InterceptRadio.com Forums

Good evening,
I have noticed that the term "PL Tones" has been used many times in this forum. Not knowing what they are I have been reading about them on the web. The primary thing I see re radio is that people can use them to open Amateur Radio Repeaters. I would presume in these cases the keypad on the radio would issue a tone similar to that of a telephone keypad.
With reference to scanning, how are they used? My feeling is that you would program them similar to a frequency in your radio. Does this then allow you to narrow the scope of received transmissions? As an example, I live in Auburn. If I had a PL tone for the Valley Regional Fire Authority (I still call it Auburn Fire half of the time) would my scanner pick up only calls directed to the VRFA vs. all of Valley Comm? Any explanation/information would be appreciated.
Can PL tones be programed into most scanners? How about the BC245XLT.
Thanks again for your help,
Wayne

_________________
Wayne
KF7FYL

PL tone or Private Line is Motorolas trademark name.

I think G.E. now Ma/Com is Quiet Tone.

Anyway the generic term is CCTSS or Continuous Coded Tone Squelch System. You can see why everyone calls em PL tones. :mrgreen:

What this tone is however is a low "hum" that your transmitter modulates the frequency with during the entire time the PTT is active that is used as a key to open a receiver or receivers on the frequency that are programmed to recognize this PL tone. Most commercial radios filter this out before it gets to the speaker so you wont hear it. My Kenwood TMV-7A passed it quite willingly so was a great tech tool.

The tones keep the lumber yard (tone a) on a community repeater from having to listen to the tow trucks (tone b) on the same repeater.

Keep in mind that the neighboring signal is still there. Just muted. It can still cause interference if the unwanted signal is strong enough. The tow truck driver still has to wait for the lumber yard guy to finish his conversation before trying to talk.

But yes you can use it to keep the other people out of your speaker.

Hope this helps... :D

_________________
"A well regulated breakfast, being necessary to the healthy start of the day, the right of the people to keep and eat food shall not be infringed."

Sounds like you're describing DTMF (Dual Tone Multi Frequency). It's the same as on your phone. There are some ham repeaters that have a phone patch. This means you can use your ham radio as a telephone. To tell the repeater that you need to activate the phone, it's usually necessary to send some tones to the repeater. For example, a user might send #3 to enable the patch.

PL tones are interference reducers. Copying from Wikipedia here:

Simply put, PL tones prevent you from hearing others. It does not prevent others from hearing you.

Many people don't understand this second point. Most of these people are the ones using FRS radios. The "privacy codes" are CTCSS tones. You won't hear anyone else that isn't using the same code, but if anyone within range chooses not to restrict their reciever to any specific PL tone, they'll hear everyone on the same frequency.

There's also DPLs, or DCS (Digital-Coded Squelch). It does the same thing as CTCSS, but works in a different way. Read about it here. Also, read about CTCSS here.

Why would you use it? Let's say two stores in the mall are both using 467.50. If neither used PL tones, they'd both hear the communications from both stores. If store A decided to use a PL tone of 114.8 (both for transmitting and recieving, and on ALL of their radios) then they would only hear their own communications. But store B would still hear A's communications, because their radios are still recieving all signals on 467.5. If store B then programs its radios for PL 100.0, then neither store will hear the other. However, range is greatly reduced if they are both transmitting at the same time (especially if they're in close proximity). Depending on how the radios are programmed (and the repeater if one's being used) users may or may not be able to transmit while someone else is.

I've heard repeaters where two different people are talking at the same time on different tones. I'd never set things up that way, but if you only have a couple frequencies or just 1, sometimes you gotta do what you gotta do.

I think the 245 doesn't do PL tones. I'm not positive, but I bet it would list that feature if it could do it. Check your manual to be sure.

Most of what you have illustrated about tone usage is spot on, however there is no way one repeater could pass audio for two separate conversations, differentiated only by PL. Simplex, sure.

The FM capture effect at the receive site would prevent both signals from being intelligible, allowing only the more powerful to be heard.

Here's a definition:

In telecommunication, the capture effect, or FM capture effect, is a phenomenon associated with FM reception in which only the stronger of two signals at, or near, the same frequency will be demodulated.

The capture effect is defined as the complete suppression of the weaker signal at the receiver limiter (if it has one) where the weaker signal is not amplified, but attenuated. When both signals are nearly equal in strength, or are fading independently, the receiver may switch from one to the other and exhibit picket fencing.

Amplitude Modulation, or AM radio, transmission is not subject to this effect. This is one reason that the aviation industry, and others, have chosen to use AM for communications rather than FM, allowing multiple signals to be broadcast on the same channel.

_________________
Rob
N7LXI - Seattle

N7LXI is correct.

To add to what he said, there are repeaters (Icom FR-4000 for example) that will allow multiple tones on 1 channel & frequency but one group can still only use the repeater at a time. A Busy Transmit Inhibit is programmed in field units to prevent groups from walking on eachother since they can't hear eachother without using a monitor feature to momentarily strip the tone.

_________________
I taste copper.
Comments, views, opinions - and trails of destruction - are my own.

They must have had multiple repeaters then. Unfortunately I can't remember what channel I'm thinking of, but it could be 467.125. I've confirmed WQD410 on this frequency but it's possible there are others using it.

Very true. The old "community repeaters" used this function all the time. Com-Spec made the tone panel in the repeater I used to co-manage.

I found this little blurb on e-ham, referencing to the Com-Spec TP-38 tones panel:

For background, from the 1960s onward in the U.S. commercial land mobile radio service (typically on the 450 - 470 MHz band) multiple customer groups were licensed for and cooperatively used common ("community") repeaters. Every customer group using an individual repeater was assigned a different tone from a group of thirty-eight standard sub-audible CTCSS ("PL") tone codes for their user transmitters, and the steering of a particular repeated transmission into the intended group of user receivers was done on the basis of the repeater's retransmitted tone frequency. Unless their mikes were taken off-hook, the users heard only those repeated transmissions intended for their specific group. The TP-38 facilitated this style of community repeater operation.

_________________
Rob
N7LXI - Seattle

Nothing stupid about you. This thread evolved into a good discussion of how PL tones work, why they're used and different occasions where the implementation of a multiple tone configuration on one repeater would work.

This is one of the reasons I LOVE this message board. Unlike some of the other 2 way and scanner forums I read and participate in, this board has the least amount of ego and chest thumping. (Hear that Batlabs? Hear that Hamsexy?)

It's a great resource for people to share information and knowledge and we all seem to do it without making ourselves seems like jerks. (Well, most of the time, anyway!)

_________________
Rob
N7LXI - Seattle

I think we all scared Gampawayne off... :mrgreen: :mrgreen:


Just to add... radios of the past used reeds to create and decode the pl tones. Radios today use other means and can distinguish tones with much tighter response. Used to be you could false a receiver with a close by tone fairly easily. Nowadays newer radios are programmable and have no problem with adjacent tones...

8)

_________________
"A well regulated breakfast, being necessary to the healthy start of the day, the right of the people to keep and eat food shall not be infringed."

Scared me off, no, not quite but almost. Seriously I appreciate all of your responses. What I did was print them out and read them several times. I even believe I am starting to gain a greater understanding of PL tones.
Can the PL tones be programed into a scanner that has frequencies and talk groups programmed in. I ask, because I was going through the Intercept Data Base for King County and saw no PL tones listed. I looked at other Intercept Data Bases of non-trunked VHF and UHF systems and some of them were listed.
I believe you are correct when you say the BC245XLT will not accomodate PL tones. Everything I have found in my research indicates this is true. I will just have to wait until my next scanner before I can use them.
For those of you who are Ham Radio Operators. If this is an example of what you need to know to become a Ham, I am way out in left field.
Again, many thanks,
Wayne

_________________
Wayne
KF7FYL

Yes, PL Tones and DPL (aka DCS or Digital Code Squelch - Digital style PL tones, not to be confused with digital ANYTHING, we're still talking about analog radios right now) are part of HAM radio as well as land mobile radio in general.

_________________
I taste copper.
Comments, views, opinions - and trails of destruction - are my own.

You are correct in noting that no PL tones are associated with the King co. or val com trunked freqs. They are usually associated with uhf/vhf like you correctly stated. Never a trunked sysytem.