TESORO GOLDEN SABRE

[ivconic]

"...All have too high residual voltages.Around 1mV..."


So if you have 1mV residual voltage....hmmm....than your coil is "undernulled" or maybe you reached situaton where your multimeter cannot measure accurately. Generally, conventional multimeters are not best tools for measuring residual voltage. Good as something to start with, but not accurate. Scope is only solution.
Chasing less possible voltage on your multimeter you "undernulled" your coils and choked it, that's why it is not so good.

[ivconic]

For a series resonant circuit the reactances (L and C) will create a very low impedance, whereas for a parallel circuit the reactances result in a very high impedance.

The TGSL uses an opamp for the RX pre-amp with a high impedance input and is configured as a voltage amplifier. Therefore I would not expect a series resonant circuit to function correctly in this configuration.

Give it a try and let us know the result.

I already tested yesterday on my diy Eldorado (i don't have TGSL right now).
An you are right, not good.
It will need more changes to make it to work descent. I am not planing to do that, i just experimented a bit to see the differences in practice...

[Ultimate_Haze]

Hello,
So it might be multimeter that is wrong.I will try with oscilloscope.What you recommend?Directly from RX or LF353 pin7?
It still might be bad component no matter that I remove most and test those.
Tonight I will remove all.Just to make shore.

[ivconic]

Hello,
So it might be multimeter that is wrong.I will try with oscilloscope.What you recommend?Directly from RX or LF353 pin7?
It still might be bad component no matter that I remove most and test those.
Tonight I will remove all.Just to make shore.

No it is not wrong. Simply it is not designed to measure such values. Although...i also have conventional multimeter (brand new, bought it 3-4 months ago) and i can measure 4mV...7mV...etc.
Well...there are 2 methods suggested. Both are ok. My method is directly from RX coil (no caps, no resistors..).
...
But seems you missed the point. Check how much is your RX coil off resonance from TX.

Connect TX coil to TGSL TX out and measure frequency on 2N2907 collector.
Than connect RX coil to TX out and measure frequency on 2N2907 collector.
Than let me know here...

[gurdal]

Hi ivonic, if damage is plastic box

[ivconic]

?

[Pompey]

" ...Is there a possibility that when even the nulling seems fine , the sensitivity is poor ?..."

"Nulling seems fine" but you must understand that coils nulled well on one frequency are not nulled well on another (different) frequency. Residual voltage rised if frequency changed.

I think Qiaozhi already gave here good hint. Keep RX coil resonance within +1.8 - +2kHz than TX coil.
And use pp caps.

BTW thank You very much on your effort making those clips!
Best Regards!

************************************************** *
I think if you are able to adjust geb pot -rejecting ferrite somewhere in the middle off resonanse is OK -about 1,8-2,2khz. By adding,removing capacities to 15nf and playing with geb pot you can find the exact place where the ferrite is rejected not at any of ends of the POT,but somewhere in the middle.I think this happens when you achieve correct off resonance.But at the ferrite rejection has influence and this 220nf capacitor from pin 7 of LF353.By changing it you also may achieve ferrite to be rejected at correct point of geb pot.So what the experts will say?

[Ultimate_Haze]

DD27/TX 5,89mH;20,7ohms freq.13,9
RX 6,38mH;21,5ohms freq.13,4

[Pompey]

DD27/TX 5,89mH;20,7ohms freq.13,9
RX 6,38mH;21,5ohms freq.13,4

Hi ,Ultimate Haze.My last Tx coil is 5,9mH,and workin frequency is 14,53khz.I use 0,27mm. It seems your LC meter doesn`t measure exact inductances.I use my LC-meter in 200mH range to measure.When I put it on 20mH it gives mi incorrect inductance -raises up to 2mH.I measure frequency with 3 different meters - one multicet,LC-meter(multicet) and with PC-osciloscope -sound card.LC-meter gives 350 hz less frequency than the others.The pc and the other multicet show the same.

[Stefano]

Maybe I have not clear what is the requested phase difference...
I thought that the rx signal shold have been on the right of tx to have a positive difference.
Dennis' , as I see form his picture, looks negative to me.
So my questions to the gurus are: is this phase relation correct for a coil properly nulled? Should it look the same both at input and at the output of the preamplifier ? (I mean phase, not amplitude...)
Thank you
Stefano

[ivconic]

...

[ivconic]

...

[ivconic]

Hi ,Ultimate Haze.My last Tx coil is 5,9mH,and workin frequency is 14,53khz.I use 0,27mm. It seems your LC meter doesn`t measure exact inductances.I use my LC-meter in 200mH range to measure.When I put it on 20mH it gives mi incorrect inductance -raises up to 2mH.I measure frequency with 3 different meters - one multicet,LC-meter(multicet) and with PC-osciloscope -sound card.LC-meter gives 350 hz less frequency than the others.The pc and the other multicet show the same.

Wait a minute! Pompey is right! Something is not right there?
U.Haze are you sure your TX caps are 0.22 and 0.022 ? Looks like you have bad or wrong caps there!?

[ivconic]

Actually your RX coil is +1.61kHz off resonance - to low! You need 6.2mH for RX coil in this particular case where TX=5.89, TX caps are 0.22nF + 0.022nF and RX cap is 15nF!
But first you must check those TX and RX caps and if those are good than your inductance meter is not accurate....or frequencmeter is not accurate..

[Qiaozhi]

Maybe I have not clear what is the requested phase difference...
I thought that the rx signal shold have been on the right of tx to have a positive difference.
Dennis' , as I see form his picture, looks negative to me.
So my questions to the gurus are: is this phase relation correct for a coil properly nulled? Should it look the same both at input and at the output of the preamplifier ? (I mean phase, not amplitude...)
Thank you
Stefano

You should measure the RX initial phase-offset at the output of the pre-amp, as that's the signal which is sampled by the synchronous demodulators. In your photo of the scope the phase-offset is incorrect. For a DD coil it should be about +20 degrees, but you're showing about -50 degrees.