The Hytera HM789 operates across UHFv: 350–470 MHz, 450–527 MHz; VHF1: 136–174 MHz; UHF5: 806–825 MHz (transmit only), 851–870 MHz (transmit and receive), 896–902 MHz (transmit only), 935–941 MHz (transmit and receive). Several band versions exist; which one to buy follows from the frequency assigned to your organisation. UHF passes between walls and obstructions more readily, which is why it is preferred inside buildings, industrial plants and dense urban areas. VHF carries further over open ground and water at the same power. The 700/800 MHz band is used for public safety and specially assigned systems.

RF output power is Low: 1–25 W (136–174 MHz, 350–527 MHz); high: 5–50 W (136–174 MHz), 1–45 W (350–527 MHz); UHF5: 10–35 W (806–825/851–870 MHz), 10–30 W (896–902/935–941 MHz). More power is not automatically better: it extends range and shortens battery life at the same time. Teams working close to a repeater are usually served by the low setting, which also lengthens the shift.

Capacity is 1024 channels across 64 zones. A zone is a page of grouped channels — separate zones are defined for different sites, different shifts or joint working with another organisation. On a multi-site system that grows, this is what lets the channel plan be extended without a rebuild.

Receiver sensitivity is 0.18 μV / BER5%. Sensitivity states how weak a signal the radio can still decode, and a lower number is better. At the edge of coverage it determines range as much as transmit power does — communication usually fails not because the other party cannot hear, but because the radio cannot decode a weak signal.

Ingress protection is IP54. IP67 and above means the device withstands immersion in one metre of water. The rating only holds if the fitted battery and the accessory jack cover carry the same class; a standard battery lowers the protection of the whole assembly.

Operating temperature range is -30°C ~ +60°C.