[sdiy] filter response on a scope

[Scott Juskiw]

Use XY mode on your scope. Y is driven by a sawtooth wave (upward ramp) that also controls an oscillator's pitch. Feed the oscillator (sine wave output) into your filter's audio input. X is driven by the output from your filter. Set the filter cutoff frequency as appropriate to get a nice display.

On 2010-10-17, at 2:02 PM, David G. Dixon wrote:

> Hey Team,
> 
> Lastnight I designed a board to extract 18 additional filter responses from
> my 2164 4P LPF, thus bringing the total number of filter responses from the
> module to 22 (4 LP, 4 HP, 6 BP, 2 N, 4 AP, and 2 more as yet unspecified).
> It will involve a 1U panel with 18 jacks on it sitting next to the 3U filter
> panel (hence my last query about PCB mounting), or it could just be a 4U
> panel.
> 
> I'd like to be able to look at the filter responses on my old Tektronix
> scope, but I'm not sure how.  I'm thinking a sawtooth sweep of expo FM on a
> sine-generating VCO into the filter at constant cutoff, and then perhaps
> taking the filter output through an envelope follower and then into the
> scope to see just the positive outline of the response.  However, if anyone
> has a nice method for doing this, I'd love to hear it.