Wow, lots of antidotal information. How about a simple explanation of the science. When a radio transmits, it emits a signal that can be received by another radio. In most radio receivers there is a circuit called "squelch". This circuit works by requiring a small amount of electrical energy to be present, before the receiving radio's speaker will be turned on. This keeps unwanted static from being heard all the time. Thus, squelch off.....static....squelch on....no static. If a signal is weak, open the squelch and listen to the weak signal. If the signal is strong, increase squelch and this will limit any signals ability to open the receiving radio's speaker....even to the point that it cannot be opened at all.
Now..."Tone and Tone Squelch", add a circuit to the receiving radio that expects a certain sub-audible or digital signal riding along the transmitted radio signal before it will open up the speaker at all. This is what CTSS, PL, DPL, TONE SQUELCH and some other digital signaling circuits do. They set a requirement for that extra signal to be present, before the receiver will open up the speaker.
Now, with that understood, you should not have too much trouble understanding how the transmitter radio works within any variant of this system. The transmitter must be set to emit the required tone, sub-audible tone, or digital signal that a receiver is expecting to hear, in order to enable the receiver's speaker.
So, if I want to transmit using a repeater (which is a receiver coupled to a simultaneously transmitting transmitter) and that repeater's receiver is expecting to hear a particular sub-audible, or digital tone before it will open up it's receiver, then I must set my radio to transmit that tone in order to enable the repeater to hear my signal.
Also, most repeaters transmit tones as well, so I can set my radio to require a particular signal before it will open up and allow me to hear the audio across my radio from the other radio, or repeater. This is good when some repeaters (or any transmitters) are close enough to each other that they occasionally (and un-wantedly) hear each other's transmissions.
This type of tone encoding and decoding, using several, and sometimes multiple different methods gives the user many methods of controlling what they hear on the receiving radio.
Of note, for clarity,I used the word "speaker" above, when in actuality, the limiting circuit can be in many different places within the receiving radio's audio circuit.
Also, please note, there are as many different ways to use these methods as you can imagine......and I have not even touched 'DTMF'
Hope this helps.
Kenny KC4OJS
Sent from my iPad