A new method of measurement of resistance and reactance at radio frequencies

A method of measuring the radio-frequency resistance of coils is described. It depends on the change in reactance of a valve-maintained oscillating circuit when it is coupled to the circuit under investigation, and does not require any measurement of current or voltage. Practical details of the working of the method and the construction of the necessary apparatus are given. It is further shown how the method can be applied to the measurement of unknown impedances (e.g. the input impedances of valves, the impedances of aerials, etc.) by associating these impedances in some suitable manner with a coil and measuring the apparent change in the constants of the coil. Measurements have been made at about 10 million cycles per second, but the method could probably be used at higher frequencies than this.