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by cushychicken 729 days ago
In case folks don’t know about the “El Cheapo Special” - you can make very respectable 2GHz passive scope probes with 150ps rise times out of RG-174 coax cable and 1k resistors.

Clip the cable in half, solder the core to the 1k resistor, and the other end of the 1k resistor to the signal you want to probe.

Solder the shield braid to board GND.

50ohm terminate your scope, set probe amplification to 20x, and voila!

Excellent tip recommended both by Paul Horowitz (Art of Electronics) and Howard Johnson (High Speed Digital Design). Works like a charm!
1 comments
0l 729 days ago
The catch however is that this can cause (relatively) high resistive loading, so isn't really suitable for all applications.
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jjoonathan 729 days ago
It really is suitable for most transmission line applications, though, because transmission line impedance is a fixed target. Top-shelf 20-30GHz probes use this exact technique as their "front end" followed by a 50/100 ohm amplifier to lock in the noise figure:

https://www.tek.com/en/datasheet/trimode%28tm%29-probe-famil...

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cushychicken 729 days ago
True - but those are the exceptions, not the rule.

Most modern systems aren’t discrete transistor amplifiers where an arbitrary 1k to gnd will massively affect bias point or circuit operation.

For digital interfaces, or power supplies below ~24V, it’s a great high bandwidth probe option. Much cheaper than active probes too.

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