Hotrock

Great article Reg. The term I was using, TX antenna coil and RX antenna coil was applied to incorrectly as far as metal detectors are concerned. The article expained that very well. The correct term used should be transmit coil or receive coil, and leave the antenna part out of it, which you did state. In this case, they do act like transformers, and I was wrong.

Your right Steve. I would like to thank Reg and commend him for helping others in our hobby.

Ok, then let us agree to disagree because of our understanding of the science and physics behind it is different. Since you can not explain how a coil wound on the base or in the middle of a TV rabbit ear antenna works, we are wasting time discussing how a metal detector's antenna coil works. Another example is a center load COIL on a CB antenna. "The windings in a coil act much like a transformer, which can have different polarities on the secondary." TRUE "In the case of a metal detector coil, the tx winding is the primary and the reiceive winding(s) are the secondary." FALSE. Can't be a transformer unless the coils are coupled. Primary and secondary is meaningless unless they are coupled. If you are determine to argue that the TX coil and the RX coil forms a transformer, then what is the coupling coefficient value? To understand how antennas coils work, one needs to take an electro magnetic course that discusses antenna configuration application.

Reversing the signal phase of a receiver antenna output sign signal by reversing the Hi/Low antenna connections can not change the polarity of the induced wave or field on the antenna element. If the antenna element is the transmitting antenna coil then reversing the feed leads will momentarily reverse the radiated wave polarity. Certain kinds of receivers can detect this polarity interruption and use it as a timing marker. You are confusing reception post antenna signal polarity with induced wave antenna polarity. You are getting antenna wave or field polarity mixed up with antenna output signal polarity. There is a difference. I think we are talking semantics, which may be confusing when different terms are loosely used in a broad context. If physically flipping the receiver antennas or connections affect the detector's performance, then it is the post antenna signal processing configuration that is affected, not the antenna configuration. In other words, the same results could be achieved with a different post antenna signal processing circuit configuration, which means that it is not just an antenna gimmick.

Each receiver antenna output feeds into a SUM/DIFFERENCE power combiner. If the two receiver antenna output signals are in phase, then the two signals are summed together for a 3 db gain out of the power combiner SUM port. However---the ground noise is also summed. If the two antenna output signals are 180 deg out of phase, then the power combiner DIFFERERNCE output port will yield a 3 db signal gain, but--- the two receiver antenna output ground noise signals will be canceled leaving only a 3 db signal gain. In other words, the ground noise signal is absent at the power combiner DIFFoutput port. Flipping the receiver antenna coils or connection wires does nothing to change this. The polarity of the received signal wave or field determines the receiver instantaneous antenna polarity regardless of antenna configuration or orientation. Installing a 180 deg signal delay line between one antenna output and one power combiner input port will yield a 3 db signal gain with about 20 db ground noise suppression out of the power combiner DIFF port. This is what you want.

Question? How do you change the recieve wave polarity, when the transmitter sets the polarity?

The GPZ could someday have the capability of switching back and forth from the Time Domain (PI) type of target processing to the Frequency Domain (VLF) type of processing at the operator's command. This feature would require no hardware design changes. Or if the signal processing is designed to accommodate both types of signals, then the targets could be displayed as Frequency Domain (FD) detected and/or Time Domain (TD) detected, simultaneously. Indication of both types of detections to the operator could be displayed. Only targets that have certain characteristics may be detected in both modes. Both FD and TD modes. This could be viewed as an additional target discrimination feature.

Hi AussieMatt, see the thread further below labeled ZVT technology. http://www.detectorprospector.com/forum/topic/682-zero-voltage-transmission-zvt/ It might address some of the answers to your questions. It's not necessarily a pulse induction, but behaves as a pulse induction because of a timing marker being introduced. The difference in the two, is the way the signal processing technique is done with CW (continuous wave). The different tones of targets is a function of target pearmability. This is just my understanding of this kind of technology based on what I know, and what has been let out of the bag so far. I could have some things wrong though.

Great post Steve. I share the same sentiment.

I haven't read or been reading any patents.

In full wave rectification, all the negative or positive 1/2 cycle waves are clipped or missing. If the negative swings are clipped or missing, the rectifier output is a positive DC voltage. If the positive swings are clipped the output is a negative DC voltage. The picture you have in mind is valid except for the metal detector transmitter output, only one cycle is clipped or removed then everything returns to normal as it was before the single cycle was clipped. The one missing 1/2 cycle is the introduced timing marker used in signal processing time delays, which are functions of metal target materials.

In an instant of time, when the transmitter instantaneous output sine wave voltage that is driving the antenna element, crosses the zero voltage level on the way to the next expected maximum peak postive voltage level, is then reversed or switched at the ZERO VOLTAGE point, or crossover, so that it then returnes back to its previous maximum negative peak voltage level instead of the next expected postive peak voltage level. That instantaneous antenna polarity switching function introduces a timing marker just as the pulse cutoff function introduces a timing marker in a pulse induction system. The antenna polarity switching, which must occur at the transmitter instantaneous output zero voltage level, thus allows one to label the system as "ZERO VOLTAGE" detector. It's a new signal processing process. This allows a VLF continuous wave detector to behave exactly as a PI system.