How Does VHF Radio Work?

Line of Sight

• Very high frequency (VHF) radios work on a premise of reception known as line of sight. Line of sight is the ability of the radio to receive signals in a straight line depending on the environment the VHF radio is operating in. There are many things that can affect the VHF radio's ability to receive or transmit signals such as buildings, mountains, hills and other terrain that can keep the radio from sending a signal in a straight line. Mounting your antenna as high as possible such as the highest mast on a boat or standing at the highest point possible in the surrounding terrain will make it easier to surmount the problem line of sight reception and transmission can present.
  
  

Antennas and Types of VHF Radios

• There are two main types of VHF radios to choose from for functionality purposes and they are each slightly different in structure. Fixed mount VHF radios are by name, attached to a static location such as a wall, or dashboard of a ship. These types of VHF radios are generally attached to a power source other than a battery and have the highest transmission and reception capabilities of up to 25 miles. The antenna of a fixed mount VHF radio is attached to the radio by a coaxial cable and as a rule should be at least 3 feet away from the radio to avoid interference such as squeals.
  
  Hand-held VHF radios are a more portable version of the VHF radio that has an antenna attached to hand-held radio itself. These radios are either powered by replaceable or rechargeable batteries and have a dramatically decreased operating range of up to 5 miles. Different types of antennas will yield a varied signal wave pattern measured in decibels. The lower the decibels an antenna have the broader and less concentrated wave patterns it will generate. During transmission which also diminishes the signal strength and reception. In the case of having a lower decibel antenna, it is better to use them in places that allow for higher mounts. As a general rule, the taller an antenna is for a VHF radio, the better transmission and reception capabilities it will produce.
  
  

Reception and Transmission Factors

• The ability of a VHF radio to transmit or receive signals is based on other factors besides line of sight and antennas. First, a transmission channel must be chosen using either a rotary knob (like old car radio knobs) or a keypad dial that uses an up or down button to scroll through each channel. Most radios have a button that will automatically take you to the emergency channel which is usually channel 16 or 9 in some areas. After a channel is chosen a user will be able to send out transmissions by pressing the talk button and speaking into the microphone. VHF radios only receive transmissions from the strongest signal provided in cases when more than one person is talking at once on the same channel. Signal strength is also affected by the amount of transmit power used by the VHF radio measured in watts. Mounted radios can switch their power from 1 watt to a maximum of 25 watts, while hand-held VHF radios generally have a 6-watt transmit limit.