Understanding Two Way Radio Frequencies
There are two major formats for two-way radios.They are Ultra High Frequency (UHF) radio and Very High Frequency (VHF) radio. Neither frequency band is inherently better than the other.They each have their pluses and minuses. Both formats are effective ways to communicate with another person so deciding on the right radio for you depends on your application.
Two-way radios communicate with each other through use of radio waves. Radio waves have different frequencies, and by tuning a radio receiver to a specific frequency you can pick up a specific signal.
Radio waves are transmitted as a series of cycles, one after the other. You will always see the “Hz” abbreviation used to indicate the frequency of a radio. Hertz is equal to one cycle per second.
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.
You may also hear the term “wavelength” when you hear about radio waves. This term is 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.
While wavelength measures distance between the peaks of cycles, frequency refers to how long the measured time is between the “crest” and “trough” of a wave arriving at the source. So frequency measures time instead of distance, but they are essentially both saying the same thing.
What is significant about wavelength for two-way radios is that it affects transmission range under certain conditions. A longer wavelength as a general rule lets a radio signal travel a greater distance.
Lower frequencies or wavelengths have greater penetrating power. That’s one of the reasons they are used for communicating with submarines. VLF radio waves (3–30 kHz) can penetrate sea water to a depth of approximately 20 meters. So a submarine at shallow depth can use these frequencies.
So from what you read above you may think VHF is always the better choice for a two-way radio no matter where you are using it. That’s not necessarily true. Even though VHF has better penetrating capabilities, that doesn’t necessarily make it the better choice for buildings. Remember the conversation about wavelength above?Wavelength has a big impact on transmission.
To explain this let’s assume we are communicating from one side of a commercial building to the other. In between these two points is a metal wall with a three foot door in it. Metal is an enemy to radio waves and they typically don’t pass through it.
For our example let’s assume that the UHF wavelength the radio uses is about a foot and a half long and a similar VHF radio is around five feet long. These are in the ballpark of their normal wavelengths.
When the UHF transmits its signal the foot and a half long wave will pass through the door since the door is wider than the wavelength. The VHF signal will be totally reflected since it is wider than the opening to the door.
Your microwave oven is an example of this. The glass front door has a metal mesh with very small holes. Microwaves being a very high frequency have wavelengths that are only several inches long. The mesh keeps the microwaves trapped in the oven but it allows you to see inside because light waves have a microscopic wavelength.
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 lots fewer doorways you couldn’t get through.
The one difference 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 more dense 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 as we will talk about in the UHF section below.
In our example above we assumed you had a metal wall with an opening. If you reverse this and 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.
For most applications, lower radio frequencies are better for longer range. A broadcasting TV station illustrates this. A typical VHF station operates at about 100,000 watts and has a coverage radius range of about 60 miles. A UHF station with a 60-mile coverage radius requires transmitting at 3,000,000 watts.
So there is no clear choice for which is better, VHF or UHF. There is a lot of “black magic” to radio technology so it’s not always easy to tell which will work better for your application. To help you decide on the best technology for you, more detail about each one is included below.
To find out more about two way radio frequencies, go to the following address for the free book called Two-Way Radio Success: How to Choose Two-Way Radios,Commercial Intercoms, and Other Wireless Communication Devices For Your Business.
http://www.wirelessintercomsonline.com/downloads/freebook.htm