Which is best Damping?

[Silver Dollar]

I finally got my Hammer Head partially working and realized I do not know
what correct damping looks like. With a high value resistance the signal
obviously rings but when you lower it I do not know when to call it good.

Here's a few waveforms;














And the one I chose as best (at 330 ohms);


Does that look good?

[green]

#4 or #5 flatten out sooner than the 330 ohm trace. Look like amplifier in traces. I was thinking amplifier out is a better place to monitor. Maybe I'm wrong.

[Silver Dollar]

I just realised I had a large metal target nearby. I had moved my scooter inside over the weekend
and not moved my testing area.

They are amp in traces, I was originally looking for the fly back and kept using the bottom of the
diode on the preamp input. I took my 2 stage off so currently only have a gain of 33. I'll move the
scooter and put the 2 stage back and see how it goes.

On some coils the whole response is quicker. I suppose this means they are faster coils but I do not
understand how we can see a target when the smallest delay is say 12 us and the response appears
to end at 4 us from the TX?

[Chet]

Hi Silver Dollar, attached for reference is a shot of the second stage output (TP3) of the Minipulse Plus Rev-C. The flat areas top and bottom are from op-amp saturation which needs some work/modification to reduce.

[green]

Hi Silver Dollar, attached for reference is a shot of the second stage output (TP3) of the Minipulse Plus Rev-C. The flat areas top and bottom are from op-amp saturation which needs some work/modification to reduce.

Hi Chet. Am I reading the scope trace correctly? It takes about 30 usec for the amplifier to come out of saturation after coil turn off?

[Chet]

Hi green, you are correct. The shot was taken with a home brew 8" coil. Attached is an improved example with a 6x9" Coiltek coil. It still has too much saturation time. The current plan is to increase the +/- voltage rails on the opamps to 9 or 12 volts. Install different opamps and reduce the gain if necessary.

[golfnut]

loving that scope

[Silver Dollar]

So I reran the tests with much better results.
My fastest coils were the Basket coil, The Blue AWG 30 wire wrap coil and the Octagon with centronix printer cable
All damped with 800 ohms;






The Litz Big Foot coil damped at 500 ohms;


The AWG 24 CT coil was a bit slow at 350 ohms;


My DD coil would not stop ringing. I used 200 to 1500 ohms on it and tried 1500 ohms on the other D but still ringed;

[Chet]

Hi Silver Dollar, Great job, good measurements. The Octagon coil recovery trace slope looks like it is detecting something.

Maybe a lower resistance (200-500 ohms) on the second D coil will stop the ringing.

[Silver Dollar]

Ya I thought of using a lower damping resistor for the RX on the DD I'll try that tonight.

Th octagon seems fast but looks different. The cable is 34 wires which I only used 17 so the
unused wires are floating in there, also I didn't ground the shield so I'll have to try that and
see how it looks.