Training/explanation on PL tones

zapman987

Member
Premium Subscriber
Joined
Jan 16, 2014
Messages
290
Location
nc, recently moved to jax, FL
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?
 

n5ims

Member
Joined
Jul 25, 2004
Messages
3,843
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.
 

Saint

Member
Premium Subscriber
Joined
Dec 19, 2002
Messages
3,263
Location
Fort Erie Ontario Canada
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?
This video might answer some questions
 

ElroyJetson

I AM NOT YOUR TECH SUPPPORT.
Joined
Sep 8, 2002
Messages
2,533
Location
DO NOT ASK ME FOR HELP PROGRAMMING YOUR RADIO. NO.
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.
 

AK9R

Lead Wiki Manager
Super Moderator
Joined
Jul 18, 2004
Messages
6,668
Location
Central Indiana
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.
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.
But the radio circuits take the low level PL tone information and uses it in its PL/DPL detector circuits.
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?
 

Kaleier1

Member
Joined
Dec 27, 2019
Messages
227
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 was going to post the exact same thing until I saw your comment. To this day I always think of it that way.
 

dwh367

Member
Joined
Mar 17, 2003
Messages
413
Location
Owensboro, KY (Daviess County)
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.
 

a417

!#
Joined
Mar 14, 2004
Messages
1,937
"Teachers only respond to students who raise their hands in class" or "only let people wearing blue shirts into the club" is how I've heard it explained.
 

ElroyJetson

I AM NOT YOUR TECH SUPPPORT.
Joined
Sep 8, 2002
Messages
2,533
Location
DO NOT ASK ME FOR HELP PROGRAMMING YOUR RADIO. NO.
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.
 
Top