Zero Voltage Transmission (ZVT)

[Hotrock]

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.

[Reg]

Hotrock,

 

"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."

 

OH!!! Really?????

 

How do you reverse the phase of a winding? 

 

You really should build one and try it before making such statements.

 

BTW, I have built dozens of DD coils and used the simple technique of flipping the windings when the polarity is wrong.  Worked every time.

 

Reg

[Hotrock]

  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.

[Reg]

Hotrock,

 

Please learn the difference between a coil of wire used as a transmit or a receive winding and an antenna.  The windings in a coil act much like a transformer, which can have different polarities on the secondary.  In the case of a metal detector coil, the tx winding is the primary and the receive winding(s) are the secondary. 

 

This idea is not the same as a set of bunny floppers you used to use on TV's. 

 

Changing the output polarity of any receive winding on a DD coil or the DOD design can be reversed by simply flipping the secondary winding.  It works no matter how hard you try to convince the unknowing it doesn't. 

 

Now, I have wasted enough time on this trivial issue.

 

Reg

[Hotrock]

  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.

[Steve Herschbach]

Come on guys, we are here:

A. To have fun

B. To educate others in language understandable to the layman

Hotrock, Reg Sniff makes his own metal detectors, he winds his own coils. He is well respected by many in the industry. I would hate to have him leave the forum.

[Hotrock]

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

[El Dorado]

I have a headache now

[Reg]

Eldorado,

 

A metal detector coil isn't an "antenna" even though many people refer to it as such.  Here is an interesting link to the basics of a detector coil in simple terms. 

 

http://www.geotech1.com/pages/metdet/info/coils.pdf

 

Here is an interesting bit of history. 

 

http://www.deeptech-bg.com/search_coils.pdf

 

As for the rest of the rest, well, Mrs. Brown has a perfect response she learned in elocution lessons and that is, "That's Nice".

 

Reg