File:120 MHz Lecher line oscillator 1934.jpg

English: An experimental 120 MHz vacuum tube amateur radio transmitter with a Lecher line tank circuit, built by George W. Shuart, W2AMN, in 1934. During the 1930s research went into extending the frequency of short wave transmitters into the VHF and UHF ranges. The conventional vacuum tube feedback oscillators operated poorly at these high frequencies because of excessive capacitance and inductance of tube electrodes and connecting wires. In this circuit, to address this problem, the type 801 triode tube (bottom) is mounted upside down with the grid and plate terminals connected directly to two parallel 1/4" copper tubes, forming a resonant half-wave transmission line stub (Lecher line) which serves as the tank circuit and feedback path. The interelectrode capacitance of the tube was found to be equivalent to about 1 foot of additional line; that is, the line was found to be 1 foot shorter than a half-wavelength at the oscillation frequency. Mr. Shuart is shown plotting the voltage standing wave on the line. It can be seen that the voltage node is closer to the lower (tube) end, indicating that the tube adds capacitive phase shift. The circuit produced power from 120 to 240 MHz and could be received at 14 miles.

Caption: "The 2.5 meter transmitter, together with the voltage curve along the transmission line"