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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.