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Thanks Thomas Breuer!

A

Anonymous

Guest
Hi Thomas,
Built your receiver circuit, it works great. Had to take a look at these signals at transmitter turn on. The waveforms look just like Eric and others posted. Thanks so much for this information, and circuit information.
Thomas is right, anyone interested in PI should build this and take a look at the signals in the metal. Unreal!
There is just too much information at turn on to ignore. I'm sold and signals are strong. However, requires the use of some form of induction balance arrangement to use them. Then thats going to require some form of auto nulling to get really good performance. (That's one problem to work on how to do this on PI)
Reread your patent, Dave J., it had been years. I've have best luck feeding back with a single loop coil on the vlfs I've played with this on. Interesting to see your feedback coil.
Now comes the fun part, Anyone know of a way to cancel the on time transmiter signal from the front end amplifier on a PI? Some how feed the xmit signal into the summing junction on the first high gain amp. (not this simple is it?) And be able to see these signals during on time. And still use a monoloop if you wanted to?
DJ, don't forget the other patents unders More Light Reading post down below.
JC
 
Hi JC,
I have just updated the CC circuit. The new GIF will show up in my old message of Jan 6, 2002. Also, the PDF is new: www.tb-electronic.de/pi_tech/pulse_cc_circuit.pdf
There are just two parts added: A BS108 MOSFET in parallel to the internal N-CH MOSFET of the CA3130 plus a resistor of 1k from the output of the CA3130 to GND. The previously mentioned ringing at the point where the current ramp turns over into CC is almost eliminated, and the overshooting is also reduced. Coils are a bit stubborn, they don't like their current to be controlled this way ...
Concerning cancelling the TX signal electronically: Yes, it is possible, but the compensation of balanced coils is much better and stable. AFAIR I made some tests with a transformer measuring the TX current as well as directly subtracting a portion of the TX signal from the RX signal. I don't remember the details at the moment, but the results were not very promising (large TX voltage vs. small RX signal, drifting of the TX current due to temperature changes etc.). It might work OK in a test circuit where sensitivity doesn't count, but not in a real metal detector.
Thomas
 
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