What really affects radio range?

• Antenna height and location — Raising the antenna even a few metres often beats increasing power. Height above clutter matters more than raw watts for most short-range services.
• Terrain and buildings — Hills, dense urban areas and thick woodland absorb or block UHF (PMR446, FRS) more than lower HF/CB frequencies. CB can sometimes “skip” via the ionosphere; PMR446 almost never does.
• Frequency band — Lower frequencies (CB ~27 MHz) generally travel further around obstacles than UHF (PMR446 ~446 MHz) at the same power, but need larger antennas.
• Power (ERP/EIRP) — Legal limits exist for a reason. Doubling power is only ~3 dB — a noticeable but not dramatic improvement compared with better height or a clearer path.
• Antenna efficiency and type — Licence-exempt PMR446 requires a fixed integral antenna. CB and ham can use better external antennas (within rules). A poor or damaged antenna can ruin performance.
• Repeaters — Common on GMRS and amateur VHF/UHF. They can extend coverage dramatically when both stations can reach the same repeater. Not available on standard licence-exempt PMR446 or UK CB.
• Mobile / cellular coverage (PoC) — Internet PTT depends on data coverage. When the network is down or congested, pure RF still works.

• PMR446 (0.5 W ERP, integral antenna) — Hundreds of metres in a built-up area or dense woodland; 1–3 km in open countryside with good height; more from elevated positions. Not a substitute for a commercial system.
• UK CB (4 W FM, decent vehicle or base antenna) — Local road/farm contacts typically a few to tens of km depending on terrain and antenna. Occasional longer “skip” under good conditions is possible but unreliable.
• Marine VHF — Roughly line-of-sight: height of both antennas is critical. Ship-to-ship often several nautical miles; ship-to-shore depends on the shore station.
• Amateur VHF/UHF with repeater — Can cover large areas of a city or region when both stations access the same repeater.
• Cellular / PoC — Wherever you have usable mobile data (or Wi-Fi). Coverage and latency vary; resilience depends on the network.

Always treat published range figures as best-case under ideal conditions. Test your actual setup in the places you will use it.

• Get the antenna as high and clear as practical.
• Use the correct antenna for the band and keep connectors clean and dry.
• Stay within legal power and equipment rules — modified gear risks interference and enforcement.
• Choose the right service for the job (PMR446 for short site work; CB or amateur for longer rural links; Marine VHF on the water).
• For critical use, plan for the worst case (buildings, weather, battery state) rather than the best advertised figure.