demodulator

This paper describes the design of a digital I/Q demodulator that will be applied to the PEP-II B factory.

(That's what a modem is: a modulator-demodulator.) So no, you don't interact with a BBS by speech.

Someone should invent some sort of general modulator/demodulator and use sound to connect computers to the Internet!

The 'crude mixer / demodulator' can be done with just one transistor, this just isn't that.

There are even SoCs that integrate a processor and DVB-T demodulator on a single chip, usually used for stuff like set-top boxes.

You just need a software demodulator the catch them, but for sending you'll need an external transmitter (an USB SDR or jack-to-FM).

AM peak detector is probably the easiest and primitive AM demodulator: it's basically made by a diode, a capacitor and a resistance.

You just tune the AM demodulator off center from the FM signal.

A $10 DVB-T demodulator (at scale they can be had much cheaper than that) is a rounding error in the cost of those devices.

Recent advances in high-speed analog-to-digital (ADC) converters allow the I/Q demodulator to be implemented digitally, greatly reducing these systematic errors.

Demodulating FM accurately is much more complicated, but if you'll accept a fairly distorted result then an AM demodulator can be used to demodulate FM.

I remember that in Poland electronic repair shops offered companies removal of the TV demodulator from TV sets used as monitors.

Oops, I read your first comment as saying "CPU, demodulator, AND tuner".

The idea behind this demodulator is quite easy: the diode filters out all of the negative part of the signal, then the positive signal charge the capacitor and the energy is released in a quite constant way (R*C must be several order of magnitude higher than 1/f where f is the carrier frequency) during the negative signal "hole".

"Modem" stands for "modulator-demodulator" and it is there to convert the TCP/IP traffic in your house to some sort of non-TCP/IP connection that goes to your ISP.