How far will my GMRS Two-way Radio transmit?
The most common question from new GMRS Two-way Radio users is: ‘How far will my GMRS Radio transmit?’ and the answer is always the same: ‘It depends.’
There are a wide range of factors that can influence transmission distance of your GMRS Radio in an overlanding vehicle, including but not limited to-
Terrain and Topography
- Hills, mountains, valleys, and urban structures can block or reflect radio signals.
- Flat, open areas allow for longer transmission distances.
Antenna Height & Gain
- Higher gain antennas can dramatically increase potential range in flat, open areas however a high gain antenna will not always be the best choice for all situations.
- Lower gain antennas will not transmit as far as a higher gain antenna but will often perform better in mountainous or hilly terrain due to their radiation pattern.
Radio Power Output
- Mobile GMRS radios are legally allowed up to 50-Watt transmission power, while handheld units or walkie-talkies are limited to 5-Watt transmission power.
- Higher transmission power can mean a greater transmission distance, but only if other conditions are favorable and the other components of the radio system are high-quality and installed correctly.
Obstructions & Buildings
- Dense urban environments reduce range due to signal absorption and reflection.
- Indoors vs outdoors makes a big difference, an important consideration when using a portable radio inside a truck or car.
Weather Conditions
- Rain, fog, and atmospheric conditions can slightly affect signal propagation.
- Temperature inversions can sometimes enhance range unexpectedly.
Radio Type & Quality
- There are a number of differences between the performance of handheld, mobile, and base station units – related both to the maximum transmission power, circuitry design, and most importantly the design and construction of the GMRS antenna.
- Quality of components (e.g. coaxial cable and connectors) is a critical factor in potential transmission distance and overall performance of a GMRS Radio system for overlanding.
Line-of-Sight
- GMRS is line-of-sight; and as a result, the Earth’s curvature limits range unless elevated.
- GMRS Repeaters can extend range by relaying signals over obstacles by utilising Duplex mode on a GMRS Radio.