I am always impressed at how crowded but usable the ISM bands are. Their popularity shows how many users prefer to share a crowded band than to get clear frequencies licensed by the government. Spectrum sharing is a microcosm of the human needs for freedom and for a leviathan to maintain order.
CB radio is an example of the mixed results that come from not regulating a segment of spectrum. The band is a free-for-all of all types of nonsense. In some ways, though, it’s more fun than any other band. Radio used to be an avocation for me, and operating on the CB band brings back some of the feeling of radios being something that had nothing to do with school or work.
CB came about in the late 50s, the FCC re-allocated frequencies in the 27MHz range that had been an orderly amateur radio band to local communication by the general public. 27MHz was a very poor choice for local communication because signals below 30MHz skip off the upper atmosphere, allowing communication over thousands of miles.
The FCC dealt with this issue by saying it was illegal to communicate over 250 km. There were thousands of CB radios in operation around the world at any one time, sharing only 40 channels. The law did nothing to stop the cacophony of noise from hundreds of distant users engaged in local communication. When the band was open for skip, you need to be 20dB over that “ground noise” to be heard clearly. Many people used way more output power than the permitted 4 W, which made the problem even worse.
At some point before I became a radio hobbyist in the mid 80s, the CB band became a complete free-for-all. This condition persists today. Some users transmit thousands of watts and use it mostly for silly contests with other users throughout North America for who has enough power to be heard transmitting over other users. Very foul language is common. 
Channel 9, which is allocated for emergency communication only, has the same level of noise as any other channel because users outside the US do not reserve it for emergencies and many domestic users ignore the rules.
To get away from the crowding, many users use frequencies outside the CB, just above or just below it. There is apparently little enforcement because people talk about it openly.
In the midst of all this lawlessness, CB users are in some ways remarkably orderly:
- Most of the very high power users use channel 6. Lower power users respect that and stay off the channel, resulting in lower background noise on that channel.
- Channel 19 has become the accepted channel for road information. When the band is open for skip, there is more background noise on this channel because it’s widely used. If you are on a US highway and want to find out why traffic is slow or where the police are patrolling, you can get clear helpful information on channel 19.
- People who will go out of the CB band without a second thought seem to be cautious about violating the 10m ham band that begins at 28MHz. The frequencies they squat on just above the CB band are allocated for government use, but the government doesn’t use them. Hams do use the 10m band, and CB users usually respect it.
- Among the 40 legal channels the ones from 30-40 are commonly used for single sideband (SSB) operation. AM operation is common throughout the band, but there is less high-power AM operation on these channels informally allocated for SSB operation.
Because CB channel 19 has a critical mass of users, it’s uniquely useful for getting road information. The fact that it skips and carries thousands of miles makes CB a horrible choice for this, but just like a social networking website its value comes from its critical mass of users. UHF or even a smartphone app would be much more effective, but CB has critical mass.
Before the licensing requirement was dropped for FRS in 1996, small businesses sometimes used CB. This was (and still is) completely legal, and it was a very quick and inexpensive communication system. Sometimes people would broadcast events on CB channels. This was technically illegal, but no one cared.
The lawlessness of the CB band was one thing that motivated me to get my ham license in 1990. Trying to use the CB band for experimentation and real communication is painful. A few years ago, however, it occurred to me that there was some appeal to the fact there’s 1 MHz of spectrum that nobody cares about. 27MHz is too high to be considered an international band but too low to be useful for local communication. It’s just there. You can key down and turn your antenna without asking if the frequency is in use; no one cares. You don’t legally have to identify yourself.
The band sort of reminds of prole neighborhoods of George Orwell’s Nineteen Eighty-Four. The government had become amazingly efficient at spying on its people, but there were huge areas full of working-class people (proles) that the government didn’t feel need to regulate. As a result the low-class areas were in some ways better than the middle class areas.
I romanticize CB but do not hold it as an example of something I would like to see happen to any more of the RF spectrum. If the free-for-all showed signs of expanding, I would support measures to contain it. CB has been a free-for-all all my life. I would be sorry if it ever became another amateur radio band with people identifying with government-issued callsigns using the phonetic alphabet in a Mid-Atlantic accent. It's nice to have about 1.5MHz of spectrum allocated as a free-for-all.
