DD coil for Surf PI

[6666]

Thanks Reg.

[tigershark_0]

Hi, thanks for rapid answer, I bought from UK,
I might first try single coil, to verify that the PCB works.

Still one or two month before snow will melt... so I have time o test a lot :-)

BR
Johansa

[6666]

For those that dont have a CRO, here is a Simple experiment of balancing separate transmit and receive OO PI coils, tx side is from surf pi up to the diodes, rx is just a coil with a pot to stop ringing , the bottom trace is the receive signal, coils are just random coils from junk box about 250uH . As the coupling changes from over to balance to under you will see the Rx signal phase change. I think the words over coupled and under coupled is correct. The Rx phase can be changed by flipping the coil over or swapping the leads.
The video is not the best, it was made on a very hot day 42'C, and it was done with 1 take.

http://youtu.be/Olmm9PecgE0

[greylourie]

For those that dont have a CRO, here is a Simple experiment of balancing separate transmit and receive OO PI coils, tx side is from surf pi up to the diodes, rx is just a coil with a pot to stop ringing , the bottom trace is the receive signal, coils are just random coils from junk box about 250uH . As the coupling changes from over to balance to under you will see the Rx signal phase change. I think the words over coupled and under coupled is correct. The Rx phase can be changed by flipping the coil over or swapping the leads.
The video is not the best, it was made on a very hot day 42'C, and it was done with 1 take.

http://youtu.be/Olmm9PecgE0

Thanks for the video. Very nice instruction/example.

[drbean]

Hi I have tried the coil tech 11 inch mono and 9 inch
Very sesative no good in minrilised rock in aussi .
made one from enamiled wire that wasnt to shabby but still
would advise dd not finding to much difference in sesitivity.
Still would be better to have ground balance .
Any idea Reg others have speculated i understand that it will take
a third sample .Oh I also tried 14 inch dd and it was quoted but seemed
to overload the unit on the amp not sure why.nice job on nulling dd reg.

[geoscash1]

Hey guys, new here and am planning on doing the surf pi project myself here soon.

Question for the experienced guys, when talking about using the mono coil and/or versus the DD, you mention removing one end of the TX resistor or R7.

Is there any reason a DPDT switch couldn't be added to the resistor or board so you could switch coils easily from one to the other mono to DD if you wanted both?

just curious, not a guru in electronics but know some basics. Thanks in advance.

[kt315]

geoscash1 the book INSIDE THE METAL DETECTOR is nice for first reading, for not a guru, for nub, for beginner, for dummy.

[geoscash1]

lol.... Thanks kt315... I'll have to assume from your reply my question was probably Purdy dumb.. lol

[Silver Dollar]

There is several hundred volts there when the TX fires, that might arc inside the switch and cause some problems.
Better to set it up the way you like and leave it that way...

[drbean]

Well my machine runs both off the mod mono and did and have set it up as reg suggested
Screwy like a rabbit but both coils sensitive will check it out next couple of days but dd is
Quieter mate.you could put a two way toggle switch in final housing like ml 3000 do.
We arnt all electronic geniuss here ,but with help from others is how we learn