When you think of a two-way radio, you likely think of a walkie talkie. And unless you work in an industry where you use business two-way radio – such as construction or security – then chances are you might think of toy walkie-talkies and baby monitors.
Thus, you probably think of these are highly crackly and weak devices that aren’t capable of much clarity or range.
But this is the wrong way to think about radio. After all, old-fashioned televisions actually work via radio. This allowed for broadcasting across entire countries, carrying signals with enough detail to render high quality images on the screen!
Bluetooth also uses a form of radio, thereby allowing the transfer of extremely large files between two devices.
In fact, radio is even what SETI is using to try and send signals into space!
So why is it that when you buy a radio to use in place of a Satellite Phone on a mountain adventure, it only has a very limited range?
Factors Affecting Range
Most handheld two-way radios that are available to buy, will fall in the frequency range of 150MHz to 900MHz. These frequencies travel in straight lines, and are unable to travel over the horizon or behind solid obstacles. They can’t travel over the horizon, seeing as the planet is curved and they would fly off into space!
This is unlike AM radio, which allows a user to listen to stations hundreds of miles away. These frequencies below 2MHz are able to travel in circles around the Earth, because they actually get reflected by the Earth’s atmosphere!
How far can a signal travel before it hits the horizon? That actually depends on the height of the mast. The lower to the ground the transmitter, the shorter the distance it will travel – and that is relatively quite low for a handheld Marine VHF Radio for example.
The same thing goes for the height of the receiver – a high mast for instance can sometimes pick up signals that were well on their way into space otherwise.
But this will automatically limit the distance that a two-way system can cover. However, there are also other factors that impact on performance. That includes things like number of trees and other things that might get in the way.
Then there are other forms of interference – like radio jams which can occur if someone is using a two-way radio on the same frequency nearby.
This is actually one reason that radios will use a higher frequency for communication: because an extremely low frequency would be more likely to stick around and cause ‘traffic’ that would interfere with other devices.
So how does all this affect you?
Well, it means that you need to take any advertised range with a pinch of salt. Likewise, it means you may occasionally be able to pick up something interesting if you try using your police scanner from a high vantage point.
Finally, it means that in theory, there are ways to design a radio system for greater range – where the application calls for it.