A couple of scope shots showing voltage across bifilar coil,and voltage across pickup coil.
Second shot showing current through bifilar coil,and voltage across pickup coil.

At this frequency,the voltage across the pickup coil is in phase with voltage across bifilar coil,and not in phase with current through bifilar coil.


Brad

The below scope shot,is to try and  get the single wound coil to ring-in the same way i did the bifilar.
As you can see,it rings down very quickly.
Tried a frequency sweep,and this was the best result.


Easy to see the bifilar coil rings down a lot more.

Quote from: Magluvin on April 15, 2017, 08:13:52 PM
I picked the wire for this some time ago when a RS store was going down for the count. was 29 bux and got 60%off so it was a no brainer. The flatness of the copper should give more surface area proximity than round wire per turn, that was my inspiration for going flat, to increase the capacitance.  Like imagine say 1in wide copper tape or even wider. A nice increase in both capacitance and induction in a similar sized dia with a thin insulation layer between turns.

I feel good with the outcome of the capacitance and the inductance. I was also happy with the 85khz as it clearly shows a decent amount of inductance and capacitance to not only go lower than the mhz range, but i wasnt expecting below 100khz. How many ohms is the series total on your coil?

Mags

The two bifilar pancake coils measure 3.90 ohms and 661 uH and 2.19 nF,  and 3.90 ohms and 685 uH and 2.20 nF, including the connections. The matching monofilar coil I wound yesterday (bitch!) measures 3.92 ohms and 712 uH. It may have a couple more turns on it than the bifilars, from the looks of it.

Still haven't measured resonant frequency, have been busy with other things this evening.

Quote from: tinman on April 15, 2017, 08:57:21 PM
So,when we say!self resonant frequency!,do we simply keep raising the frequency until maximum voltage amplitude is reached across the coil?

If so,who can calculate what mine should be,using the values given in my last post?.


Brad

With 1.22 nF and 0.02 nanoH I get 1.0189 GHz. With 0.06 nH I get 588 MHz.

But I must say those inductance values are implausible, even if you mistakenly connected the coil as a hairpin bifilar instead of a Tesla series bifilar.

Here's an inductance calculator that will show you that even the meter's connecting leads will probably have more inductance than that. You are talking short PC board traces, for that low inductance.

http://www.consultrsr.net/resources/eis/induct5.htm

How are you measuring the inductance to be that low?

Your recent scopeshot of the ringing appears to show about 6.2 oscillations in 5 microseconds (2 divisions) which should be a frequency of about 1.24 MHz.

So taking the 1.22 nF capacitance and that frequency and working backwards for inductance, we should have about 13.5 microHenry. Even that seems low to me.  The bifilar coils and the monofilar coil I showed earlier each have inductance of around 700 microHenry. Are you sure we are seeing the coil ringing, and not your probe leads?

http://www.1728.org/resfreq.htm


Are those two traces at 40.5 kHz at the resonant frequency point? (oops sorry I had MHz instead of kHz)

Can you expand the trace of the single winding coil so we can read the frequency from the graticule? At first pass it looks to be a bit higher ( around 2 oscillations in one microsecond)than what you got with the ringing of the other coil ( around 6.2 oscillations in 5 microseconds).

OK,regarding my last post and scope shots of ringing.

Some twat forgot to include the 1 ohm CVR in the single wound coil ring test. 

Below is the amended single wound coil ringing scope shot ,alongside the bifilar coil.

Looks much better now.