While at first glance the schematic for a full radio receiver or transmitter may seem incredibly complex, once you know what you are looking for you can isolate certain parts of the schematic to simplify the process. To understand schematics for radio circuits, you need to be able to isolate these blocks and understand them.
This article aims to simply present the different blocks you will encounter when studying radio circuits. This is just an overview, and the more detailed explanation will be found in the specific chapters and lessons that follow.
The RF spectrum is flooded with radio waves of all frequencies. Filters allow us to cancel out unwanted frequencies, selecting the one we want. Filters at the output of transmitters can reduce harmonics and unwanted noise.
Filters are found in all radio circuits.
Essentially, a radio transforms minuscule amounts of energy found in the atmosphere in the form of EM waves, to a much higher level of power to be eventually fed through a speaker. This requires GAIN, and amplifiers are necessary. To make amplifiers, semiconductors are needed.
A stable frequency generator is needed for a mixer to work. Many topologies exist, and, like amplifiers, endless possibilities abound. From old school LC oscillators to modern DDS frequency synthesizers, many options are available, each having specific advantages and disadvantages.
The heart of any radio system. Demodulators allow us to decode modulated RF signals and transform them into audio frequencies. Likewise, different types of available, depending on which signals we want to demodulate and what performance and complexity we want to work with. Very often, hams use ICs. In the demodulator section, we will build our own from scratch.
Antennas are what catch the EM waves we wish to demodulate and amplify. While easy to understand and build, the theory behind is actually quite complex.