Im sure most of you have used 2 way radios with pl tones or Continuous Tone-Coded Squelch System (ctcss), most of the bubble pack radios on the market have these tones as added privacy or to tone the squelch on a repeater. My gmrs handhelds have this option and can even be set for groups in case you need to send messages to only certain people, while the other groups will not get the message.
Many users can be on one frequency without interfering with anyone else.
So anyway, what if fm radio stations used this feature?
For example, on 97.7 fm there could be 3 stations in a 20 mile radius sharing this frequency but all three stations will be using different tones, the listener would choose 97.7 fm and press a scan button that would scan for all stations on 97.7 fm, maybe playing a few seconds of that station before moving to the next station.
It would seem like this would work but on the same token, there is the possibility of interference, so power levels would have to be controlled somehow.
It would be great if this would work, think of all the stations that could share the same channel being more efficient and possibly fitting more stations on the fm dial.
Maybe this idea can be used in some of the low vhf bands like 46 to 49 mhz while fitting many more stations on a small slice of spectrum.
Maybe get rid of IBOC too lol yeah right!
Just one of the many crazy ideas rolling around in my head.
🙂
Tone Squelch
Rock,
I really like the way you think because you ARE thinking and raising great points. Keep it up!
OK. Tone squelch works so that a user on a shared channel doesn’t hear traffic that is not encoded for that particular user but it does nothing to reduce co-channel interference. It only keeps you from hearing traffic not intended for you. It is equivalent to only turning on your radio when you know someone is sending you a message. You will still get co-channel interference if others are transmitting at the same time.
Your idea about using this sort of thing on FM is not without merit and not out of the realm of existing technology. The problem is with analog FM neither the equipment nor the rules permit this, except for HD FM.
Think for a moment about the internet. When you read what I have typed you will see only my message and not those of the thousands of others sharing the same cable connection from here to my ISP nor those millions on the backbone net. This is because my text is tagged with an address label so it only goes to the intended destination. I believe that locally my ISP uses a system derived from what was called the ALOHA network which evolved into the Ethernet, techniques known as time division multiplexing (good google search words). For my message to get through, I still have to have exclusive time on the wire network leaving my house. The magic happens because I am time sharing the ISP and the cable connection with other users. I get just a few microseconds per second to send this. Analog broadcasting cannot work this way since their material is continuous in time. The technology is available but is not used for broadcasting.
There is a whole host of amazing technology available for shared channel communications such as cell phones. Another search word is CDMA.
Perhaps, in line with your comments, we will someday evolve to over the air broadcasting where the signals are separated by tags rather than frequency. It is possible for one transmitter to serve an area with many channels of programming, we are just not there yet for over the air broadcasting. HD FM is already rolled out and is doing this on a limited basis, but this is still essentially frequency division multiplexing.
Hope this gives you some encouragement to keep thinking and moving ahead. This is how innovation happens.
Neil