Please tell us how your wonderful deep penetrating Surf PI 1.2 coil is made.

[kenny444]

Hello and thanks for reading and replying to this thread.

Would you please spare a few moments tell us out here all about your super efficient Surf PI 1.2 coil?

Diameter,
Wire type,
Wire size,
Resistance
Measured inductance
Coil housing,
With or without screening,
Spacer type and width, (between coil and screen)
Connecting cable (screened or not and earthed where)?

Please add anything else that may guide us, that are out here in the land of mediocre coils.

Thank you very much.

May there always be gold at the end of your rainbow.


My coils well OK:
8,9 & 10 inches, all made with .5mm enamelled copper wire, 16 to 25 turns, all fail when screened, all produce some form of mad morse code (which does not go away) and is induced from who knows where, (I live in Milton Keynes and most of the houses were cabled up for radio and TV when built, so that may be the cause) they air test at about 4 inches and then go deaf, I am not going outside with them as I am too ill and suffer from being cold and I cough for England, I cannot test the uH as the chinese man who was sending me one has so far failed to do so. R is low in all cases. Offsets are at about 0.002 of a volt but the meter has limitations. Yes I adjusted the Delay, but as I am swamped with interference its hard. Yes the battery voltage is OK 11.5ish at the last inspection, current draw is about 40mA.

Is my board set up OK, to be honest the 3 boards I made this last month all do the same thing, have I got some faulty IC's, that is unlikely as I have the 3 boards working the same and I also have 2 full sets of chips as well that have been replaced individually to fault find by substitution, does anything change, sadly not.

So if the chaps with the big air tests would kindly share there information, that would by very very nice of you.

Ever so grateful.

Kenny

[Silver Dollar]

Well you probably built yourself an incredibly slow coil. I've built a fair number and some work
quite well (though I do not have a working PI detector yet). I've found the inter-winding
capacitance will slow your coil way down. If you use magnet wire you need to at least wind
it basket style to keep the windings away from each other. Like this;

http://www.geotech1.com/forums/attac...1&d=1414104068

Better would be teflon coated stranded wire or basket wound litz. If you have a scope you
can see how slow it is by monitoring the First op amp output.

[kenny444]

Firstly thank you for the prompt reply and your input.

I have tried to reply in a polite and courteous manner, but I now have even more questions regarding the building of a good coil for the Surf PI 1.2 MD, because you have raised points I had previously not considered or was not aware of. So I have broken down your points into sections with a hope that you can help further by addressing these points.

I also wish to say that I respect that you may think that that lack of knowledge is detrimental, but when the gaps are filled in then you will have helped many future MD builders and they and I will be very grateful to you.

Our first challenge is that when we buy a Surf PI 1.2 PCB, that is what we get, no manual or information, so we all follow the route of tracing the WWW for hints, tips and suggestions, That is why I asked the questions in this topic.

The coil may be slow (but how can I/we tell, how fast should the coil respond for this design)? (Where can we the builders of the Surf PI 1.2 PCBs find the information of how to build a suitable coil)? and (What criteria are important)

The inter winding capacitance may slow the coil down (but how is this avoided, surpassed and cured)?

What is Magnet wire? and from that what is Non-magnet wire?

If a scope is used on the output of the first op amp, I/we will see a waveform, (but as I/we do not know what the wave form is supposed to look like or at what speed the waveform is supposed to be moving, how can I/we tell whether it is right or wrong)?

Are there any screen shots from oscilloscopes of the various waveforms and scope settings, relating to some/any testing points? and what timebase, etc.? Where if any, can we find reference scope photographs?

I do hope that this reads to you like it reads to me, as I do not want to cause any offence or raise any barriers. Please guide us and the world will be happier place because of your time and effort.

Regards and thank you again.

[Silver Dollar]

Well "enameled copper wire" is magnet wire. The wire with some kind of plastic coating is the other kind.
The plastic coating spaces the center conductor away from adjacent wires reducing capacitance. The same
thing happens with the basket coils the air gap reduces capacitance. Capacitance slows down the falling
edge of the transmit pulse. We need to wait for the transmit pulse to be done before sampling. Small gold
decays rapidly. So a coil that has too much capacitance will miss small gold as you cannot look for it until
the transmit is done decaying.

A PI detector will work with most any coil but a slow coil will filter out some targets. If you set it to see
big/deep targets it will also not see small/shallow targets. The first limit is how fast it is (IE how soon
can you sample and see a target?). The next limit is how much power is being sent out?

Once you have a fast coil with a lot of power you then adjust it to see the size/type of material/depth
object you are looking for.

I have some pictures but had to rebuild my computer last night so will dig them off my backup drive tonight...

[kenny444]

Thank you again, so a coated cable (Teflon?) has less capacitance because of the insulation spacing, sounds good. Is there an optimum insulated wire size .5mm?(24Awg) .6mm?(22Awg) - 1mm(18Awg) for resistance/inductance/capacitance? then single core? multi-core? Is there an article about basket coils somewhere?.

Very grateful, hope you get over your computer troubles.

Respect to you.

[Silver Dollar]

The key to wire size is to not allow the coil to see itself. A large solid wire (0.9mm) can be seen by the coil.
Multistranded is better especially if it is tinned as the silver conducts too well. Low resistance can allow more
current but sometimes a resistor is installed inline to "flat top" the current and speed up the coil.

There are a few different basket coil articles but again I'll have a look for them tonight...

[kenny444]

Thank you, I really am appreciating your information. What has crossed my mind is this The Detech Ultimate 13" coil is a nominal 14 mm diameter, which raise the question, what is inside there? A tuned circuit? Anyway I am thoroughly enjoying my education, very grateful.

[WM6]

The Detech Ultimate 13" is for VLF/IB systems not for here discussed PI.

[kt315]

nothing of info on all Detech coils. you have to read about whites Double Field coil, the spiral coil of Chemelek, the basket coil, thats all you may find here. those info
is much.

[WM6]

nothing of info on all Detech coils..

It is from inside applied technology all about clone coils, but very well made clone.

Not to say Detech detectors, like EDS Plus II, it perform best (regarding depth in first line) in my tests.

Detech is really good brand.

[kenny444]

Sorry for the confusion, I asked the question as I have ordered a 14" coil housing for the PI MD, and I assume that it is similar to the Detech 13", in size and therefore has a limited coil space. Which in turn limits the coil type and number of windings. How small then can a basket coil be made is another thought, could one be wound on something like thin rubber tube or even heat shrink? Hope this clarifies the situation.
here is what I have coming.

[kt315]

try basket coil http://metdet.ru/Sensor_K1.htm but add inside second winding so there will be a hybrid - Double Field Backet coil

[WM6]

For such big and small windings spaced coil housing, you need to use Cu enameled wire >0.5mm in diameter. Nothing like Teflon or PU isolated cable will suit in such housing (it is primarily intended for VLF/IB coils). For lower inner parasitic capacitance you can wind it in some sort of zig-zag manner.

[kt315]

yes, he needs maybe to use the litz wire.

[mschmahl]

Hi kenny444.
For Surf-PI you can make a easy normal round coil.
I have attached a description for a good coilfor the mirage (a hammerhead-clone from Sven). For the Surf you can make it similar with around 220 uH (leave a few windings away). Than it should work.