Standing wave monitor for the blind
The VSWR monitor circuit shown in the figure below is specially designed for blind amateurs. Its purpose is to enable the blind to check the VSWR of the transmission line according to the sound, and adjust the source impedance and load impedance to match exactly as much as possible. The thick black lines in the figure are two 6 * 70mm thin metal strips 1.5mm apart from each other. The inductive reactance of these two metal strips enables the high-frequency energy of the transmission line to be transmitted to the simple monitor at the bottom of the figure. The high-frequency energy after rectification changes the bias voltage on the BG1 base of the transistor, which makes the sound frequency increase with the increase of voltage. According to the original value given in the figure, the sound frequency is about 500h at high frequency signal. According to the rising tone, the transmitter output can be adjusted to the maximum, and the gradual decline of more tone can adjust the world tuner to the minimum VSWR. If you feel harsh when the tone rises, you can increase the resistance of 82k Ω to reduce the tone.
Circuit diagram of small monitor
Circuit diagram of telephone monitor