Radios for Airsoft
This is rarely ever the case.
The question you need to ask; how far do they communicate? Unfortunately asking this question is along the lines of asking, “How far is up?”. There are lots of variables involved and no easy, definitive answer. A brief lesson on radio signal transmission is required to understand the whole range issue.
If you are old enough to remember when AM radio was popular you may remember listening to radio stations that were hundreds of miles away. For frequencies like these below 2 Megahertz (MHz), these signals follow the Earth’s curvature because they are reflected off the atmosphere. So AM radio signals in low-noise environments can be received by radios that are way below the horizon hundreds of miles away.
The two-way radios usually fall in the frequency range of 150MHz to 900MHz. Unlike the AM radio waves, radio waves in these frequencies travel in straight lines and as a general rule cannot travel over the horizon or behind solid obstacles.
But as in all general rules, there are exceptions to the rules. Even though these frequencies travel via “line-of-sight” paths, radio signals can travel through many non-metallic objects and be picked up through walls or other obstructions. Even though we can’t see between antennas of a transmitter and receiver, this is still considered line-of-sight to the radios. Also, radio waves can be reflected, or bounce off surfaces so the straight line between radios, may not always be so straight.
“Metal rebar in cement & terrain seriously hampers VHF & UHF. UHF is better in buildings. VHF is better in terrain, (HF NVIS is best).” -Hornsby & Districts Amateur Radio Club, Inc.
Knowing that our radio waves travel in straight lines, then to figure out their maximum range for a two way radio we have to factor in the curvature of the Earth. When you stand on Earth and press the talk button on your radio, the radio waves are going straight and they will eventually just go straight off into space once they pass the horizon. So the distance of the horizon is technically the maximum communication range for a two way radio. But you have to factor in antenna height as well.
To find the line of site distance to the horizon for a given antenna height we can use this formula: horizon in kilometers = 3.569 times the square root of the antenna height in meters.
So if the antenna height of a radio is at 6 feet, or 1.82880 meters tall, the horizon is 4.83 kilometers, or 2.99 miles away, which is Point B in the illustration. Of course this calculation assumes the receiving antenna is laying directly on the ground so raising the height of it would extend line of site.
Point C in the illustration shows another radio with the antenna at 6 foot so theoretically you should be able to communicate almost 6 miles. So realistically, for two people carrying a handheld two-way radio, the maximum communication distance on flat ground with no obstructions is around 4 to 6 miles.
So you may be wondering why you see radios that have range claims of 25 miles or higher. Technically they could communicate that far. Point D on Figure 1 shows a tower sitting on top of a mountain. If you are standing on top of this tower, now your antenna height overcomes a whole lot of the Earth’s curvature and you can communicate much further.
There are other factors that affect the range of a two-way radio too such as weather, exact frequency used, and obstructions. The radio’s power output has a factor too.