We love to use versatile GMRS radios when overlanding and camping, and while they do give us the ability to keep in touch over a greater distance than other radios, they do have their limitations. GMRS uses UHF or “ultra high frequency” radio waves , which are basically “line of sight” in the same way light waves are. In order to to know how far they can realistically work, the following analogy might be useful.
The Spotlight Analogy Of GMRS Radio Waves
Some GMRS radios are able to transmit up to 50 watts of power, although you should use this level sparingly. Think of your 5 watt handie-talkie as a small flashlight, and your 50 watt mobile GMRS radio as more powerful spotlight. Your radio will be able to communicate only about as far as you could see either of those lights on a completely dark and clear night, simple as that.
Compared to light, with radio waves, you may only need to have a strong enough “glow” coming over the horizon to be able to communicate, even if you couldn’t see your hypothetical spotlight directly, but you’d still need so “see” something. As with the light from a tall lighthouse, the taller your radio antenna is, and more power your transmit, the better chance it’ll be heard from a distance.
Obviously the more watts of power you transmit, the better chance your signal would be “seen”, but power isn’t everything, and you won’t be able to communicate in areas where there are large obstacles in the signal’s path. If a mountain is in the way for example, no amount of power increase will help.
On the other hand, if there are a few trees between you and the other radio, and some signal is able to get through, boosting power a bit might turn an unreadable signal into one that’s readable. It’s best to always use your radio’s lowest power setting, then increase power if you really need to in a pinch. That way you aren’t adding to congestion on what may be a crowded frequency, across a wide area.
Radio Line of Sight Calculator
Radio line of sight is slightly greater than actual “line of sight”. The formula below is how it’s calculated. An easy RLOS calculator can be found here.
The radio line of sight calculation can help give you some idea what the range of your GMRS setup will be, but it’s not always accurate in the real world, where range may be more or less.
What’s The Real Range Of A GMRS Radio?
Don’t believe any of the ridiculous range claims made by handheld or mobile GMRS radio manufacturers, they simply don’t hold water. To know how far your radio will work, just Imagine that it’s totally dark, and the person in Jeep up ahead – who you want to communicate with – has parked and is looking back in your direction for a signal from your spotlight.
Could they hypothetically see you, or at least a strong glow coming from a light shone in their direction? If so, you could probably communicate by GMRS radio. UHF radio waves are fairly good at squeezing through small spaces and unlike light can travel through things like fabric and thin walls. They may bounce off a canyon wall once or twice, travel through light tree cover and in between houses, but only up to a certain point.
There are many factors which influence GMRS radio range, including antenna height, power output and terrain. The ranges below are a general rule of thumb, and you may experience better or worse performance, depending on your situation.
Our Own GMRS Range
The estimates below are based on the author’s own experience using GMRS radio in a variety of settings. They assume a 5 watt handheld, 50 watt mobile, 5/8 wave mobile antenna with 6 dB gain and 5/8 wave, 6dB gain omnidirectional base antenna at 50′.
- Urban Environment – Around 1/2 – 1 mile from handheld to handheld, up to 2 miles mobile to handheld, and up to 5 miles or more, base to mobile, with base antenna at 50′.
- Rural – Level – Open Country – From 1 to 3 miles, handheld to handheld, up to 5 miles or more mobile to handheld, up to 15 miles or more, mobile to mobile and up to 30 miles base to mobile in very rare cases .
- Rural – Mountains, Hills & Trees – Expect reliable communications only when you can physically see the other vehicle or person.
Exceptions To GMRS Range Limitations
Once every so often, atmospheric conditions may cause your signal to be “ducted” between layers of warm and cold air. When this happens you may think your GMRS radio has developed superpowers. The record for the closest UHF amateur band, 440 MHz, is 2,493 miles. This happens very seldom though, and can’t be relied on for communication. Source: ARRL
GMRS Repeaters, Game Changer For Range
The GMRS range scenarios above are for direct, simplex communication between radios and don’t take into account the fact that there are GMRS repeaters available in many areas. These tend to be located at very high points, such as mountaintops, and are able to provide users with much more range than direct communication. With a repeater, you can talk to another radio that’s not within your line of sight, but which might still be “seen” by the repeater’s antenna. To use a GMRS repeater you’ll need a radio that supports this feature, along with the permission of the repeater owner. For more about repeaters, see MyGMRS.com.
For Extreme Radio Nerds Only:
If you’re wanting to figure out what the range of your GMRS radio is at your exact location, you can try an online radio range calculator called Radio Mobile. This program uses standard radio theory calculations combined with topographic map data to provide an approximation of your expected radio range. This calculator only supports ham frequencies, so 450 MHz can be used instead of 462 MHz. This radio range calculator program is free to use after registering with an email address.
How To Increase The Range Of Your GMRS Radio
There are some simple ways to increase the range of your GMRS radio, but keep in mind, the “line of sight” analogy still holds true, and you can only increase performance up to a certain point.
- Use a longer 1/2 wave antenna on your handheld and a 5/8 wave on your mobile. If your GMRS handheld has a short removable antenna, try switching to a longer 1/2 wave antenna, such as those made by Nagoya which offers a gain of 2.5 dBi
- Use channels 15-22. Increase output power for longer range. (Switch to channels 1-7 or use FRS radios on channels 8-14 for close-range communication.)
- Place a magnetic mount GMRS antenna on the center of your vehicle’s roof, or as close to it as you can.
- When calling another vehicle, wait until you get to a high spot or more “line of sight” location before calling.
- Tune your GMRS antenna to match your radio. For more info, see “How To Tune A GMRS Radio Antenna For Best SWR“
- Don’t starve your radio for power. Use heavy gauge wiring to your vehicle’s battery.
- Ground your radio and antenna for best performance.
- VSWR. Forward and reflected power direct digital readout, without any...
- Maximum measurable power range up to 120W
- Low insertion loss (0.3 decibels or less) structure allows it to be permanently...
- Build in Frequency country. Interface (in and out ): SO239
- Frequency range: 125 - 525MHz.
You can see our article How to Get a GMRS License for more info on how to stay legal.
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