DD coil balancing again

[Pep_T]

How about nulling circuits? I saw them in a couple of designs but never tried them.

[nejdet]

How about nulling circuits? I saw them in a couple of designs but never tried them.

Works well!

[remi007]

Hello. Is it possible to make a DD probe for Whites 6000 di pro sl? Years ago I tried to make one while maintaining the RX TX inductance of the BM950 probe. My problem was that in one of the channels the response to metal was the opposite, as a result the signal died down instead of getting stronger when the metal was brought closer to the probe. What was I doing wrong? Was it just badly tuned? How to tune such a probe so that it would have the same response as the BM950? At that time I spent too little time investigating the issue. He who asks, wanders less. Thanks for any answers?

[gurdal]

How about nulling circuits? I saw them in a couple of designs but never tried them.

Hello everyone,
What is JP1 in the circuit?
Can you write in detail how the circuit works?
Thank you very much.

Best regards
Gurdal

[Carl-NC]

Hello. Is it possible to make a DD probe for Whites 6000 di pro sl? Years ago I tried to make one while maintaining the RX TX inductance of the BM950 probe. My problem was that in one of the channels the response to metal was the opposite, as a result the signal died down instead of getting stronger when the metal was brought closer to the probe. What was I doing wrong? Was it just badly tuned? How to tune such a probe so that it would have the same response as the BM950? At that time I spent too little time investigating the issue. He who asks, wanders less. Thanks for any answers?

Short answer is 'yes'. I don't know what you mean by "one of the channels"... one of the modes? one of the signal channels? It's possible you had the RX coil connected backwards, just reverse the wires to correct.

[Carl-NC]

What is JP1 in the circuit?
Can you write in detail how the circuit works?

I assume JP1 is a jumper, either connect 2-1 or 2-3.
RV1 & RV2 alter the phase & amplitude of the signal that is injected into the RX coil to null out any physical imbalance.

[gurdal]

I assume JP1 is a jumper, either connect 2-1 or 2-3.
RV1 & RV2 alter the phase & amplitude of the signal that is injected into the RX coil to null out any physical imbalance.

Thank you very much

[Pep_T]

Exactly, the whole circuit is just a passive filter that allows to take a portion of the TX signal and add it to the RX signal. The two potentiometers are used to define the amplitude and the phase of the input signal portion, and it has to be added to either the inverting or non inverting input of the RX preamp, hence the jumper. The goal of the circuit is to DECREASE the RX amplitude simulating a better balance of the DD coils. Clearely we actually want to SUBTRACT some signal to the RX, but it is all a matter of the potentiometer regulations.
I tried it in my circuit, it kinda worked, but I am sure that the values needs a little tweaking.
Eventually I did not even used it.

[gurdal]

Exactly, the whole circuit is just a passive filter that allows to take a portion of the TX signal and add it to the RX signal. The two potentiometers are used to define the amplitude and the phase of the input signal portion, and it has to be added to either the inverting or non inverting input of the RX preamp, hence the jumper. The goal of the circuit is to DECREASE the RX amplitude simulating a better balance of the DD coils. Clearely we actually want to SUBTRACT some signal to the RX, but it is all a matter of the potentiometer regulations.
I tried it in my circuit, it kinda worked, but I am sure that the values needs a little tweaking.
Eventually I did not even used it.

Thank you very much