CB radio vs. MURS vs. FRS road convoy
In North America and other areas of the world, license-free radio frequency bands used to communicate between vehicles include the 27 MHz CB band and 150 MHz MURS (or Canadian LADD). In the USA, 462 MHz GMRS requires a license to use an external antenna, and license-free FRS is limited to 2 watts with no external antenna allowed per 47 CFR 95.587 (b)1. MURS does allow an external antenna per 47 CFR 95.2741, but the maximum MURS transmit RF power is 2 watts per 47 CFR 95.2767.
In the USA, since the 1970s, CB channel 19 27.185 MHz AM has been a common ground for general communications and calling. For extended conversations, CB 19 users would switch to another channel to avoid tying up the calling channel. For FRS and MURS there generally aren’t enough users in a particular area to expect to get a random response while on the road.
For road convoy use, a radio communications priority is often to avoid annoyance from unwanted users and static while having adequate communication range. An example is charter buses, school field trips, sports groups, off-road vehicles, or other groups that travel together. In the USA the maximum power for FRS is 2 Watts with the antenna built into the radio. While FRS walkie talkies are available for about $15 each, they are not reliable car-to-car for more than about 1/4 mile due to interference and laying the walkie talkie down in the car. This is usually too short for convoy use, say if one person breaks down and the other person didn’t notice immediately, they may drive out of communication range before knowing it.
For CB radio, the maximum transmit power is 4 Watts. A mobile CB radio with FM and CTCSS (Radioddity CB-500) is about $94 currently. For CB mobile antenna, the Cobra HGA 1500, Cobra HGA 1000, K30, or Wilson Lil Wil antenna are each in the $35-$50 price range.
The limit of mobile-to-mobile communication range for CB, MURS, and FRS is primarily in the terrain and interference, not the 2 Watt vs. 4 Watt power. Pick a CB radio convoy channel that is not channel 6, 9, 11, 19, 26, or 28 to avoid interference from high-power users. For MURS, pick any free channel. For CB, MURS, and FRS use a CTCSS tone to avoid hearing other users on the same channel.
- CB radio: choose whether to communicate with truckers or those with inexpensive AM / FM radios.
- CB radio antenna length vs. range in open terrain and clear channel:
- 28-36 inches length is about 3-5 miles.
- 18-24 inches length is about 2-3 miles.
- FRS range is about a half-mile.
- MURS range is about 2-4 miles, but the radios are more expensive.
- GMRS range is about 5-7 miles, but the radios require a license.