Modulation and Demodulation - HF-Probe

When searching for a scheme for a HF probe, I found a good working solution at https://elektronikbasteln.pl7.de/signalverfolger-fuer-nf-und-hf-selbst-gebaut .

The scheme uses two germanium rectifiers and looks like this:

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My hand drawing, a better image can be found on https://elektronikbasteln.pl7.de/signalverfolger-fuer-nf-und-hf-selbst-gebaut

I tried that HP probe schema with good results. The original uses 2 diodes AA118, I have used AA143.

In the next images, we can see a 25 MHz signal, AM-modulated with a 1 KHz signal. This signal is generated by my frequency generator oldie WF PG1 Prüfgenerator.

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On top the 25 MHz signal. Time base is selected to inspect 25 MHz signal curve. The blue signal is the demodulated signal - nothing of interest can be seen at 20ns/section.

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Here I have changed the time base to 100us/section. We can see AM modulation in the 25 MHz signal in yellow curve. We can also see the demodulated 1 KHz signal in blue curve.

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Timebase is now 500us/section. We can see more of the signals.

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I moved the modulation from AM to FM. The HF-Probe can only demodulate AM signals, so we have no visible modulation (yellow curve) and no output signal ( blue curve).

Finally, I moved to a 200 Mhz signal.

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200 MHz signal, AM-modulated with 1 KHz.

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Here I have changed the time base to 500us/section. We can see AM modulation in the 200 MHz signal in yellow curve. We can also see the demodulated 1 KHz signal in blue curve.

The probe schema tested is simple and can demodulate signals in a wide frequency range.