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Offline xavier
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« Reply #30 on: May 07, 2010, 04:09:30 am »
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Hi GD

Thanks for this valuable information interesting that the reception will be better I'm also going to make dual spiral coils latter on
this coil if for a PI detector I did check the inductance with a meter I get 865uH so what I thought of doing was make a second coil scatter wound measure the inductance and then mach it with the flat coil the length of wire that I used is the same. The reason why I want to make flat coils is because I want to build Gary's pulse 2 and his design has flat coils (I'm also busy building the DBP2010 at the moment) you may use scatter wound coils too but they don't work as well. But the proof is in the pudding and I'm having a lot of fun doing this plus I'm finding out new things lot's of new things  Smiley 

Regards Xavier

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« Reply #31 on: May 23, 2010, 11:35:20 am »
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Hey Guys,

I just got done building a Pulse-1 myself; I'm still testing it so I don't have much to comment on it's performance (plus it's my first MD, so I have no comparisons).  I've seen very little discussion about building Faraday shielding for PI coils (I guess because they are less susceptible to ground effects?), but I am curious if anyone has any results using shielding on a flat coil.

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« Reply #32 on: May 23, 2010, 03:22:48 pm »
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Hi magnetman

If you take a look at Gary's PI you will see that he has a shield on his coil basically you must insulate your coil then you may use some tin foil to shield it all that you must remember is to leave a gap in the shield, you do this on both side's of the coil. I insulate my coils with a thin coat of epoxy(I only do this on my flat coils)  then do the shielding after I do some test's and if all is well , one more coat of epoxy and the coil is ready.   

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« Reply #33 on: May 23, 2010, 04:20:11 pm »
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Hi xavier,

My coils are definitely insulated with epoxy.  Without it, they would vibrate a little creating all kinds of electronic noise.  Does shielding the coil make a an appreciable difference in performance?  Also, since I am using shielded audio cable (foil wrapped with braided copper strands) would the coil shield be tied to that?  Lastly, since my enclosure is tied to ground (as well as the negative pole of the coil jack), should I tie the shielding to the enclosure?  Right now, none of the shielding is tied in and I get very little noise.

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« Reply #34 on: May 24, 2010, 04:20:24 am »
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OK let me see if I got all of this 1) you are using audio cable for the coil? if yes then there is no need to shield the coil as you already have a shield in the cable so there would be no difference at all (I use magnet wire so I have to shield) 2)Now if I got it all wrong and you too are using magnet wire for the coil then you should have the coil shielded and connected to the cable shield that goes to the electronics and then connected to your ground You do have a ground on the pulse one if I remember correctly he used a positive ground and not a negative ground (check it on your schematic) I don't think that placing a shield on the PI does much of a difference I have never seen the pulse one coil with a shield on it in fact I have a VLF that I build and I don't use a shield on the coil as I find that I have a better response with out the shield than with the shield what you could do is use some aluminium foil to shield it and then do some tests but do them out side once you have done your testing rip off the shielding and do them all over again now you will be able to say whether the shield is beneficial or not I once spent two days adjusting and sorting out all my problems only to find out that I had done it all for nothing once out side it did not work at all (I don't do any setting up inside any more) I hope that this will be of help to you.

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« Reply #35 on: May 24, 2010, 09:58:07 am »
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Hi xavier,

I used magnet wire for the coil and shielded audio cable for the connection between the coil and the electronics.  (I reread what I posted and it certainly was confusing!)  The coil is a handrolled concentric.  20 AWG, 34 turns, OD 8.25".  At this point I am just looking for optimizations.  I have a jar full of rusty hardware dug out of my backyard, so I know it works!

Thanks,
MM

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« Reply #36 on: May 24, 2010, 10:58:35 am »
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What depth are you getting out of it I know that this is one of those boring questions and that it depends on the size of the object but if you are happy with depth and stability also if you don't have noise then why bother. I went and had a look at the detectors that have been build by different people all over the globe and non had a shield on the coil (flat coils) yet I'm convinced that when I read Gary's article he did have a shield. Mind you on a concentric coil it would be very easy to do a test to see if there is any improvement. I see that you used 8.25" OD  according to my calculations you should have 29 turns using 20 AWG and you have 34

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« Reply #37 on: May 24, 2010, 11:38:23 am »
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Hi xavier,

I'm getting a range of between 8" and 10" for an American quarter (1" coin) in air.  Maximum distance is almost 3' for very large objects.

I did my best to follow Gary's parameters for coil winding.  I was shooting for his 8" OD coil.  He suggests 5.8" ID, 20.5 AWG, and 34 turns.  I figured that I had about 10% wasted space and there is a little difference in the diameter of 20 AWG which resulted in an outside diameter of 8.25".

I wrote to Gary and he told me that the specifics of the coil design were not critical as long as the right size coil is selected for the right type of targets.  I also didn't see any discussion on his page about matching the electronics to the coil.

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« Reply #38 on: May 24, 2010, 01:38:02 pm »
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 Grin Grin I think that making coils for the PI is like battle ship Hit or miss when you hit it works very well and when you miss it works. Perhaps what you should do is close it all up nicely and go out hunting with it then you will find out all the nity grity things that are good and bad from there you will have a plane of action for the next one that you build I take it that you will build another one in the future?

Regards Xavier 

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« Reply #39 on: May 24, 2010, 01:46:44 pm »
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Hi xavier,

I can certainly understand what you mean by hit and miss.  Looks like I have been lucky so far.  I opened a new thread with pictures because I don't want to hijack someone else's thread.  I also definitely agree that making a few field tests will be the best way to improve performance on future builds.

-MM

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