English: Lecher line wavemeter, a device used to measure the frequency of radio waves from radio transmitters, from a 1946 radio magazine. Invented in 1888 by Ernst Lecher, it consists of a length of parallel wire transmission line terminated with a shorting bar on a slider that can be slid up and down the line. Radio frequency current was coupled into the line by locating the wire loop (left) near the tank coil of the radio tranmsmitter. RF current flowed in the lines and reflected from the shorted end, creating standing waves of current and voltage along the line. Points of zero current, called nodes, occur every half-wavelength (λ/2) along the line. The nodes can be found by sliding the shorting bar up the line and noting when the RF output current of the transmitter dips. The location of the nodes are noted on the centimeter scale along the line. The wavelength of the radio waves is twice the distance between two successive nodes. The transmitter frequency f can be found from f = c / λ. The frame must be constructed from nonconductive material like wood in order to avoid desturbing the standing waves on the line.

The Lecher line was widely used because it was a way to measure frequency without complicated electronics; this wavemeter could be constructed with simple materials found in any shop. It was used at shortwave frequencies, and particularly at VHF and UHF frequencies which were being explored during the 1930s, until frequency counters became available after World War 2.