National HRO.M high-frequency communications receiver, 1944

The National HRO was a valve-based (tube) shortwave general coverage communications receiver, manufactured by the National Radio Company (National) in Malden (Massachusetts, USA) from 1935 onwards. The receiver was intended for military and amateur use and became very popular for intercept work during the Second World War. Different versions of the radio were in production until the 1960s.

There are many versions of the HRO receiver and each new production run saw a number of smaller or larger modifications being made to the design. The most well-known versions are arguably the late-war HRO-5 and the pre-war variant the HRO-M, both of which played an important role during the Second World War and both of which are still being used by radio amateursin the late twentieth and early twenty-first century.