pl tone question

[ke7vvt]

pl tones

1. They are a continuos part of the transmission right?
2. They are sub-audible (low amplitude), but does that sub-audible tone go through the audio output (speaker) on the receiver?
3. I can test this by transmitting with a pl tone and have a receiver plugged into my computer (via headphone jack) and use my oscilloscope software to check around where the pl tone should be (123MHz)?

 

[Captain Kilowatt]

PL(Private Line) is Motorola's name for CTCSS. It is a continous tone but it is not sub-audible. People often confuse the term sub-audible as being too low in volume when it actually means below the freq which the ear can detect.The tone is injected at about 10 % modulation and in some cases it can be heard from the speaker. Most repeaters do pass the CTCSS ,or PL tone but some may not especially if the higher freq tones are used as it is annoying to hear a 180-250 Hz tone in the background of the audio transmission.:bored:

 

[WX2MIG]

Considering that I'm 52 and suffer from a mild form of industrial deafness, I can't say that I've ever detected the sound of a CTCSS tone on any radio, and that includes both amateur and the VHF radios used at work, and we use tones on our simplex frequencies as well as for our repeaters......

 

[Wire Weasel]

Hi guys,

VVT, yeah QRN is correct....it's low freq. rather than volume. And yes I guess you can observe these tones on an O scope. If not, then a spectrum analyzer.

Good luck

 

[Captain Kilowatt]

Considering that I'm 52 and suffer from a mild form of industrial deafness, I can't say that I've ever detected the sound of a CTCSS tone on any radio, and that includes both amateur and the VHF radios used at work, and we use tones on our simplex frequencies as well as for our repeaters......

I think pretty much all the commercial business band radios filter out the tones now before they reach the speaker but the older units did not. As for amateur gear that is pretty much a hit or miss with most passing the audio. I remember hearing the 250.3 Hz tone on police transmissions over my scanner or 2m radio from the local RCMP repeater when they were still on VHF. Listening to that same repeater on a police radio revealed no such tone so obviously it was filtered out. Some ham gear has a tone search function where you can search for the CTCSS tone being used during a transmission. This only works if the repeater in use actually passes the tone audio.

 

[Radio Tech]

QRN posted good info

Most good controllers do not pass the CTCSS tone. A lot of homebrew repaeaters will.
CTCSS tone deviation is mostly set to around 500 to 800 HZ of FM deviation. When the tone level is higher you can hear a low pitch hum over the transmission.

I use an IRF 1200s or my Motorola Auto tone/DEV to check and set CTCSS tones. But a good deviation meter will show the level.

 

[ke7vvt]

OK thanks. CTCSS/pl tone is in Hz, not MHz. I'll play around with my radio audio jacks and see what I find.

 

[C2]

... yeah QRN is correct....it's low freq. rather than volume.

Hi WW, I think QRN was saying the opposite.

It's low in volume rather than freq.

PL tones range from about 67 Hz to 254 Hz

Most humans can hear down to 20 Hz.

10% modulation would be very low volume, but still detectable in some cases.