Understanding Two-Way Radio Range: The Impact of Frequency, Antenna Height, and Power Output

If you recall the era when AM radio was popular, you might remember tuning into stations hundreds of miles away. This is because frequencies below 2 Megahertz (MHz) can follow the Earth's curvature by reflecting off the atmosphere. In low-noise environments, AM radio signals can be received by radios located well beyond the horizon, hundreds of miles away.

 

Two-Way Radio Power

Another crucial factor affecting the communication range of a two-way radio is its power output, measured in watts. You may have heard FM radio stations claim they broadcast at 50,000 or 100,000 watts. In contrast, a handheld business-type two-way radio typically broadcasts at 1-5 watts, while a vehicle mobile radio may broadcast anywhere from 5 to 100 watts. The higher the wattage, the farther the radio can transmit.

Why is this the case? Similar to how water loses pressure as it moves through a pipe or how electricity loses power as it flows along a wire, radio waves also experience signal loss due to the laws of physics. Increasing the power output in watts at the source helps to overcome this signal loss and extend the transmission range.

However, for battery-powered handheld radios, more wattage is not always beneficial. Higher wattage results in faster battery drain. Therefore, it's essential to balance power output and battery life for optimal performance.

Radio Frequencies

Another important factor in determining the communication range of a two-way radio is the frequency it uses and the environment in which it operates.

Two major frequency bands are commonly used in two-way radios: Ultra High Frequency (UHF) and Very High Frequency (VHF). Neither frequency band is inherently better than the other; each has its advantages and disadvantages. Choosing the right radio depends on your specific application.

Two-way radios communicate via radio waves, which come in different frequencies. By tuning a radio receiver to a specific frequency, you can pick up a particular signal. Radio waves are transmitted in cycles, and frequency is indicated by the abbreviation "Hz," which stands for Hertz, or cycles per second.

Radio frequencies are often measured in kilohertz (kHz), equal to 1,000 cycles per second, or megahertz (MHz), equal to 1,000,000 cycles per second. The relationship is as follows: 1,000,000 Hertz = 1,000 kilohertz = 1 megahertz.

You might also encounter the term "wavelength" when discussing radio waves. This term dates back to when frequencies were measured by the distance between the peaks of two consecutive cycles of a radio wave rather than the number of cycles per second. Lower frequencies produce longer wavelengths.

Wavelength is significant for two-way radios because it affects transmission range under certain conditions. Lower frequencies, which correspond to longer wavelengths, generally allow a radio signal to travel farther.

Lower frequencies or longer wavelengths also have greater penetrating power, which is why they are used for communicating with submarines. Very Low Frequency (VLF) radio waves (around 330 kHz) can penetrate sea water to a depth of approximately 20 meters, allowing submarines at shallow depths to use these frequencies.

Given this information, you might think VHF is always the better choice for a two-way radio due to its lower frequency and greater signal travel distance. However, this isn't necessarily true. While VHF has better penetrating capabilities and can travel farther, it may not be the best choice for use inside buildings.

For example, consider communicating from one side of a metal commercial building to the other, with a metal wall and a three-foot doorway in between. Metal is a barrier to radio waves, which typically don't pass through it.

Assume a UHF radio wavelength is about a foot and a half wide, while a VHF radio wavelength is around five feet wide. In this scenario, the UHF signal, with its narrower wavelength, can pass through the door, while the VHF signal, being wider than the doorway, will be reflected.

Your microwave oven provides an illustrative example. The glass door has a metal mesh with small holes. Microwaves, which have wavelengths only several inches long, are kept inside by the mesh, but you can still see inside because light waves have microscopic wavelengths.

Imagine walking through the building with a five-foot-wide pole (like a VHF wave) versus a foot-and-a-half-wide pole (like a UHF wave). The narrower pole will encounter fewer obstacles.

Wireless signals can penetrate materials like drywall, masonry, human bodies, furniture, and wall paneling, but these objects will reduce signal strength. Denser objects reduce the signal more. While VHF penetrates these obstacles better than UHF, it doesn't necessarily make VHF the best choice for indoor use.

In another scenario, if you have a three-foot-wide metal object in front of the transmitting radio, VHF would be more effective. The VHF signal can diffract around the object, while the UHF signal would be blocked. Lower frequencies like VHF can more easily navigate around large obstacles and through materials like brick and stone.

For most applications, lower radio frequencies are better for longer-range communication. For example, a typical VHF TV station operates at about 100,000 watts and has a coverage radius of around 60 miles. A UHF station requires 3,000,000 watts to achieve the same range.

There is no clear answer as to whether VHF or UHF is better. Radio technology involves many variables, and the best choice depends on your specific needs. More detailed information about each technology is provided below to help you make an informed decision.

The UHF radio band for commercial radios operates between 400 to 512 MHz. While not widely used until recently, UHF frequencies are now common in two-way radios, GPS, Bluetooth, cordless phones, and Wi-Fi.

UHF offers more available channels, which is advantageous in populated areas where interference from other systems is more likely. Although UHF typically has a shorter range than VHF under most conditions, this reduced range can be beneficial by minimizing interference from distant radios.

While VHF may penetrate physical barriers like walls more effectively, it doesn't necessarily provide better coverage inside buildings. The shorter wavelength of UHF allows it to navigate through more spaces within a building. For example, a UHF signal can pass through a small doorway, while a VHF signal might be blocked.

Comparison of Indoor Range

Here is an excerpt from a brochure by a leading two-way radio manufacturer, illustrating the predicted range of their handheld VHF and UHF radios:

"Coverage estimates: At full power, line-of-sight, no obstructions, the range is approximately 4+ miles. Indoor coverage at VHF is approximately 270,000 sq ft and 300,000 sq ft at UHF. Expect about 20 floors of vertical coverage at VHF and up to 30 floors at UHF. Note: Range and coverage are estimates and are not guaranteed."

The longer wavelength of VHF makes it harder for the signal to bounce through walls, buildings, and rugged landscapes, reducing its range in such environments. However, this may not be an issue if the required range is only a few hundred feet. An external antenna can be added to a VHF base station to mitigate some of these problems.

One downside to UHF is the requirement for an FCC license to operate on these frequencies, although many VHF business band frequencies also require a license. However, radios operating in the VHF MURS (Multi-Use Radio Service) frequencies do not require a license.

Another advantage of UHF's shorter wavelength is that the antenna can be shorter than an equivalent VHF radio, making it more convenient for portable use. Manufacturers often design shorter antennas for their VHF portable radios as well.

VHF Radio

VHF is used for FM radio, two-way radios, and television broadcasts, with the commercial radio band spanning 130 - 174 MHz.

Both UHF and VHF radios are subject to line-of-sight limitations, but VHF is slightly more affected. While VHF waves can penetrate trees and rugged landscapes, UHF frequencies tend to perform better in these conditions. However, in open areas without barriers, VHF waves can travel almost twice as far as UHF waves, making VHF ideal for long-range outdoor communication.

For outdoor use, VHF radios are typically the best choice, especially when using an indoor base station with an external antenna. The higher the antenna is placed, the farther the transmission range. However, in heavily wooded areas, UHF radios may transmit better through the trees.

The FCC opened the MURS spectrum for two-way radio use, which operates in the VHF 150 MHz band. MURS offers 5 channels with 38 privacy codes each, allowing users to only pick up conversations from radios transmitting their code. No license is required for MURS products.

With MURS, you can enhance range by adding an external antenna, which can be mounted on a building or tower. Some manufacturers claim an external antenna can increase the effective radiated power by a factor of four, enabling MURS intercoms to transmit several miles, depending on terrain and antenna height (up to 60 feet above ground).

Summary

If you primarily use your two-way radios inside buildings, UHF is likely the best choice. However, VHF can still be effective in many applications where the transmission distance is short. For outdoor communication, VHF is generally better unless the area is heavily wooded or has many buildings obstructing the signal.

Both UHF and VHF technologies can work well for short-range communication. For more extensive coverage, repeaters can relay UHF signals, though this setup is typically complex. Many cities offer repeater services for a monthly fee. For most applications, VHF or UHF radios alone will suffice.
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