Trying to Elmer a newcomer, hes having a hard time understanding PL tones and usage with repeaters. Ive found a few documents out there, but they are a bit technical for him. Any clubs or anyone have any training/documents for newcomers?
Training/explanation on PL tones
- Thread starter zapman987
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nd5y
Member
Maybe the links at the bottom of the wiki article:
wiki.radioreference.com
Continuous Tone-Coded Squelch System - The RadioReference Wiki
wtp
Member
tell him it is a "secret handshake" to do things, like open up a radio...
n5ims
Member
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The easiest way to explain a PL tone is that it basically works as a filter. If that filter (or tone in this case) is active on the receiver, a transmitting station must transmit that tone on its signal to be picked up. If that filter (or tone in this case) is not active, any signal will be picked up no matter if or what tone is being sent.
If you don't have a PL tone set (when you receive) you receive all signals on that frequency (that are in range and have enough signal for your radio to receive them). If you have a PL tone (when you receive) you only receive signals that transmit that tone even if their signal strength are really strong. If a station transmits without a tone or transmits using a different tone, your receiver will not activate so you can hear that station.
If you're attempting to transmit to a station (a repeater for example) that requires a certain tone to be there that station will not hear you if you don't transmit that specific tone. If that station (a repeater for example) does not require a tone, you will get in if you transmit no tone or even if you transmit any tone.
If you don't have a PL tone set (when you receive) you receive all signals on that frequency (that are in range and have enough signal for your radio to receive them). If you have a PL tone (when you receive) you only receive signals that transmit that tone even if their signal strength are really strong. If a station transmits without a tone or transmits using a different tone, your receiver will not activate so you can hear that station.
If you're attempting to transmit to a station (a repeater for example) that requires a certain tone to be there that station will not hear you if you don't transmit that specific tone. If that station (a repeater for example) does not require a tone, you will get in if you transmit no tone or even if you transmit any tone.
Thanks all for the responses. Hopefully they will help him!
Did any of these help him?
ElroyJetson
Getting tired of all the stupidity.
Got a service monitor? In oscilloscope mode, it can be used to show the subaudible CTCSS or DPL tone running below the voice audio level.
It's very instructive to SEE it.
I explain it as this: A low level, low frequency tone is transmitted when you key the radio. Whether you're talking into the microphone or not, that tone is being transmitted. We call it a subaudible tone because It's at a low frequency (under 300 Hz) and at a low level. (700 Hz deviation, or half that if narrowband 2.5 KHz channel spacing is being used) You don't hear that tone in the receiving radio because it's filtered out by the radio filter circuit, and the voice audio without any information under 300 Hz is all you hear. But the radio circuits take the low level PL tone information and uses it in its PL/DPL detector circuits.
It's very instructive to SEE it.
I explain it as this: A low level, low frequency tone is transmitted when you key the radio. Whether you're talking into the microphone or not, that tone is being transmitted. We call it a subaudible tone because It's at a low frequency (under 300 Hz) and at a low level. (700 Hz deviation, or half that if narrowband 2.5 KHz channel spacing is being used) You don't hear that tone in the receiving radio because it's filtered out by the radio filter circuit, and the voice audio without any information under 300 Hz is all you hear. But the radio circuits take the low level PL tone information and uses it in its PL/DPL detector circuits.
Isn't true that the higher frequency CTCSS tones can "leak" through the audio filtering in some receivers? In a perfect world, those filters would be brick walls, but we don't live in a perfect world.
How does the receiver decide whether or not its receiving the correct tone? How does the receiver get from an analog tone to binary logic that opens the squelch?
I was going to post the exact same thing until I saw your comment. To this day I always think of it that way.
ElroyJetson
Getting tired of all the stupidity.
How the PL/DPL decoder is beyond the scope of the original question or my answers. Usually there's a specific IC in the radio that handles those functions, at least in older radios. Newer radios are more integrated. Fewer chips to do more jobs.
dwh367
Amateur Radio Operator
I usually explain it as being like a telephone number. If a repeater has a 103.5 PL then that's it's "phone" number. In order to "call" that repeater one has to set up their radio to "dial" that number (PL) or else it won't answer. That's about as basic as I can make it to the layperson.
k6cpo
Member
Here is what I believe is possibly the best explanation of repeater operation I've ever seen. The portion on PL tones begins on Page 15.
ElroyJetson
Getting tired of all the stupidity.
How does the radio know if it's the right PL tone and how to use it to activate a circuit? The PL decoder is a filter that only the desired tone will make it through. If after the signal is processed, there's a valid tone detected, the detector circuit generates an output signal that opens squelch.
I can't be more specific than that because every radio uses one or another implementation of that concept. Unless you want to get deep into circuit theory for a specific radio, but that'd be well beyond the scope of this discussion.
I can't be more specific than that because every radio uses one or another implementation of that concept. Unless you want to get deep into circuit theory for a specific radio, but that'd be well beyond the scope of this discussion.
The concept of PL tones is pretty simple to understand once it's explained properly. However, considering that bubble pack radio manufacturers market them as "privacy codes" that can muddy the waters and give the uneducated user a screwed up understanding of their purpose.
needairtime
Member
Yes, we need to stop calling them PL tones. PL isn't even private, and it only makes things more confusing. The better name, CTCSS, Continuous Tone Coded Squelch System even helps people understand it. I suppose people should know what squelch is as a base line... then the continuous tone that activates squelch, that makes a lot more sense at least to me!
k6cpo
Member
The term "PL" is a proprietary Motorola name for CTCSS that has come into common usage to the point of becoming a generic term. It's just like Kleenex becoming generic for tissue and Q-Tip becoming generic for cotton swab.
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