This is the single diode circuit. Use it when the diode is super-expensive or the power is "high". The signal is ac-coupled via C3. A 50 Ω termination is ensured by R3. R1 and D2 perform the rectification. The positive peak value is stored in C1. It is slowly discharged by R4 (tbd). Depending on the use of your diode detector, R4 has to be chosen therfore. that the af frequency has low distortion.

The circuit used here. With two diodes, you can create a voltage doubler. This comes in handy, when the signal to be measured is low in amplitude.

For RF rectification a fast switching capability is mandatory. In a p–n diode (e.g. 1N4148), the reverse recovery time can be in the order of several µs to less than 100 ns for fast diodes, and it is mainly limited by the diffusion capacitance caused by minority carriers accumulated in the diffusion region during the conducting state.

Schottky diodes are significantly faster, since they are unipolar devices and their speed is only limited by the junction capacitance. The switching time is approx. 100 ps for the small-signal diodes.

Type	Forw. Volt. [mV]	Capacity [pF]
HP 5082-2800	380	2.0
1N5711	410	2.0
BAT83S	410	1.6
1N5712	550	1.2
HP5082-2811	410	1.2
HP5082-2835	340	1.0

We use the Twin Diode Detector Circuit here. Assembly : R3 = 51 Ω, C3 = 100 nF, R1, R2 = 51 Ω, D1, D2 = 1N5711, C1 = 100 nF, R4 = 10 kΩ, R5 = 51 Ω.



The Engineering Sample, mounted in a SucoBox



Carrier was 1 MHz, + 6 dBm, Amplitude modulated, 40 Hz AF



Output [mV] vs. Input level [dBm]. Useful for "higher" levels.



Output [mV] vs. Frequency [MHz]. Level was 0 dBm (blue) and + 10 dBm (orange).

For a lower level, check out the AD8307 Logarithmic Amplifier
The Levelmod has different sensors as well as an analog output.

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