It's common to recommend a Schottky as a replacement for the 1N34A.
I've done it myself. That's why I was surprised to find this web page -
http://www.cliftonlaboratories.com/diode_vf_vs_if.htm
where this guy discovers that the Schottky diode (1N5711, to be
specific) can show some pretty high forward voltage drops. Turns out
that the low drop we're all familiar with exists at quite low values of
forward current -- less than 1 mA. At ~2 mA is a sort of breakpoint
where Vf begins to increase at a faster rate than in the silicon or the
germanium diodes. By ~10 mA, the 1N5711 has the highest forward voltage
of all three. Quite an eye-opener!
You might think that for the RF probe application, forward current will
be small. Maybe it is. But often times small average currents are
misleading if there's a short conduction angle (time).
72--Nick, WA5BDU
--back to counting screws
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