Detector is beeping when nearing coil to the ground

[emir506]

Dear Friends,

I build a HH1,
and the 10 inch coil shielded with shield wire, I have took from a TV coax cable. I think it's called Scotch24.
However, when I near the coil to the ground, it starts to beep, although the coil is shielded.

1) Here is a picture of the coil. Does the coil seems OK.
The Shield is going around the coil, and I left 1cm gap between the ends.
Any tips for improvement. ?

2) As I could read, the problem of beeping when nearing the coil to the ground, has to do with Ground Balance. Right ?
Is there anything I can do , do prevent HH from this strange behavior.

Any advice is helpful for me.
Em

[taliesin]

Dear Friends,

I build a HH1,
and the 10 inch coil shielded with shield wire, I have took from a TV coax cable. I think it's called Scotch24.
However, when I near the coil to the ground, it starts to beep, although the coil is shielded.

1) Here is a picture of the coil. Does the coil seems OK.
The Shield is going around the coil, and I left 1cm gap between the ends.
Any tips for improvement. ?

2) As I could read, the problem of beeping when nearing the coil to the ground, has to do with Ground Balance. Right ?
Is there anything I can do , do prevent HH from this strange behavior.

Any advice is helpful for me.
Em

apart from anything else.the connections look a bit untidy if you dont mind me saying.try to keep leads parrallel.this will improve the "q" of the coil.have a look at your solder joints with a loupe or magnifying glass.
i have no experience with this detector .
good luck

[porkluvr]

Is there anything I can do , do prevent HH from this strange behavior.

Any advice is helpful for me.
Em

You might try adjusting for a longer primary delay time.

This may be unrelated to your beeping, but it looks like you have used magnet wire. Unless you know that your wire has extra insulation, or unless you don't have some PVC or Teflon insulated hookup wire to use, I think magnet wire is not a good choice for a PI coil.

Magnet wire will give you higher inter-winding capacitance and a greater chance of insulation breakdown, and those are things to avoid.

edit: It occurs to me that if your coil does indeed have higher than usual capacitance, then you might want to try a smaller value of damping resistor and see if that helps. That is not a particularly good fix, because it indicates that you definitely want to make a better coil.

[Alexismex]

hello Emir
Like say porkluvr say it is true for the magnet wire (it is not agood choice for pi coil)
It is very better and good to use telefone wire from 1 pair to 5 pair
you can make your pi coil with the pvc ... it has good isolation and work very well i have make my small coil 11 inch with it with low inductance also
http://www.berliaelectricals.com/pag...one_wires.html

[Wiltran]

@ Alexismex I have made magnet wire PI coils. but how would you wind a stranded pair coil? Any example with pictures?

[Qiaozhi]

As I could read, the problem of beeping when nearing the coil to the ground, has to do with Ground Balance. Right ?
Is there anything I can do , do prevent HH from this strange behavior.

Any advice is helpful for me.
Em

You can easily check if your problem is related to ground effect by waving a ferrite slug in front of the coil. You should even be able to ignore quite large chunks of ferrite such as half a pot core. Note, some ferrite rods will always elicit a response if moved extremely close to the winding itself. The bottom line is - if the ferrite is ignored, then the detector is not reacting to the ground.

However, if your soil is heavily mineralized, there will of course be a reaction.

[emir506]

Thank you guys, you helped me a lot.
I had also the idea, the coil could be the main problem, but I did like it was decribed in the HH article (there was said to use AWG26 wire).

I will try to make another coil and come with results.

[Alexismex]

Hello Wiltran,
today i make some photos of the constructiion of coil (a 16 inch diameter),see and you will understand the technique , i have made many coils like that , work very well , you mixing telephone cable AWG 24 to some AWG 22 o 20 to obtain your needing resistance (ej.2R) and you turns depends of the inductance you need ( ej: 450-500uH for me)

[Geo]

Hi Alexismex.
I don't see Shielding. Do you use it??

Regarsd

[Wiltran]

coil

@ Alexismex. I cannot understand the reasoning behind connecting the different types of wire. is there another article I can read to provide a better explanation? thanks.

[emir506]

Hello Wiltran,
today i make some photos of the constructiion of coil (a 16 inch diameter),see and you will understand the technique , i have made many coils like that , work very well , you mixing telephone cable AWG 24 to some AWG 22 o 20 to obtain your needing resistance (ej.2R) and you turns depends of the inductance you need ( ej: 450-500uH for me)

Can you tell me, what's the name of the black cable and the connector you used on this picture.
And how do I connect it on the Circuit board. ?

[Alexismex]

Hello Wiltran ,
it is easy..... if you want a coil with a inductance of 400uH and it give you 20 turns (for exemple) and you want a resistance of 2 R if you have 20 turns of awg # 24 it will give you a resistance of 3 R you need to adjust this with for exemple put 15 turns of #24 and 5 turns of #20 and you will sum 2 R at the final ,ok
With this method you can adjust exactly the resistance of your coil with cable with the inductance desired....
With pulse detector it is not so important with a variation of 10% but with minelab coil it is very important if you did not want to fried your pi
Alexis.

[Alexismex]

Hello geo ,
in this kind of coil i never shielding because you do not have many advantage if you worK with delay up to 25 ...40 uS (relics) and this coil work very well in hightly mineralised soil like in Mex
For gold research with fast pulse DD you need some shield and i shield with carbon sheet

[Alexismex]

Hello Emir ,the cable is RG 58A o cable for micro 2 + shield
and the connector is this one:
http://telesputnik.lv/en/Connector-Micro-4/28/70/117
it is a good connector used in CB microfone radio with good re ability
Regards