TWO-WAY RADIO COVERAGE

two way radio coverage
two way radio coverage

One of the most frequent questions people ask when they are looking to purchase two-way radios is how far do they communicate? Or what is their range? This is not straightforward to answer and involves lots of variables to consider.

A brief lesson on radio signal transmission is required to understand the whole range-issue.
Two-way radio transmissions can extend from a couple of hundred metres to a few miles or more, depending on their power output (measured in watts), whether your model uses digital or analogue transmission, the location of the device and the type of frequency you use (VHF or UHF).

Two-way Radio Walkie Talkie Range

The range of your walkie talkie will depend on where you use it – a built-up area reduces the transmitting range of your walkie talkie, whereas a flat, open environment will enable wider transmission.

radio coverage 300x86 - TWO-WAY RADIO COVERAGE
radio coverage

For longer-range transmission, VHF signals between 136 and 174 MHz are recommended, because they are better for reaching greater distances for the same power output. Therefore, VHF is used in maritime radio. However, UHF signals (400 – 470MHz) are better for built-up areas, giving better penetration for the same power. A handheld business-type two-way radio usually broadcasts at 1-5 watts. The more watts a radio has, the farther it can transmit. Increasing the power in watts at the source helps overcome any “resistance” along the way.
Keep in mind that for battery-powered handheld radios more watts is not always a good thing. The higher the wattage, the quicker your batteries run down.

For AM frequencies like those below 2 Megahertz (MHz), the signal follows 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 and intercoms available for you to purchase 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. 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 bounced off surfaces so the straight line between radios, may not always be so straight.

A further factor in determining how far a two-way radio will communicate is the frequency it uses and the environment that frequency is used in. There are two major formats for most two-way radios: Ultra High Frequency (UHF) radio and Very High Frequency (VHF) radio. Neither frequency band is inherently better than the other.  They each have their pros and cons; it depends on the purpose of your communication needs.
Radio waves are transmitted as a series of cycles, one after the other. Hertz is equal to one cycle per second.

wave cycle 300x180 - TWO-WAY RADIO COVERAGE
wave cycle

Radio waves are measured by kilohertz (kHz), which is equal to 1000 cycles per second, or megahertz (MHz), which is equal to 1,000,000 cycles per second–or 1000 kHz. The relationship between these units is like this: 1,000,000 Hertz = 1000 kilohertz = 1 megahertz.

Two Way Radio Wavelength

You may also hear the term ‘wavelength’ from the early days of radio when frequencies were measured in terms of the distance between the peaks of two consecutive cycles of a radio wave instead of the number of cycles per second. Lower frequencies produce a longer wavelength (the width of each cycle gets bigger on lower frequencies).
What is significant about wavelength for two-way radios is that it affects transmission range under certain conditions. A longer wavelength, which corresponds to a lower frequency, as a rule, lets a radio signal travel a greater distance.
Lower frequencies or longer wavelengths also have greater penetrating power. That’s one of the reasons they are used for communicating with submarines. VLF (Very Low Frequency) radio waves (330 kHz) are used to penetrate sea water to a depth of approximately 20 meters.
Even though VHF has better penetrating capabilities and can travel farther, that doesn’t necessarily make it the better choice for use in buildings. Wavelength has a significant impact on transmission distance. Just imagine walking through the building carrying a five-foot-wide pole. You will encounter the same challenges a VHF signal encounters. Now imagine walking through the building with a pole that’s only a foot and a half wide like a UHF wave; there are more doorways you could get through. The one caveat is that wireless signals will penetrate through drywall, masonry, human bodies, furniture, wall paneling, and other solid objects. All these objects will reduce the signal strength though. The denser the object, the more it reduces the signal. VHF will penetrate these obstacles better than UHF, but that doesn’t necessarily mean that VHF is better for indoor applications. you have a three-foot metal object in front of the transmitting radio, then VHF would win. Since the object is three-foot-wide it will totally block the UHF signal whereas the VHF signal will get around it. Lower frequencies such as VHF diffract around large smooth obstacles more easily, and they also travel more easily through brick and stone.
The UHF radio band for commercial radios is between 400 to 512 MHz.  Until recently, it wasn’t widely used.  Now, the UHF radio frequency is used for two-way radios, GPS, Bluetooth, cordless phones, and Wi-Fi.
There are more available channels with UHF so in more populated areas UHF may be less likely to have interference from other systems.  The range of UHF is also not as far as VHF under most conditions, but this reduced range may be a positive in some cases. Since UHF has lower range, there is less chance of distant radios interfering with your signal.

So, there is no obvious choice for which is better, VHF or UHF and many factors to consider in terms of coverage.