A bit more about CB Radio...
There are three methods of using CB - "mobile" units fitted in vehicles, "base station" setups that usually use a large aerial mounted high to increase range (often up to 10-15 miles), and "handheld" walkie-talkie types you can carry around with you or clip on your belt.
Modern CB's are much smaller than they were, most units are no bigger than a paperback book. They are supplied with a mounting bracket, a fist (hand held) microphone on a tough, curly lead, a red & black power lead for connection to the battery or fusebox and a users instruction manual.
There used to be 240v base CB's made, but currently (April 2007) there are none made, and none are likely to be available in the future, but base operation of a CB is easy enough - just use a Power Supply like this one to run a vehicle CB from the mains.
The handheld CB's are a little larger than mobile phones and run on AA size batteries and have their own aerial. Using rechargeable batteries will save a lot of money if you intend to use a handheld a lot - you can often charge the batteries within the unit so you don't have to constantly take them in and out.
You can use a handheld CB in a vehicle or machine, but the metalwork around you will reduce the range severely. To get round this, there are attachments for the handhelds that slide onto the bottom of the unit, in place of the battery compartment (making the unit a bit smaller), and have a cigar lighter plug with lead for power connection, and an external antenna socket for connecting to a standard roof mounted aerial. Using a handheld in this way will give it the same range as a conventional vehicle-fitted CB.
The main advantage with the hand-held types is that there is a large number of remote microphone/speakers available. There are earphones with small boom mics, clip-on mics, crash helmet sets, combined speaker/mics and even ones that go around your neck and pick up vibrations in your vocal chords - allowing use in very noisy environments. All these can be made to automatically transmit when you start talking, giving you truly hands-free communications. Having said this, for purely machine or vehicle use, i.e. in a tractor, the conventional units are probably going to be easier to use over a period of time.
Local terrain, weather and equipment being used (main aerial size) will affect the range, but the distances given on this page are the sort of ranges you could expect while still maintaining a reasonably clear signal.