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The FRS/GMRS - and friends
As can be seen, both services use the same frequency band, mode of operation, and even share some of the exact same frequencies. They differ in the type of user they are targeted at, and the type of usage. One thing that they share, is that neither service was meant for hobby use by radio enthusiasts. Both services are aimed at the non technical user who simply wishes a reliable means of short range communication. There is no license required for FRS, and no test is required for the license for GMRS. This is reflected somewhat in the marketing approach taken by producers of FRS, and GMRS gear. No manufacturer of ham radio gear would damage his credibility by giving estimated range. Radio enthusiasts know that there are too many variables involved to make any such estimates valid. ham operators and other technophiles are interested in radiated power, antenna gain, and other such specifications. Those who are less technically savvy want to know how far they can talk. So advertisers will tell you that there is a range of 5 miles, or 16, miles, or 25 miles, often for gear with the same technical specs.
In many ways this is everything that CB was supposed to be, but never was. FRS radios are very small, cheap, and quite dependable within their limitations. These are great for the kids, or to have sitting in the boat, the glove box, or the back pack. Honest range on these units is a mile at most. In most normal conditions you are talking anywhere from a few hundred feet, to perhaps a block or two. Still, this isn't so bad. Most kids labored under such performance restrictions with their first set of walkie talkies when I was growing. up. For a bit more range and power, there is GMRS.
Like the pure FRS
radios, these are limited to 500mw, and use little rubber antennas. This is why
it is nearly impossible to find any mention of rated power. Instead, these
radios are usually rated by how many miles you are supposed to be able to talk.
This is hype, at the very least. In truth, a CB, putting out five watts, will
far exceed the range of any of these little radios. A recent visit to Cobra's
website reveled a claimed range of 35 miles for a 500mw radio with a no gain
antenna. The site never actually gives the power rating of the radio, but merely
states that it is the maximum legal power. In truth, radios of this type are
rarely able to exceed a mile in range. Also claimed was a 3124 channel
capability - the tone squelch codes being counted as channels. This is so
deceptive that it is hard not to call it a lie. It is also very confusing
(intentionally so) to those who are not radio enthusiasts, and who might wonder
about the 3124 channels, and why most other FRS/GMRS radios only have 22. For
the hundred dollars they are asking for these radios, you could get a commercial
quality radio, from a reputable company that is truthful about its products.
Fifteen channels on twenty three frequencies. Eight duplex, and seven simplex channels are part of the service. These units are allowed considerably more power, up to 50 watts, are allowed to access repeaters for great range, and are capable of duplex operation. A five year, $85 license is required for legal operation of these radios. Unfortunately, as with CB, this requirement is largely being ignored, particularly by hybrid users. GMRS radios may be used for business as well as personal communications, and a license had at one time been granted to corporate entities, for use by employees.
The real draw of these radios is that they offer dependable UHF/FM communications without the requirement of a ham license. This may not seem like a big deal, until you are camping with the kids, or with friends who are not licensed, and want some way to keep everyone in touch. A good quality GMRS radio, or a commercial radio programmed to use GMRS frequencies, can probably get a range of about five miles or so. A good base or repeater, with a good antenna mounted high off the ground should be able to get a range of 15 to 25 miles.
Duplex channels and repeater operation
You may have noted from the list of frequencies above, that GMRS and FRS share seven simplex channels. A simplex channel is one where the transmit and receiver frequencies are the same. For those of us who are not ham radio operators, this is pretty much what we are used to, and how most people consider two way radios to work. The FRS has another seven simplex channels, which are not supposed to be shared with GMRS (though the hybrid GMRS/FRS radios have all of these frequencies). Then there is another set of eight channels which are designated as duplex channels, and are only for use by GMRS.
Duplex channels work the way that a telephone works. You send on one channel and receive on another. Unfortunately, unlike the telephone, you can not talk and listen at the same time. As a matter of fact, you can not talk or listen at all, between a pair of GMRS handhelds using duplex channels. As an example, if two handheld GMRS radios are using designator 550, both will be transmitting on 467.550 Mhz, and both will be listening on 462.550 MHz. So how can they hear each other? Well, they can't. The duplex frequencies are completely useless for point to point communications, unless they access a piece of equipment called a repeater.
Ham and commercial users are quite familiar with repeaters, as are police and fire departments. For the casual radio user, they are an introduction to a whole new way of communicating. A repeater is set up on the exact opposite frequencies of the units with which it communicates. In the example above, a repeater operating on that same channel designator would receive on 467.550 MHz, and transmit on 462.550 MHz - again, just the opposite of the handhelds. What the repeater does is receive on one frequency, and then retransmit on another. So when two radios out in the field are in contact through a duplex channel, both are transmitting to a repeater, and both are receiving each others transmissions through the repeater. Still, the casual user might wonder why you would bother to do this; but it turns out there are some huge advantages to using a repeater.
Though GMRS radios are allowed up to 50 watts of transmit power, such high power would quickly drain the batteries of most handheld radios. Usually a maximum of five watts is used in a handheld, and many radios have power saving settings that transmit at a watt or two. Depending upon the terrain, this may get you five miles, or perhaps a bit more over water, with the little antennas on most handheld radios. A repeater will usually put out the full legal power, and will have a large antenna mounted high off the ground. This antenna will usually produce a certain amount of gain, and its height should allow it to cover an area of many miles. Thus a pair of handhelds operating through a repeater may be able to contact each other over a distance of 20 miles or more.
Repeaters do not indiscriminately rebroadcast everything they hear. This could end up causing a problem with static or some such thing being rebroadcast. What they do is listen for a subaudable tone. Only upon hearing this tone will they rebroadcast. Thus handhelds designed for repeater operation will have tone generators, which are used to open the repeaters.
Though most of us consider FRS/GMRS radios to be typified by the little blister wrapped toys we see at the local discount store, there are many, very good radios available for GMRS, through the reprogramming of PB/PS radios. These are the commercial grade radios that are used in police cars, fire engines, power companies, and by forest rangers and the like. The most popular units are made by Motorola, though Kenwood, G.E., Icom, and others also make such gear. Buying new will cost a fortune; but agencies are always upgrading, and it is possible to get truly magnificent gear, at stunningly low prices. The only downside to this, is that once you use professional quality units, you will be spoiled, and will be ruined for all hobby grade radios.
The other option for a good GMRS radio is the use of hobbyist ham radio gear, modified to work on these frequencies. The 70 cm ham band is very close to the GMRS/FRS bands, being around 440MHz. Many if not most ham radios operating on the 70cm band can be used on FRS/GMRS radio bands. This is done my taking advantage of a radio mod that allows most ham radios to use extended frequencies.
If you are unfamiliar with the wonderful world of radio mods, it is a little bit of the radio underground. The way it works, is that the major radio manufacturers make a dazzling variety of radios, for a number of purposes. Many of these radios share a number of components, often including circuit boards and logic units. In addition, many models of radios are sold in slightly different version, in various parts of the world.
Rather than make countless models of radio for different locations or applications, most companies will create a few basic designs or boards, and then custom configure or program them for various markets. This custom programming often includes the blocking of certain features or frequencies (like the cellular frequencies blocked in scanners designed to be sold in America).
This kind of model flexibility gives ample opportunity for those who know the internals of these radios to turn them into something they were not meant to be. In some cases it is a matter of reprogramming, in others it is the need to change a jumper or cut a diode. In most of today's modern digitally controlled radios, it is often a simple matter of depressing a certain combination of keys simultaneously or in a certain order.
In addition to this, much amateur radio gear is designed to be usable on MARS/CAP frequencies. MARS (Military Auxiliary Radio Service) is a civilian volunteer agency of amateur radio operators set up to assist the military with communications services. This could be for emergency use, use in war, or simply to let soldiers call home. MARS uses extended frequencies just above and below the regular amateur frequencies. CAP (Civil Air Patrol) is an organization of civilian pilots which assists the military in times of need. They have their own set of frequencies which permits them to access the military communications net.
I have put together a fairly elaborate GMRS system of my own. I am a ham operator and have access to radios that can put out hundreds of watts and contact stations all over the world. So why would I bother with GMRS? There are several good reasons. Ham radio gear can only be used by properly qualified (or so we tell ourselves we are) and licensed operators. GMRS can be used by anyone in my family, under my license. In addition, I can talk to anyone using a FRS unit, with no worry about a license at all. I have a couple of brothers who are not ham operators, and a pair of nieces and a nephew who are still kids. Any of them can use my GMRS units and talk to me. None of them can talk to me on any of my ham radios.
My system consists of a mobile, a base, and several handhelds. All of these are former commercial radios, which have been reprogrammed or modified to work on GMRS frequencies. I also have a 70 cm ham radio that I can use on GMRS, but as this is a ham radio, it is strictly for my own use. Though I had thought to pick up one or more classic Motorola commercial radios, I ended up with all Kenwood gear. This was a coincidence, but a strange one, as all of my ham gear is also Kenwood made.
My base antenna is made of copper pipe, and uses a ground plane design. it is mounted approximately 25 feet above the ground. This gives me a theoretical range of about fifteen miles when talking to a similar station, or about seven to nine miles when talking to a hand held. Maximum range for UHF radios is determined largely by antenna height [range in miles = 1.33( square root of height in feet of first station) + 1.33( square root of height in feet of second station) ].
I have to say that this system is everything I want it to be, and is ideal for general communication with friends and family who have no wish to become ham operators. This is a wonderful system for outdoor use, boating, and vacations.
I should also say something about the Multiple Use Radio Service - MURS. This is an often overlooked service with lots of potential. Unlike the UHF GMRS/FRS (similar to the amateur 70 cm band), MURS is a VHF service, similar to the amateur 2 meter service. MURS radios are permitted up to 2 watts of power, and can use antennas which provide gain. The approximate frequency range of MURS is 150Mhz to 155Mhz on five channels. Many 2 meter ham radios are capable of being modified or configured to use the MURS service. Because of its lower frequency, MURS radios have the potential for somewhat better range, and less attenuation.