A portable radio direction finder

The Bureau of Standards has just issued a paper by F. W. Dunmore, which describes the development of a portable radio direction finder with but two controls — one for tuning and one for balancing. This direction finder operates over the frequency band from 90 to 7700 kilocycles (3300 to 39 meters). The direction finder is of the simple rotating coil type. The receiving set is of the superheterodyne type, with the controls reduced to one by the use of a cam-operated condenser. The wide frequency range is made possible by a set of seven interchangeable plug-in direction finder coils, each with a corresponding heterodyne generator coil and cam for operating the auxiliary tuning condensers.