moog HPF (inductor) ladder works ?

[Harry Bissell]

Harry Bissell writes: Before anyone can call me "full of shit", I tried Terry
Michaels' inductor ladder seems to work. I used EWB to run a sim on the all
transistor mini moog model "D" filter which was working well. Ladder current
maxes out at about 3ma, and the caps were .02uF. I replaced these with 10mH
inductors. Scope indicated HPF response to square wave (1kHz)input, and the Q
works the same as for LPF. I didn't check bode plots, or optimum inductor
value. 1mH was too small. Have to try adding the DC series resistance, it
might queer the Q badly (could be 5 -50 ohms series, and distributed
capacitance could be 50pf. The model also doesn't account for possible
saturation and non-linear core effects. And count on this, you woun't just use
an "air core" , probably a toroid ferrite. Try Tamura (microtran) I'm looking
at QG series???  Also the filter might peak at some ungodly frequency due to
stray "C" in the L-C. Might divert aircraft from their normal flight path ???
The simulation would go into self-oscillate mode. If anyone has a Ladder
breadboard, give this a try. I'll play more at work tomorrow... Who'd notice
an engineer running a spice simulation... looks just like a REAL job.  ;-)  
Harry

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