This article is about a cheap transistor mixer,
made on a piece of cardboard.
Step 1: Design the Circuit
I have drawn the circuit in old
Pspice Student student edition software
to save time.
Calculate the input lower frequency limit:
fil = 1 / (2*pi*Ri1*Ci1)
= 1 / (2*pi*3300 ohms*(470*10^-9 F))
= 102.614405604 Hz
Calculate the output lower frequency limit (during shorted output):
fil = 1 / (2*pi*(Rc + Ro)*Co)
= 1 / (2*pi*(3300 ohms + 3300 ohms)*(470*10^-9 F))
= 51.307202802 Hz
Step 2: Simulations
The gains seems to be high in transient simulations plot:
Transient
The frequency response will not be so wide in practise:
Frequency response:
Step 3: Make the Circuit
I chosen this particular layout
(inputs and outputs on the same side) because
of the transistor pin configurations:
The base pin is on the right side of the transistor,
instead of on the left side.
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