Diode Placement for RF (Signal Tracer)

[AngraMelo]

Hello everyone,

Ive built myself a little signal tracer, it is nothing more than an audio amplifier with a probe. I also built a 1kHz oscillator for injecting signal if needed. Many people when building such devices also use a Germanium diode for RF detection.

The thing is that the diode most of the time is used in parallel with the probe as displayed in the picture. This configuration makes no sense to me.

Could anyone please explain to me why is the diode in parallel?

[bob91343]

It's just a rectifier.  One of many possible circuits.  The input capacitor gets charged on the half cycle and then on the other half cycle its voltage is added to the input, a sort of voltage doubler.  At that time, the diode is reversed biased.

[TimFox]

This configuration of the diode rectifier is used when the input capacitor (10 nF) blocks any DC from the probe tip, rectifying the AC component only.
In the other configuration, where the probe tip connects directly to the diode, the rectification depends on the DC level at the tip.