Ian Bell wrote:
Phil Allison wrote:
"Ian Bell"
Lastly, the scope is a Rapid Electronics 7020A 20MHz dual channel (which
is a re-branded Pintek) and its -3dB point is quoted as 20Hz.
** Shame how that is just NOT so.
The 7020A has its -3dB point at ** 3.4 Hz ** when in "AC" input coupling
mode.
As is common practice with most scopes, a 47nF 400 volt film cap is placed
in series with the 1 Mohm input to each vertical amplifier :- f -3dB = 1
/ ( 2.pi.C.R)
Here is the schematic for the whole scope.
http://www.rapidonline.com/netalogue/specs/85-2200.pdf
Pity your comprehension skills are so poor. I quoted the manufacturers
spec. Clearly it is conservative. Thanks for the circuit.
Cheers
Ian
My 3 working oscillosopes have ac mode poles at about 3Hz. Having a pole
at 20Hz for ac mode would be substandard indeed.
Patrick Turner.