From wikipedia
Radio modems transfer data wirelessly across a range of up to tens of kilometers.
Using radio modems is a modern way to create Private Radio Networks (PRN). Private radio networks are used in industrial critical applications, when real-time data communication is needed. Also Radio Data Modem enables user to be independent of telecommunication or satellite network operators. In most cases users use licenced frequencies either in UHF or VHF band. Licenced frequency is reserved for gived user in certain area thus ensuring that there is less likelihood to have radio interference from other RF tranmsmitters. Also licence free frequencies are available in most countries, enabling easy implementation, but at the same time other users may use same frequency, thus making it possible that give frequency is blocked. Typical users for Radio Data Modems are: Land survey differential GPS, fleet management applications, SCADA applications (utility distribution networks), automated meter reading (AMR), telemetry applications and many more. Since applications are usually requiring high reliability of data transfer and very high uptime, radio performance plays key role. Factors influencing radio performance are, antenna height and type, sensitivity of radio, output power of radio and complete system design.
