PI coil

[chemelec]

Hello Friends.
Thanks for the replay, very useful !
Some questions:
Thinkerer : In the past I have seen some ‘hollow’ coax. Do you think this is better than the one I used?
‘BBSailor: For measuring the self resonance from the coil; I connect a function generator at the cable to the coil and searchs, looking on the scope, for the highest amplitude? If so I can tray this next week. Or is there a better way ?
Best regards.
Ap

Here is my method for determining Free Air Resonance and Interwire Capacitance.

http://www3.telus.net/chemelec/Proje.../Reactance.htm

When Testing the coil as Shown "Connected to the Scope", The Coil MUST Be SUSPENDED in FREE AIR away from any objects and held with a Non-Conductive item.
(I use a long piece of plastic to hold the coil.)

[bklein]

I'm wondering how this coil compares to one with same outer diameter but wound as a single layer side by side (traditional) coil.... Why would your spiral be better?
I've never seen anyone here make one as I suggest.

[chemelec]

I'm wondering how this coil compares to one with same outer diameter but wound as a single layer side by side (traditional) coil.... Why would your spiral be better?
I've never seen anyone here make one as I suggest.

Yes, I remember one Other person made a coil like yours.

Your coil will have a Greatly Reduced Interwire Capacitance and MY GUESS, Probably a Free Air Resonance Up in the 4 to 6 MhZ Range.

Typically My coils are around 2 Mhz Free Air Resonance.

However, considering your Wire Gauge, it is probably also Fairly High in DC Resistance and Quite Low in Inductance.

Have you Measured either of these values?
Did you use my Setup to determine the Free Air Resonance and Interwire Capacitance?

[wallker]

Hello Friends,
Just for fun I made a coil from a old coax cable ( ca. 15 meter), striped it from the shielding and outside PVC, so only used the inside wire with its tick isolation. Look at the photo’s, not the most beautiful coil…, I made it with some hot glue and a old 24 cm coil form .
For testing I connected it on a Surfmaster-PI… the results for small gold are very good ! The small very thin gold medal can be detected ! ….. Other tested coils ignored it !
So if you have some old coax…

Hi ApBerg, could you tell me more about sensitivity on 1 euro coin and on soda can with this coil ?
Regards Marko.

[ApBerg]

Hi ApBerg, could you tell me more about sensitivity on 1 euro coin and on soda can with this coil ?
Regards Marko.

Hello Marko,

Just made some indoors test with that coil, 1euro at 27 cm, gold ring 28 cm , cola can 0,33l at 70 cm.
The small gold coin , very very thin at 7 cm, other Pi coils do not detect that coin !

Not very good… to my surprise… but now the coil is screened( grafit) and build in..

The first test without the screening were better I think to remember.

Only used this coil + Surf one time at the beach…found many iron objects.. windscreen ground pins…..lots of them and some very deep …some coins…….. no gold…

Best regards

Ap

[wallker]

Thanks for your reply Ap, I got similar detection with my barracuda, 1 euro 30cm, soda can 80cm and with razor blade something about 5cm.
All of those with this coil:

[UFO]

Looks good, I would like to try.

Can I ask how many turns is that, what is the uH and what is the outside diameter of the insulation?

[chemelec]

Thanks for your reply Ap, I got similar detection with my barracuda, 1 euro 30cm, soda can 80cm and with razor blade something about 5cm.
All of those with this coil:

I'll bet that is a HEAVY Coil.

[UFO]

I'll bet that is a HEAVY Coil.

Would be OK for a water coil?

[wallker]

@UFO I used stranded wire 0.5mm with some 54 turns, inductance is somewhere about 430 uH, don't remember about insulation thickness, but you can easily calculate it with this calculator : http://www.deepfriedneon.com/tesla_f_calcspiral.html
I think it would be ok to use it in water.
@chemelec It's heavy indeed, and because of that i used rod with the battery as a counterweight, described here : http://www.geotech1.com/forums/showt...&highlight=rod
Picture of wire :

Regards Marko.