Build a 10X 100MHz Differential Probe for Signals Embedded in Common-Mode Voltages
This DIY probe features an input impedance of 20MegΩ// 1.25pF, a differential gain of 1/10 V/V, and a common-mode range of ±340V.
Electrical engineer Bud Bennett needed a probe that could grab a 1V differential signal riding on a 60Hz 125VAC mains voltage, but many of the commercial probes available on the market weren’t suitable for that purpose, so he did what any engineer would do in that situation: He created his own for his Rigol DS1102E o-scope.
Bennett designed his 10X 100MHz Differential Probe using a custom PCB, 5V DC adapter to power the probe, and an SMA to BNC pigtail to connect the probe to the scope. He does state that anyone who would like to build his probe should make a few leads for different situations, which use a DuPont 0.1" (2.54mm) 2-pin female connector to attach to the probe.
The 10X 100MHz Differential Probe offers an input impedance of 20MegΩ// 1.25pF-differential (10MegΩ//2.5pF each terminal to GND), a differential gain of 1/10 V/V, and a common-mode range of ±340V (240VAC produces a sine wave 679V peak-peak). It also features a CMRR of >90dB @ DC (~60dB @ 1MHz), a differential voltage range of ±24V for 240VAC common-mode/±24V for 0V common-mode, a bandwidth of 100MHz, and a DC offset of < 20mV.
Bennett reluctantly states that needing a specific tool on a yearly basis doesn’t qualify as a necessity, but he had some downtime waiting on components for a different project and tackled his DIY probe in the meantime. He has uploaded a complete walkthrough of the build (including schematics) on his project page for those interested.