TESORO GOLDEN SABRE

[Ultimate_Haze]

Remove 1-2 turns from it and test again. But first try to null coils to 4-5mV..
0.27mm bare wire...should'nt make any problem.

I made another RX 6,13mH this time/which is one turn less/.Nothing change.
I now that 0,27 shouldn't be a problem.
Thanks
Should I try less turns?
Those are shielded coils.So I cant change No. of turns.

[Qiaozhi]

Yes, this is what I meant.
It's Dennis' scope picture the one I posted...
Am I correct that the right nulling is achieved at position 0:11 of the first video that he published? (11 s after the start is the only way I can find to refer to that position... ), but that phase is anyway reversed in polarity...

You need to position the TX and RX coils so that you have a 20 degree phase-offset. In that position the ground balance pot can be adjusted to place the ground sample pulse over the negative-going zero-crossing of the RX signal. This will be somewhere near mid-position of the ground balance pot. You can then finely adjust the pot to reject the ferrite. During this test make sure the DISC pot is turned to minimum.

[ivconic]

I made another RX.This time 6,29mH.This don't make any difference.
I check again those TX caps they show 22 and 220n with Digital LC meter/DL6243/.I think its good because can measure right values on minelab coil.Maybe the frequency meter that I use is no good.Its DT9208.
This last wire that I used were 0,27 bare wire.

Remove 1-2 turns from it and test again. But first try to null coils to 4-5mV..
0.27mm bare wire...should'nt make any problem.

[Pompey]

I made another RX.This time 6,29mH.This don't make any difference.
I check again those TX caps they show 22 and 220n with Digital LC meter/DL6243/.I think its good because can measure right values on minelab coil.Maybe the frequency meter that I use is no good.Its DT9208.
This last wire that I used were 0,27 bare wire.

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This time your off resonance is 1,73 -not enough yet It must be around 1,85 khz

[Ultimate_Haze]

I made another RX.This time 6,29mH.This don't make any difference.
I check again those TX caps they show 22 and 220n with Digital LC meter/DL6243/.I think its good because can measure right values on minelab coil.Maybe the frequency meter that I use is no good.Its DT9208.
This last wire that I used were 0,27 bare wire.

[Stefano]

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.

Yes, this is what I meant.
It's Dennis' scope picture the one I posted...
Am I correct that the right nulling is achieved at position 0:11 of the first video that he published? (11 s after the start is the only way I can find to refer to that position... ), but that phase is anyway reversed in polarity...

[ivconic]

My coils are 5.9/6.7mH .I decreased 15nf to be able to make ferrite rejection in the middle of the GEB pot.For discrimination pot I use 20k instead of 100k. It reduces Tx signal from generator and also makes sinus correct -without this crack on the edge.Also I changed one of 100pf caps -those to LF353 -to 47pf.It reduces signal at pin 1 -sinusoide with some cracks.I hardly can detect 1euro -25-27 sm only with very fast moving the coin..

With 15nF your RX coil is +1.23kHz off resonance. Not good. You also need RX = 6.2mH and to return back 15nF there...
Regards!

[Pompey]

My coils are 5.9/6.7mH .I decreased 15nf to be able to make ferrite rejection in the middle of the GEB pot.For discrimination pot I use 20k instead of 100k. It reduces Tx signal from generator and also makes sinus correct -without this crack on the edge.Also I changed one of 100pf caps -those to LF353 -to 47pf.It reduces signal at pin 1 -sinusoide with some cracks.I hardly can detect 1euro -25-27 sm only with very fast moving the coin..

[ivconic]

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.

Could be due bad nulling or bad RX cap...or something bad arround LF353.

[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.

[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..

[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]

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[ivconic]

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[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