KM4OLT - Mike's Ham Home
Radios in technical terms are usually classified by type of conversion it does. They are other classifications but here we're just going to concentrate on conversion type. Here is a list of a few radio types:
A crystal radio could be like below. A simple antenna which could be just a single wire. A diode to detect the amplitude modulation in which the output is audio. Then a set of headphones or ear buds to listen to it. The great thing is the simplicity of it. The down sides are that it's not very selective on what frequency it receives, no amplification, and of course with no amplification the audio is quite faint depending on the signal strength. That is where other components come in handy.
Wikipedia - Crystal Radio
To say that one block diagram will fit all radios is an impossibility. Some contain on pieces of the following diagram while others have multiples or even additional blocks. However this will give you a starting point. This is a Superhet receiver, which in later documents I hope to clarify the meaning in further detail.
Wikipedia - Superheterodyne receiver
As you go throug my site and dig more into each of the components you will begin to understand their function and why some radios have them and some don't.
(c) 2015 Michael R. Monteith