz and 500Hz component.
The fact that the added signal or the combined signal has both the 200 and 500Hz frequencies can be verified by plotting the Vout signal spectrum.
|Fig: Spectrum of audio mixer output|
As can be seen in the above spectrum of Vout signal it has two frequency components at 200 and 500Hz.
What is RF mixer?RF mixers are devices that multiplies two or more signals such that the output mixed signal has sum and differences of the frequencies of all the input signal frequencies. RF mixers are multipliers and uses non-linear devices such as transistor or diodes.
The following circuit is an example of simple RF mixer. We have two input signals with frequencies 200Hz and 500Hz.
|Fig: RF mixer circuit example|
|Fig: RF mixer signal Waveforms|
In the figure above, the lowest signal waveform is that of the output mixed signal. We can see that it has multiple high and low profiles. This is because of the addition and subtraction of input signal fundamental and harmonic frequencies.
The same information in the frequency domain of the output signal is shown below.
|Fig: Spectrum of RF mixer output|
In the tutorial AM Circuit Design using Proteus you can see example of how RF mixer works.