Radio's long wavelength allows it to circumvent obstacles and travel long distances,
unlike visible light and other spectra of higher frequencies. .Of the
various kinds of electromagnetic waves, radio waves have a longer wave
length than infrared rays, and are defined by the Radio Law as
'electromagnetic waves with a frequency of less than 3,000 GHz (3 THz)'.
Frequency refers to how long the measured time is between the "crest"
and "trough" of a wave arriving at the source. Radio waves themselves are not something that humans invented. They have existed since the moment when the universe came into being. The longest radio waves typically encountered by humans are generated using the entire Earth as an antenna. These waves have a wavelength similar to the diameter of Earth. Radio waves are radiated onto the surface of the earth from the sun and the other stars, and electromagnetic waves (radio waves) also arise from movement of the earth's crust and from lightening and so on.
The qualities of radio waves are often compared to those of sound waves, but the definitive difference is that radio waves are transmitted even in the absence of matter (a medium). (For sound waves to be transmitted air is required.) In other words, radio waves can even be transmitted in a vacuum. In fact, radio waves are transmitted from communications satellites.
The shorter the wave length of radio waves becomes, the more they take on the qualities of light, and the greater their straightness becomes. In other words, their energy is concentrated in one direction, and they are said to have strong directivity. Furthermore, the higher the frequency, the more acute is the attenuation of the wave's energy. Therefore, the lowest frequencies are used for communication with submarines, due to their low energy (for stealth) and high penetrating power.
Radio waves with a wavelength of less than around 10 meters are absorbed by the atmosphere. Otherwise, they bounce back and forth between the ionosphere and the ground, making radio ideal for transmitting over the horizon. As of technology has developed, equipment that utilizes radio waves such as television, mobile phones and so on has been introduced, and now radio waves are present all around us.
There are two major formats for two-way radios.
They are Ultra High Frequency (UHF) radio and Very High Frequency (VHF)
radio. Both formats are effective ways to communicate with another
person. There are a number of important factors to consider. These
include where the systems will be used,
how they will be used, and for what purpose or application. Let's go
over the key components of both frequencies to help you decide which
suits your needs better.
VHF signals occupy the low end of the frequency spectrum, from 89.00 MHz to 216.00 MHz. The first wireless transmissions were made from the low frequency band, which has been in constant use ever since. This means that the bandwidth range is abundantly populated.
UHF systems operate in the bandwidth between approximately 450 MHz and 952 MHz. The Federal Communications Commission (FCC) allocated 70 additional channels in 1952 to accommodate the rapid expansion of television in the United States after World War II. UHF bandwidth frequencies are less populated than VHF frequencies.
In simple words, the primary advantage of UHF operation is that there is less chance of interference because of more available frequency spectrum. UHF signals tend to be clearer and are more readily transmitted through metal than VHF signals.
UHF wireless systems always cost more than similar VHF wireless systems. The extra cost of UHF equipment is due to the necessity of using more expensive ultra-high-frequency parts, the greater total number of parts required and the need for more expensive construction techniques.
Battery life for VHF wireless transmitters is almost always better than for similar UHF units. For larger wireless installations, the cost of antennas, cables, antenna splitters and preamplifiers are usually much less for VHF systems and performance is generally better. One disadvantage to VHF equipment can be its size. Since the frequency waves are bigger, an antenna must be bigger.
If the wireless equipment will be used in different cities, VHF systems operating on the special frequencies in the 169-172 MHz range will be a good economical choice (applicable in U.S. and Canada). However, these frequencies, which are sometimes referred to as "traveling frequencies," are very popular, and are not a good choice for situations where large numbers of wireless systems are likely to be present, such as at trade shows and expositions. In such situations, frequency-agile UHF systems will be a better choice.
If you are using your two way radios inside buildings or in a city environment you should always buy UHF since its signal penetrate through walls far better than VHF. If you are only using your radios outdoors (ranching, farming, etc.) then VHF will give you a little more distance.