3 Dec
2009
3 Dec
'09
7:55 p.m.
On Thu, Dec 03, 2009 at 11:13:05PM +0000, Folderol wrote:
I use the old fashioned method of wiring resistors
directly on
standard glass loaded wafer switches. Initial tests suggest the
bandwidth well exceeds 20kHz - as opposed to less than 1kHz for many
quite expensive commercial units.
They are not so 'standard' today, and probably difficult
to find.
Bandwidth will not be the problem. What you get is a filter
that will boost HF. 1 pf = +3dB at 17.7 Khz on all but the
20 mV range. 10 pf means +3dB at 1.77 kHz, and rising.
A 10M input is more-or-less mandatory in this case,
but anyone else
should feel free to make the ladder impedance whatever they like.
Even a 1M input would require at trimmer across the 0.9M
resistor and fixed Cs for the others.
The only reliable way to have 10M is to use an external
calibrated probe feeding into a standard 1M input (which
then will need a calibrated capacitance as well).
Ciao,
--
FA