Direct-Reading Wattmeters for Use at Radio Frequencies

The principle upon which the operation of direct-reading wattmeters is based has been known for many years. The contribution of this paper lies in the application of this principle to a practical operating instrument for the measurement of high power at radio frequencies. Two instruments are described. The first is useful in the range of frequencies from 500 to 2000 kilocycles. This instrument contains circuits which permit operation at any frequency in this band with no tuning or other change in the instrument. The second instrument operates in the region near 50 megacycles. It is inherently a single-frequency device constructed from sections of transmission lines. The theory of operation is discussed, as well as calibration methods. Test data taken with the instruments with loads having a wide range of power factors are compared with power measurements made on water-cooled loads.