Intermediate frequency amplifier

[yoamocuy]

Homework Statement

I'm supposed to design and build the intermediate frequency amplifier portion of an am receiver.

Homework Equations

The Attempt at a Solution

I've been looking around online and correct me if I'm wrong but the intermediate frequency amplifier takes an ac signal, filters it, amplifies it, and then goes through that whole process 1 to 2 more times. After looking at some sample circuit designs online it seems that a lot of them use transformers. Is it really necessary to use a transformer? Couldn't I just build a band pass filter and hook that up with a transistor acting as an amplifier?

 

[vk6kro]

Maybe you could, but a conventional amplifier would be easier.

An IF amplifier has to supply most of the gain of a receiver and this gain has to vary with automatic gain control. It also has to supply most of the selectivity of a receiver.

An IF amplifier has to take a signal of, say, 10 microvolts and turn it into a signal of 100 millivolts. This is a gain of 10000.
And you have to make it automatically variable, because a large signal could overload the later individual amplifiers, causing distortion, if you don't.

Op-amp bandpass filters tend to have a tent-shaped response (like an inverted letter V ) where an IF filter should ideally have steeper sides than that.

 

[skeptic2]

IF transformers used to be the way it was done. The time it takes to tune them in a factory is expensive. It is more common nowadays to use ceramic IF filters.