I got one of these early 1970's Krohn Hite 3202 dual Hi/Low filters - online.
The switches were stuck, but some good DuPont silicone lube freed them up. Also, I cleaned the switch contacts and sparingly applied some DeOxit, plus I installed all new electrolytic caps.
This filter now works, but I want to have a go at Calibrating it.
I have a R&S RTB2004 modern scope, and a Tek 2246 scope, and Fluke 189 handheld RMS meter.
DC offset adjust is good, at less than 0.8 milli vdc.
But the other instructions have me confused.
STEP #1 ....looks like 600hz @1v is sent to the filter input and the scope input, and the output also to the scope, in X/Y mode..... and look for an "ellipse".
All I get is what I expected.... an "in phase" 45deg straight line, and that does not change with turns of the dial.
I'm also not sure what they mean by "20 divisions" ?
Also, with only 1.0 volt input, how does the VTVM read 20 dB ? Is the VTVM on a different scale setting ? Because with my DVM on dB mode, 1v is 0.1 dB....and.... 20dB is about 10vac.
Here is a meter scale from an older VTVM.......
(thumbnail)
The switches were stuck, but some good DuPont silicone lube freed them up. Also, I cleaned the switch contacts and sparingly applied some DeOxit, plus I installed all new electrolytic caps.
This filter now works, but I want to have a go at Calibrating it.
I have a R&S RTB2004 modern scope, and a Tek 2246 scope, and Fluke 189 handheld RMS meter.
DC offset adjust is good, at less than 0.8 milli vdc.
But the other instructions have me confused.
STEP #1 ....looks like 600hz @1v is sent to the filter input and the scope input, and the output also to the scope, in X/Y mode..... and look for an "ellipse".
All I get is what I expected.... an "in phase" 45deg straight line, and that does not change with turns of the dial.
I'm also not sure what they mean by "20 divisions" ?
Also, with only 1.0 volt input, how does the VTVM read 20 dB ? Is the VTVM on a different scale setting ? Because with my DVM on dB mode, 1v is 0.1 dB....and.... 20dB is about 10vac.
Here is a meter scale from an older VTVM.......
(thumbnail)
....and for some reason it's working now, I see an elipse, and can close it at 135deg angle.
User error ? prob.
Last night, I was using the included freq generator on the R&S scope. Both X and Y were aligned in phase......so of course I got those old expected results.
Today, I'm using an outside sig generator (a modular synth oscillator), and the X/Y signals are 180 deg out of phase going into the scope.....giving me an elipse near 135 deg. Dial on the filter closes the ellipse. It happens to be spot-on !!
🤓
I'm still not sure about the "20 dB" though, in the next steps.
(thumbnail)
User error ? prob.
Last night, I was using the included freq generator on the R&S scope. Both X and Y were aligned in phase......so of course I got those old expected results.
Today, I'm using an outside sig generator (a modular synth oscillator), and the X/Y signals are 180 deg out of phase going into the scope.....giving me an elipse near 135 deg. Dial on the filter closes the ellipse. It happens to be spot-on !!
🤓
I'm still not sure about the "20 dB" though, in the next steps.
(thumbnail)
Manual? If it is not making sense, maybe a step or footnote has been omitted?
Krhon-Hite 3202 filter manual
https://neuron.eng.wayne.edu › ece4340 › kh-3202
https://neuron.eng.wayne.edu/auth/ece4340/kh-3202.pdf
I think they want you to bring it to 1V in one setting, then set another setting and expect 0.707V (down 3dB, like 20dB to 17dB).
Krhon-Hite 3202 filter manual
https://neuron.eng.wayne.edu › ece4340 › kh-3202
https://neuron.eng.wayne.edu/auth/ece4340/kh-3202.pdf
That may be the specific ACVM (a 'Boonton') which K-H wanted you to use. It has 4(5?) ranges. Full-scale on each range is marked "20dB". Therefore 1/10th scale is "0dB". There is no absolute reference for the dB; depends on the range.
I think they want you to bring it to 1V in one setting, then set another setting and expect 0.707V (down 3dB, like 20dB to 17dB).
That's sort-of what I'm guessing too. The manual mentions the Ballantine 310 VTVM, pictured above.
But I'm thinking that "20 dB" means "full scale (of 1 volt)".
With the filter well within the passband (no filtering) 1v at the input should give 1v at it's output. (lowpass at 60kHz cutoff, (600hz @ 100x switch setting)
When within the filter's 'sphere of influence' (wink) there is some attenuation at the 6kHz cutoff (600hz @ 10x setting)....so, -3dB.
This is what I am understanding so far.
But I'm thinking that "20 dB" means "full scale (of 1 volt)".
With the filter well within the passband (no filtering) 1v at the input should give 1v at it's output. (lowpass at 60kHz cutoff, (600hz @ 100x switch setting)
When within the filter's 'sphere of influence' (wink) there is some attenuation at the 6kHz cutoff (600hz @ 10x setting)....so, -3dB.
This is what I am understanding so far.