When designing test-gear for physicists / students, you may always want to add some "protection", as you did not write a manual / spec-sheet, because curious researchers anyway connect it first and see what happens. First we used those precious parts from Mini Circuits, but then got curious how those things would work. So this is a design based on things available in our treasure-box (SMS 7621, marking XH2) as well as the insight gained from an autopsy.

This is our broadband (0.2 to 3000 MHz) conectorised limiter version, based on a low cost SMS 7621 (Surface-Mount Mixer and Detector Schottky Diodes by Skyworks). To make it somewhat exclusive, we put it in a suco-box. (approx. € 59. From Huber Suhner). The spectrae below show, that odd harmonics are dominant, i.e. in the time-domain, the signal keeps its sinusodial shape. This makes it interesting for frequency counters as well.

Looks like this circuit can also be used as a Harmonics Generator ...
The input level was + 7 dBm.

This is a broadband smd limiter with a maximal output level of typ. +11.5 dBm. A look inside reveals the design. There are three limiters in series. As we measure about 0.7 Volts in either direction, it is to be assumed, that inside this "black boxes" are two diodes, anti-parallel. They are connected via some nH trace inductance and ac-coupled.

This is a broadband (0.2 to 3000 MHz) smd limiter with a maximal output level of typ. +13 dBm. It is to be assumed, that the design is similiar to the one above.

This is a broadband (3000 MHz) connectorised limiter with a maximal output level of +11 dBm (when a 19 dBm source is connected). The advertising promises protection up to an input level of +30 dBm. A look inside reveals the design. There is one "black box" which likely houses two diodes, anti-parallel. At the input, it is ac-coupled, at the output is a 6 dB attenuator. With a 6 dB attenuator, you may match almost anything to 50 Ω. The silkscreen on the pcb (in, out) does not match the labeling on the case. Maybe ours was assembled on a monday ???

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