Some "tiny" questions...

[Anonymous]

Hello to all.
Does anybody build a german P.I. called Tiny (www.pulsdetektor.de) ? I am very interested in hearing how this detector works on differents grounds (medium mineralised ground, beach...)
Concentric coils : is there a better method to wind a coil (for PI) to optimised the sensivity on small targets ?
Thanks.
Nico

 

[Anonymous]

Nico
There is not any simple answer to the question about coils. Part of the answer is given by the formula below for the signal strength of a small target along the axis of a concentric coil. By concentric I mean that both the transmit and receive coils are on the same axis and both lie in the same plane, and in this formula both coils are circular. In the formula, D is the distance from the target to the plane of the coil. Rt is the radius of the transmit coil. Rr is the radius of the receive coil.
The red curve in the graph shows how the signal strength varies with distance from the coil when the receive radius is equal to the transmit radius. This is what you get for a mono coil.
The blue curve is for a concentric coil that has a receive radius equal to one half the transmit radius and the transmit radius is the same as the red coil. Both the receive and transmit coils have the same inductance.
Notice that at close distances the blue coil gives a stronger signal than the red coil. So for small targets that can only be detected close to the coil a smaller receive winding may give a stronger signal. But the blue signal falls off faster with distance, so beyond a certain distance the blue coil will give a weaker signal than the mono coil.
The units for the horizontal axis of the graph are the radius of the transmit coil. So a distance of 2 Rt is a distance of twice the transmit radius.
You only get a simple result like this for concentric or co-axial coils. There is no simple way to get the result for a DD coil. Also the result is only simple for targets on the coil axis, so it is not simple to calculate the strength of the ground signal. This graph does not give any indication of the benefits of a concentric design with respect to reducing the ground signal.
Robert

 

[Anonymous]

Oooupsss... thank you very much Robert for your answer but i was wrong... i had bad explained what i want, sorry... and i was false... that was not a concentric coil...
i try again... i wanted to say...
"is there a better method to wind cable (wires) in the coil (mono coil as tiny's coil) to have the best perfomances on small targets ?"
... for exemple, i read somewhere (don't remember where) that parallel windings but only one cable height increase sensibility on small targets. Anybody can tell me something about ?
Thanks.
Nico

 

[Anonymous]

Nico,
This is a method for decreasing a capacitance of the coil. If you wind a number of turns in one layer only, and with an interval between the turns, you will get a nice small self capacitance coil. That will allow to use smaller delay time. Unfortunaly, the capacitance of the coax cable remains and the improvement is not so big.
Tony

 

[Anonymous]

OK thank you Tony.

 

[Anonymous]

So,
nobody built the Tiny PI from www.pulsdetektor.de ?
(The Tiny's project is under "Projekte" (projects), "Detektoren" (detectors) and then look for "Tiny")