Understanding Privacy Lines, Subchannels & Tones

[marcspaz]

Hey folks.  I have had a small group of people ask me about tones and GMRS/FRS basics in the past week.  I figured I would take one of the conversations here and share it for people new to the service.  Hopefully it will help you understand Private Lines, Privacy Tones, sub-channels, tones and squelching methods, in general.  I am only covering the two most popular in GMRS and FRS, but there are many others available as you move into different radio services and technology. 

 

Before we get into what all that stuff is, lets talk about why it exists.  Per NOAA and the US Census Bureau, the lower 48 states is approximately 3.1 million square miles.  Also, 83% of Americans live on 10% of the total available square miles and 40% of all US citizens live on the east and west coast in counties touching oceans.

 

Following this logic, about 500,000+ licensed and unlicensed operators (estimated by me) are sharing FRS and GMRS radio space, in roughly 310,000 square miles.  So, how does 500,000 people in close proximity, sharing 22 channels, all use their radios at the same time without interfering with each other?  Motorola brings you PL tones!

 

Lets get this out of the way...  regardless of what the manufacturers may tell you or how they label their products, there is no privacy.  Period.  Private Lines (PL), Privacy Tones, Sub-channels and any other name for the same service, does not stop people from hearing you, it stops you from hearing them.  I know... seems like a day in Opposite World, but that's how it works. 

 

I suppose the first thing to do is explain what the PL tones really are, what the more common types are and what each of them do.  A traditional squelch is a signal level squelch.  Meaning, no audio will come out of the speaker until a strong enough signal is received.  Then there are also user squelch types.  With analog radios, the most common type of user squelch uses encoding called Continuous Tone-Coded Squelch System or CTCSS.  This feature is defined as being used to reduce the annoyance of listening to other users on a shared two-way radio channel.  So, as mentioned above, its not that you as a person speaking have any type of privacy, but rather you don't have to listen to everyone on the same frequency.  Hopefully the third time is a charm.

 

Many GMRS and FRS radios only have simple CTCSS functions called Tone Squelch, often displayed as TSQL on the screen when enabled.  This means two things.  One is, regardless of what you do with your squelch knob or set your RF squelch to, no audio will come out of the speaker unless the tone you selected is embedded in the signal you are receiving.  The other thing it does is, when you transmit, what ever tone frequency you have programed gets transmitted with/in your signal to unlock or open the squelch of other radios configured the same way.

 

There is another method of CTCSS called "split tone".  This means that you can use one tone when you transmit and another for your receive.  This comes in handy when repeater owners are trying to limit who can access the repeater, as higher cost radios typically have split tone capability, compared to poorly built and inexpensive radios that would be problematic on a repeater do not.  Also, this makes it a bit more difficult to "discover" the input tone by using scanning tools.

 

Another function of split tone CTCSS is that you can also set your radio to transmit a tone to unlock a repeater or other radio, but leave your receive tone set to null (nothing).  When this mode is enabled, there is typically a display on the radio that either reads TN or TONE.  That means you can bring up a repeater or unlock a radio squelch, but also hear everyone else regardless of what tones they are running, if any at all.  This is actually a great feature for GMRS radios since Repeater Channels share FRS frequencies and GMRS simplex frequencies.  So you can tell if the frequency is in use as well as being able to talk to others who many not be using the repeater.

 

CTCSS is an analog squelching system.  There is also a digital squelching system called Digital-Code Squelch or DCS.  It has similar use cases as CTCSS, but it is sending digitally embedded numeric codes instead of a sub-audible tone.

 

I apologize in advance, but this next portion may get a little confusing.  If you have questions, just ask and myself or one of the other knowledgeable members will be able to help.  All of the numbers below are simply random samples I selected for example.  Last I checked, there are 38 standard tones and an additional 13 expanded tones (not available on every radio) for a total possible 51 tones and 83 DCS codes.

 

Along with the use examples above, you can get creative with DCS, because we are dealing with binary numbers instead of a tone.  You can have the numbers used in a bunch of different combinations.  For example, the number 411 in binary is 00110100 00110001 00110001.  The reverse of this would be 11001011 11001011 11001110.  So we are swapping the meaning of a 1 and a 0.  So the combinations could be as follows:

Normal-Normal = Transmit sends 411 and your radio squelch only opens when it receives 411 in the standard format 00110100 00110001 00110001.

Reverse-Reverse = Transmit sends 411 reversed (or bit swapped) and your radio squelch only opens when it receives 411 reversed, meaning 11001011 11001011 11001110.

Normal-Reverse = Transmit sends 411 standard binary format and your radio squelch only opens when it receives 411 in a reversed binary format.

Reverse-Normal = Transmit sends 411 in a reversed binary format and your radio squelch only opens when it receives 411 in a standard format.

Unfortunately, I am unaware of any radio's that have a DCS option to leave your user squelch open while transmitting a DCS code.  If DCS is enabled, you cannot hear anyone else unless they are using the same DCS number and binary combination.

 

CTCSS tones can also be "reversed".  CTCSS tones, since its analog, we have a phase reversal, often called "reverse burst" when it is only reversed at the end of the transmission.  (Something to Google in your spare time.)

 

On some high-end radios, squelching can get really exotic.  You may be able to create your own custom tone instead of using one of the standard tones.  You may also be able to combine CTCSS tones and DCS codes.  For example:

User-CTCSS = Transmit 2600Hz tone, squelch opens with 2600Hz tone. (random number example)

T-DCS = Transmit 141.3 tone, squelch opens with 411 code.

DCS-T = Transmit 411 code, squelch opens with 141.3 tone.

T-rDCS = Transmit 141.3 tone, squelch opens with 411 bit swapped code.

rDCS-T = Transmit 411 bit swapped code, squelch opens with 141.3 tone.

 

Now, here is the kind of disappointing part.  Some manufactures try to make their equipment sound like something its not.  They will use things like there own custom number code to identify a traditional CTCSS code.  For example, Midland uses code number 22 (also known as a sub-channel) to indicate the tone 141.3.  This makes coordination on tone selection a bit cumbersome between some brands.  It also means that if your radio doesn't display the actual CTCSS tone or DCS code, you need to keep your owner's manual handy for reference. 

 

So... I don't know if that explanation made things better or worse.  LOL  Anyway, some companies use verbiage like "Privacy Tones" which adds to the confusion for some people.  If you are using a true full CTCSS, it just means you are limited to whom you can hear, but everyone can still hear you.

 

The examples I provided above for DCS are not what actually gets transmitted, but rather a conceptual process to help understand at a very basic level of what occurs, simply to understand the difference.  DCS adds a 134.4 bps bitstream to the transmitted audio. To move past concept to the weeds, this video does a great job.

[MichaelLAX]

9 hours ago, marcspaz said:

Unfortunately, I am unaware of any radio's that have a DCS option to leave your user squelch open while transmitting a DCS code.  If DCS is enabled, you cannot hear anyone else unless they are using the same DCS number and binary combination.

Nice summary: If I understand the above comment correctly, my Anytone AT-779UV a/k/a Radioddity DB-20G a/k/a Retevis Ra25 allows for split DCS tones or just a transmit DCS tone and no tone on receive.

[WyoJoe]

4 hours ago, MichaelLAX said:

Nice summary: If I understand the above comment correctly, my Anytone AT-779UV a/k/a Radioddity DB-20G a/k/a Retevis Ra25 allows for split DCS tones or just a transmit DCS tone and no tone on receive.

Michael,

Yes, with that radio you can use split DCS codes, or just a transmit code, or a combination of CTCSS tone on transmit, DCS code on receive, or vice-versa. Basically, you can pick any CTCSS tone or DCS (normal or inverse) code for transmit (or no tone or code at all), and you have the same choices for receive (which does not have to match the transmit tone or code).

As long as the radios at both ends of a conversation are configured to work together and are in range of each other, that should work.

[OldRadioGuy]

There is one situation where PL tones work pretty much like people want them to. 

If I'm on my 2 acres talking with my family on one PL tone and another family a mile down the road is on their 2 acres using a different PL tone on the same channel it will behave pretty much like our two families are on different channels.  The signals within our family groups are strong enough to overwhelm the signals from the other family and the PL tones block us from hearing each other.  

Back when businesses used GMRS/FRS it would work OK.  The gas station and hardware store down the street could have their own conversations without getting all mixed up. 

Of course any listener who turns off their privacy tones will hear everything said on that channel.  So it is only a voluntary privacy.  I always leave the tones off because I want to know if the channel is being used... but we don't live in a busy area.  I suppose turning on XMIT tones only might give you some privacy while allowing you to hear other traffic on the channel.  

Vince

 

[Sshannon]

Marc’s explanation is absolutely excellent and should be pinned.  I learned from it. I would just propose one addition and I apologize to Marc if it’s pedantic.  

Privacy tones do not prevent interference.  If two nearby groups are on the same frequency, but different tones, and one person from each group transmits at the same time, a receiver with receive tones set will lock in on the stronger signal, regardless of tone.  It just won’t reproduce the audio if the tone sent with the stronger signal is incorrect. This could mean that your receiver remains squelched, causing you to miss a transmission that you were intended to receive. 

Another thing to consider is that having receive tones set prevents you from hearing a conversation on the same frequency before you transmit over the top of them.

[MichaelLAX]

Put another way:

You receive a transmission on a specific channel and their tone opens your squelch so you can hear them. 

Now another transmission within your reception zone on that channel commences on a different tone. 

It does not matter that it is a different tone: your squelch is already open and both signals will be received and their distance and transmission power will cause the FM Capture Effect to determine which signal overpowers the other, or, alternatively, causes unintelligible communication between both signals. 

[MichaelLAX]

41 minutes ago, Sshannon said:

Another thing to consider is that having receive tones set prevents you from hearing a conversation on the same frequency before you transmit over the top of them.

My radio lights up white when I am receiving a signal that does not open the squelch due to a different tone. 

[marcspaz]

All great info to add!  Thank you both!

[WROZ250]

For most radio services that are 'shared frequency' the rule is monitor before transmitting.  (although I doubt anyone actively does this anymore, rule or no rule)

On a lot of commercial systems, at least in years past, the microphone hanger would enable a RX coded squelch when hung up, but would be carrier squelch receive when the microphone was removed from the hanger.  Most portables have a monitor button which, when pressed, likewise disables the receiver's coded squelch.

I think the 'big lie' by many manufacturers, is using the term 'privacy'.  Even with CTCSS or DCS, other people can still hear what you are saying and, where GMRS is concerned, the only 'privacy' would be encryption, which is not allowed under  the rules. 

This, encryption, was (apparently) once allowed as my other half has a pair of old Radio Shack 'bubble pack' FRS portables that do have encryption!  I discovered this when checking the radio out one day on a service monitor. 

The point is, and marcspaz did a great job of explaining it, there are sub-audio coding options, CTCSS and DCS (also various forms of paging and select call), to keep your radio silent except for who you want to hear.  This again, is NOT 'privacy'.

 

[mbrun]

So, one of the things to look for in a radio, is one that has a LED/Light that illuminates when the frequency is being used, regardless of whether the party transmitting is using a squelch code and regardless if your radio requires a code to un-squelch.

Of all the radios I own, only the cheap Midland radios do not have the frequency-in-use light. That light prevents the need to manually open squelch to check to see if the frequency is in use. The light tells you it is busy.

Good job Marc.


Michael
WRHS965
KE8PLM

[marcspaz]

@mbrun I love that feature. Some of my radios also light different colors, depending on if the signal is analog or digital  

[gman1971]

1 hour ago, mbrun said:

So, one of the things to look for in a radio, is one that has a LED/Light that illuminates when the frequency is being used, regardless of whether the party transmitting is using a squelch code and regardless if your radio requires a code to un-squelch.

Of all the radios I own, only the cheap Midland radios do not have the frequency-in-use light. That light prevents the need to manually open squelch to check to see if the frequency is in use. The light tells you it is busy.

Good job Marc.


Michael
WRHS965
KE8PLM

This is desired most of the time, I agree.

But not all the time, for commercial stuff sometimes seeing the light go ON when the call in the channel is not for you makes it a bit distracting.

G.

[WROZ250]

18 hours ago, MichaelLAX said:

My radio lights up white when I am receiving a signal that does not open the squelch due to a different tone. 

 

10 hours ago, mbrun said:

So, one of the things to look for in a radio, is one that has a LED/Light that illuminates when the frequency is being used, regardless of whether the party transmitting is using a squelch code and regardless if your radio requires a code to un-squelch.

Of all the radios I own, only the cheap Midland radios do not have the frequency-in-use light. That light prevents the need to manually open squelch to check to see if the frequency is in use. The light tells you it is busy.

Good job Marc.


Michael
WRHS965
KE8PLM

The only downside to that, is that the RX light will also activate on noise and interference.  Any signal that exceeds the basic noise (carrier) squelch setting in the radio.  So depending on the design of the receiver, and/or how extreme the environment, you could find yourself politely waiting to talk because of said noise/interference. 

 

[marcspaz]

That is what the monitor button is for; to confirm the channel is not or is in use and to see if it may be someone you want to talk to, who isn't using the same user squelch you are.

[mbrun]

The only downside to that, is that the RX light will also activate on noise and interference.  Any signal that exceeds the basic noise (carrier) squelch setting in the radio.  So depending on the design of the receiver, and/or how extreme the environment, you could find yourself politely waiting to talk because of said noise/interference. 



 

Agreed. However, I don’t view it as a downside at all. The light’s presence and behavior means I need to use the monitor button far less frequently which improves the overall user experience. If checking the monitor function every single time I wanted to Tx, it would incredibly annoying.


Michael
WRHS965
KE8PLM

[MichaelLAX]

I rarely get noise or interference on my rig unless it is Kevin's jamming of the 725 repeater! 

But I do frequently use the MON(itor) button to pull signals "out of the mud" especially simplex Ham, when I am home and when I am mobile and want to keep listening to someone as I leave their reception zone

[WRPP777]

Hey Marc. Your post got me thinking about my new purchase of my first GMRS radio Wouxun KG-935G. I am new to all this and have a question. Please forgive my ignorance on how all this works. When I do a scan my radio it seems to indicate activity on several channels (blue receive bars on screen). When I go to any of the channels that had activity on them I do not hear anything. Do I need to program my radio in some way to hear anything? If so, what steps do I need to take? Is it code related? Thanks for any help you can give. My users manual is ok but does not go into detail of how to set up the radio. I was thinking that it could listen to any chatter on any channel right out of the box. My error. I would love to have a mentor to help me along. How can I get one and is it possible to email back and forth? New to this forum as well. 

Edited March 8, 2022 by WRPP777
Added text

[OffRoaderX]

10 minutes ago, WRPP777 said:

Do I need to program my radio in some way to hear anything?

No.. 

Unless you (or the factory) have added a RX (Receive) CTCSS or DCS/DPL tone/code.then you dont need to do anything.  Not having a RX code/tone will not prevent you from hearing anything.  HAVING an RX tone/code will prevent you from hearing everything unless the transmission also has that same code/tone..  Remove all RX tones and you will hear everything.

I bet there are some good videos on the Youtubes that explain at all for beginners.

[jc1240]

25 minutes ago, OffRoaderX said:

No.. 

Unless you (or the factory) have added a RX (Receive) CTCSS or DCS/DPL tone/code.then you dont need to do anything.  Not having a RX code/tone will not prevent you from hearing anything.  HAVING an RX tone/code will prevent you from hearing everything unless the transmission also has that same code/tone..  Remove all RX tones and you will hear everything.

I bet there are some good videos on the Youtubes that explain at all for beginners.

The world is a better place with Chris in it.

[marcspaz]

14 hours ago, WRPP777 said:

I would love to have a mentor to help me along. How can I get one and is it possible to email back and forth? 

 

Email is fine and all, but why would you want to limit yourself to a single person? The information and guidance you are looking for is here in this forum. No one person knows everything. However, the shared knowledge and experience of the group is limitless.

 

There are several engineers, technicians and and self-taught operators on here that really know their stuff.  And trust me..  we will call each other out and sort through it, if there is bad information put out there.

 

OffRoaderX gave you a great answer. Take his advice and confirm you don't have receive tones set.

 

Also, if you are in or near a home or building or in a vehicle, you may just be seeing random radio noise (called RF Interference or RFI), tricking you into thinking there is activity. This is especially common near charging bricks/wall warts, computers and 9v cell phones.

[WRPP777]

11 hours ago, marcspaz said:

 

Email is fine and all, but why would you want to limit yourself to a single person? The information and guidance you are looking for is here in this forum. No one person knows everything. However, the shared knowledge and experience of the group is limitless.

 

There are several engineers, technicians and and self-taught operators on here that really know their stuff.  And trust me..  we will call each other out and sort through it, if there is bad information put out there.

 

OffRoaderX gave you a great answer. Take his advice and confirm you don't have receive tones set.

 

Also, if you are in or near a home or building or in a vehicle, you may just be seeing random radio noise (called RF Interference or RFI), tricking you into thinking there is activity. This is especially common near charging bricks/wall warts, computers and 9v cell phones.

Thanks so much for the reply. Good information from everyone on the forum.

 

21 hours ago, OffRoaderX said:

No.. 

Unless you (or the factory) have added a RX (Receive) CTCSS or DCS/DPL tone/code.then you dont need to do anything.  Not having a RX code/tone will not prevent you from hearing anything.  HAVING an RX tone/code will prevent you from hearing everything unless the transmission also has that same code/tone..  Remove all RX tones and you will hear everything.

I bet there are some good videos on the Youtubes that explain at all for beginners.

Thank you for your reply. I'll double check for codes and eliminate them until I need to use them. Have a great day.

[MichaelLAX]

22 hours ago, OffRoaderX said:

Not having a RX code/tone will not prevent you from hearing anything…

I bet there are some good videos on the Youtubes that explain at all for beginners.

I hope those videos don’t repeat these double negatives! 

[marcspaz]

13 hours ago, MichaelLAX said:

I hope those videos don’t repeat these double negatives! 

 

I am pretty sure they don't not have any.

[Sbsyncro]

One thing I'm always curious about - let's say you have 5,000+ people running around in an area of the desert (say, like at TDS in Anza Borrego) and there are dozens of people on every GMRS channel because of how popular GMRS has been made by certain people on the YouTubes.    I and my group use PL tones to not have to listen to everyone. It works GREAT.  

But what does it sound like to all the people that don't know about using tones?  I know they can hear our comms, even though we can't hear theirs.  I assumed that we'd be constantly stepping all over people, and that our comms would also be compromised by people stepping on ours (even though we can't hear them).  But that didn't seem to be the case a couple weekends ago...   It was like we had the free airwaves all to ourselves all weekend...    In this situation, does the "strongest signal win" or something else like radio quality? (I'm using a KG-1000G, so a "good" quality radio and maybe those on Baofengs had more issues...)   If the strongest signal wins, I would have expected a lot more problems with our comms over the weekend, based on the traffic I heard on the same channels but without using tones...   

[marcspaz]

16 minutes ago, Sbsyncro said:

But what does it sound like to all the people that don't know about using tones?

 

To someone with no tones set, it may sound like chaos.  LOL

 

So, a couple of things.  One is, Yes, the strongest signal wins.  If someone is talking to you with a tone, your squelch opens and a second or even third station starts transmitting and your radio hears them at about the same receive strength, because your squelch is open you will hear all signals at the same time.  If the person you want to hear is far away and another station is close by, the close station can cause enough interference that your squelch won't open when the person with the same tone transmits.

 

Bottom line, if you felt like you had the airways to yourselves, then the tech worked.  You were having conversations between conversations.