How far will my radio communicate?
The answer is… it depends.
Radio communications range depends greatly upon the local terrain. The flatter the terrain the greater your communications range. Radio waves in the VHF and UHF bands tend to propagate “line of sight”. This means that they will travel in a straight line until they come into contact with an obstacle. This obstacle can be a large hill or mountain, very heavily wooded forests, large metal and concrete buildings, etc. If the obstacle isn’t too large then some of the signal will travel over or around the obstacle and allowing you to communicate.
VHF (MURS, 2 meter ham, etc.) propagates better outdoors. UHF (FRS/GMRS, 440 MHz ham, etc.) propagates better in buildings and urban areas. The shorter wavelength of UHF allows for better penetration into buildings. The longer wavelength of VHF allows for better propagation over small hills and through forests. City police and fire departments tend to use UHF radios and the forestry services tend to use VHF as an example.
Elevating your antenna , whether you operate on the top of a hill or mountain or use an external antenna to raise your radio’s signal above the local obstacles, will increase your communications range. In addition, some antennas offer gain which has the effect of redistributing your radio signal into desired areas giving the effect of transmitting more power. This also can contribute to greater communications range.
Many times you will see radios advertised in department stores claiming 26 mile range. This is a hugely exaggerated claim and is false marketing. While you could obtain this range if both parties were standing on the top of large mountains, this is a very unlikely situation. (All radios will do very well if used on the tops of mountains – remember, elevated antennas from the above paragraph.) In most circumstances, your maximum portable to portable range will be limited to 4-6 miles on flat ground.
If both radio users are standing on flat ground and the local terrain was very flat you would still have to deal with the curvature of the Earth which will be the ultimate limit of range. In the image below, Radio A is in range of Radio B. The two radios are close enough to not have to worry about the curvature of the Earth.
The next image shows two radio users that are far enough apart to be blocked by the curvature of the Earth. Radio signals from Radio A will not reach Radio B.
The final image shows how elevating your radio, either by being on a tall hill or using an elevated external antenna can help overcome curvature of the Earth issues. The radio horizon is increased so that Radios A and B are again within range.
You can calculate the “line of sight” for point-to-point contacts using this online calculator. For example, two radio users holding their portable radios each at 6 feet high would have a maximum range of 6 miles under ideal, flat terrain conditions. Here are some examples from this site:
|Radio A’s antenna height (in feet.)||Radio B’s antenna height (in feet)||Maximum Range Over Very Flat Terrain under Ideal Conditions (in miles)|
As you can see from the above examples how important antenna height can be. Please note that there are other variables that can affect your coverage. The line of sight calculator should not be used as a guarantee of communications range as the numbers are calculated under ideal conditions, not real world ones. You can expect range to be less in most cases.
If you need to determine point-to-point coverage (for example, between you and your friend’s house), check out the HeyWhat’sThat? website. You can run a panorama to see whether you have a strong line of sight signal to a particular location.
Another handy tool is CloudRF. Using this site you can create a computer generated model of your predicted coverage area. If you want to see how much area your radio signal will cover, this tool will generate maps of your coverage area for you. This model can predict fairly accurately the coverage area you can expect but you will need to input more data in order to obtain a coverage map. Some handy templates are available on the site to get you up to speed.
While there are other ways to increase your radio communications range (such as repeaters) you are still at the mercy of your local terrain for direct radio to radio communications (also called simplex). In very hilly wooded terrain ranges can be in the area of 0.5 to 1.5 mile between portable radios. Over water, flat farmland, or in the desert you can expect 3-4 miles or more. Adding a base radio with an external antenna and you can increase your range 1.5 to 3 times depending upon the antenna’s elevation above the ground. Be sure to use a good quality low loss antenna coax cable, waterproof the external connections, and properly ground your antenna system.
Please note: The above was designed to be a reference and not a guarantee of communications range and should only be used as an estimation. No one can accurately guarantee communications range unless a site survey of your area has been completed.