Blind standing wave listener

Filter 18.432M

The standing wave ratio monitor circuit shown below is designed for blind amateur radio enthusiasts. The purpose is to enable the blind to check the standing wave ratio of the transmission line according to the sound and adjust the source impedance and load impedance to the fullest possible. match. The thick black lines in the figure are two thin metal strips of 6*70mm which are 1.5mm apart from each other. The inductive reactance of these two strips allows the high-frequency energy of the transmission line to be transmitted to the simple monitor below the figure. The rectified high frequency energy changes the bias voltage at the BG1 base of the transistor such that the resulting sound frequency increases with increasing voltage. According to the original value given in the figure, the sound frequency is about 500H at high frequency signals. According to the rising tone, the transmitter output can be adjusted to the maximum, and the pitch of the tone is gradually reduced, and the world tuner can be adjusted to the minimum standing wave ratio. If you feel harsh when the pitch is raised, you can reduce the pitch by increasing the resistance of 82KΩ.