Wireless Hacks

Hack 9 FRS and GMRS: Super Walkie-Talkies

Use these high powered radios in places where mobile phones just don't cut it.

In the last couple of years, a number of manufacturers have come out with "high power" radios for general use, marketed as family or recreational communication devices and sold as impulse buy items at department stores. They claim a couple of miles range, operate on a chargeable battery pack or AA batteries, and most are surprisingly rugged and simple to use.

The two technologies behind these popular radios are FRS and GMRS. While sold in similar packaging and frequently sitting on shelves right next to each other, these two types of radios are quite different in capabilities and operating rules.

FRS

FRS stands for Family Radio Service , and was approved by the FCC for unlicensed use in 1996. It operates around 462 and 467 MHz, and is sometimes referred to as " UHF Citizens Band." It is not a Part 15 device like 802.11 radios, but is governed by FCC Part 95, Personal Radio Services. FRS radios share some channels with GMRS radios but are restricted to 500mW maximum power. Manufacturers typically claim two miles as the maximum range of FRS radios. FRS radios come with fixed antennas, and cannot be legally modified to accommodate antennas or amplifiers.

FRS channels 1 through 7 overlap with GMRS and can be used to communicate with GMRS radios. If you need to talk only to other FRS radios, use channels 8 through 14 to avoid possible interference with low band GMRS users. See Table 1-1 for the full list of FRS and GMRS frequencies.

GMRS

GMRS stands for General Mobile Radio Service, and is also known as "Class A Citizens Band." Its use is also covered by FCC Part 95, but requires a license to operate. As of this writing, a personal license costs $75 and can be obtained online at http://wireless.fcc.gov/uls/.

Handheld GMRS units can put out up to 5 Watts of power, although 4-Watt handhelds are more common. While fixed-base stations can use up to 15 Watts on most frequencies, they are restricted to 5 Watts when communicating on the FRS channels. Repeater stations are allowed and can transmit as high as 50 Watts. Both fixed-base stations and repeaters can only transmit on the lower "462" frequencies, while handhelds can operate on any GMRS frequency. Again, see Table 1-1 for the full list of FRS and GMRS frequencies. GMRS gear can include removable antennas, making it simple to use a handheld with a car mount or stationary antenna. Combined with the ability to use repeaters, GMRS can be used to communicate over considerable distances.

Table 1-1. FRS and GMRS frequencies

Lower frequency	Upper frequency	Purpose
462.550	467.550	GMRS "550"
462.5625	—	FRS channel 1, GMRS "5625"
462.575	467.575	GMRS "575"
462.5875	—	FRS channel 2, GMRS "5875"
462.600	467.600	GMRS "600"
462.6125	—	FRS channel 3, GMRS "6125"
462.625	467.625	GMRS "625"
462.6375	—	FRS channel 4, GMRS "6375"
462.650	467.650	GMRS "650"
462.6625	—	FRS channel 5, GMRS "6625"
462.675	467.675	GMRS "675"
462.6875	—	FRS channel 6, GMRS "6875"
462.700	467.700	GMRS "700"
462.7125	—	FRS channel 7, GMRS "7125"
462.725	467.725	GMRS "725"
467.5625	—	FRS channel 8
467.5875	—	FRS channel 9
467.6125	—	FRS channel 10
467.6375	—	FRS channel 11
467.6625	—	FRS channel 12
467.6875	—	FRS channel 13
467.7125	—	FRS channel 14

Typically, handheld GMRS units use lower frequencies to communicate with each other when possible, and transmit on the upper frequencies (while listening 5 MHz lower) to talk to a repeater. This allows anyone listening on the "462" side to hear traffic both from handhelds as well as from anyone using the repeater. Always use the lower frequencies and the lowest power settings whenever possible to help avoid unnecessary interference with other GMRS users. Use repeaters only when you can't otherwise establish communications.

Extending Range

While higher power radios can help extend your range a little, the best method for increasing your range is to increase your altitude. UHF radios can reach significantly further when the antenna is high in the air, even with limited power. This is one reason why the Part 95 rules limit "small control stations" to antennas no more than 20 feet higher than the structure to which they are mounted. To make the best use of your FRS or GMRS radio, find high ground when transmitting. In some cases, this can push your available range out many, many miles. If you are using a GMRS radio, attaching it to a tall antenna can significantly improve your effective range.

While these radios are half duplex and allow only limited data transmissions, they are handy in a number of situations. For example, when fine tuning a long distance point-to-point 802.11 link, you may find them far more useful than mobile phones. Any time you are working far away from a city, particularly on hills and mountains, FRS and GMRS radios can work considerably better than a phone. But don't get any bright ideas about connecting a radio to a telephone patch; this is prohibited on both FRS and GMRS.

This writing is by no means authoritative on the labyrinthine FCC rulebook, but should give you an idea of what each technology is good for. If in doubt, see the rules for yourself online at http://www.access.gpo.gov/nara/cfr/waisidx_00/47cfr95_00.html. If you are looking for more information about FRS and GMRS, there is also a wealth of information available from the Personal Radio Steering Group at http://www.provide.net/~prsg/rules.htm.