What determines the range of radios?

Understanding Radio Range — Explained Simply

When people buy 2-way radios, one of the first questions is:
“How far will it reach?”

It’s a fair question — but the answer isn’t as simple as reading the number of watts on the box.
Radio range depends on several factors, including power, receiver sensitivity, frequency, terrain, and the type of radio (digital or analogue).
Let’s break it down in plain English.

1. Power (Watts) — Strength, Not Distance

Radio power (measured in watts) tells you how strong the signal is — like how loudly someone is shouting.

A common misunderstanding is that doubling the power doubles the range.
In reality, it doesn’t work that way.

If you double the power, you only gain about 30% more range — not twice as much.
That’s because radio waves spread out as they travel, and most of the extra energy is lost in the air, obstacles, or terrain.

For example:

• A 2.5-watt radio might reach around 5 km in open terrain.

• A 5-watt radio (double the power) might stretch that to about 6.5 km under the same conditions.

So, power helps — but it’s not the magic ingredient people think it is.

In New Zealand, PRS (Public Radio Service) radios are limited to 5 watts of power. Still, they can utilise an external antenna, which can make a significant difference beyond simply increasing power.

2. Receiver Sensitivity — How Well It Listens

Power is about how loudly your radio “shouts”.
Receiver sensitivity is about how well it “listens”.

A radio with good sensitivity can hear weaker signals and maintain communication at greater distances — even when the other radio’s signal isn’t powerful.

For the best range, you want both sides of the conversation to have strong transmit power and sensitive receivers.

3. Frequency — How the Waves Behave

Radios use different frequency bands, and these behave differently in the real world:

• Lower frequencies (like VHF) bend and travel around hills, trees, and obstacles more easily.

• Higher frequencies (such as UHF) are more “line-of-sight,” providing clearer sound but less ability to bend or pass through terrain.

Most PRS radios in New Zealand utilise UHF frequencies, which offer excellent clarity and are particularly effective in open areas, race circuits, or urban environments.

4. Digital Radio (DMR) — Smarter, Not Louder

Digital Mobile Radio (DMR) converts your voice into digital data — a series of 1s and 0s.
This gives several advantages:

• Clearer sound right to the edge of coverage

• Longer battery life

• Better noise rejection

• Ability to rebuild voice when in fringe areas 

The trade-off is that when you move out of range, digital radios stop suddenly — unlike analogue radios, which fade out gradually.

5. Terrain — The Biggest Factor of All

Even with strong power and sensitive receivers, terrain makes the most significant difference.
Hills, buildings, and even thick trees can block or weaken radio signals.

You’ll always get the best range when:

• You have a clear line of sight between radios

• You’re on higher ground

• You use an external antenna to lift the signal higher

In open flat areas, two PRS radios might reach 8–10 km, but in hilly or built-up environments, the same radios might only manage 1–3 km.

In Summary