Two Way Radios Guide Part 1
Some people call them ‘walkie-talkies’ or ‘portable radios’ or just plain ‘two way radios’ but what is abundantly clear to me having worked with them for almost ten years now is that there is a lot about them that is not properly understood. In this series I’d like to discuss the various elements of two way radio technology, from the types of radios such as portable, mobile and base, to the latest digital advances that have seen the barriers of two way radio communications broken down dramatically over the past few years as IP networks now allow for inter continental transmission.
Types of two way radio
Portable or hand-held radios are the more traditional type of radio, and most likely what you visualize when you think of a walkie-talkie. This is the more visible type of radio and you will see them being used by emergency service personnel, construction workers and security guards to name but a few. This type of radio is lightweight (normally between 9 and 16 ounces in weight) and can operate on 0.5, 2 or 5 watt power output.
Mobile radios are used in vehicles and run off the battery in the vehicle itself. You will have seen this type of radio in taxis and emergency service vehicles. These units can be programmed to operate up to 25 watts and they transmit and receive their signal via an external aerial, usually placed on the roof of the vehicle.
Base radios are basically the same as mobile radios but are desk mounted, usually on a wedge power supply and plugged directly into ‘house power’. The aerials for these units are installed external to the building on a special RF cable.
Each channel on a two way radio is broadcast on a very specific ‘frequency’. A frequency is measured in megahertz or millions of cycles per second. The inside of a radio contains an oscillating mechanism or electric switch that turns on and turns off at a specific rate – it’s frequency – and when this happens at high speed an electro magnetic field, or radio wave, is created.
Two way radios broadcast in the VHF (very high frequency) or UHF (ultra high frequency) range. VHF has a longer wavelength and is more suitable for outdoor use with less obstruction. UHFs shorter wavelength makes it the better choice for indoor use as it can travel through small openings in a building much better.
In terms of power output (watts) the portable radio has an output of between 0.5 and 5 watts. Commercial two way radios work off 2 or 5 watts and can be programmed to work at either level. Non-commercial ‘walkie-talkies’ that can be purchased at your local electronics store can only operate at 0.5 watts and despite what the salesman will tell won’t work up to 30 miles apart.
The reality of sending a radio signal between two radios is that at some point it will hit an obstruction. The size or type of obstruction will determine how well the signal moves through it. The radios that helped the astronauts that landed on the moon to communicate with NASA were less than 1 watt as there are no obstructions between here and the moon.
A 2 watt radio on flat land will give you approx 1.3 miles range. For every extra watt you will gain an extra 1/3 more in distance. To overcome this limitation you can use a high site location to mount an aerial and send the signal via a third party device called a repeater (more on repeaters in a later post).
(In the next part of this series I will be talking in more detail about repeaters and also how networks are enabling two way radios to cross entire continents.)