PI Mono Coil Cable question

[Polymer]

Sommer Spirit LLX

52pF Shootout 'Black Powder' Cables!

Van Damme Silver Series Session Grade Lo-Cap

55pF

Best-Tronics CA-0446

66pF

Connectronics Rockflex

66pF

George L's .155

67pF*

George L's .225

67pF*

Hosa CGK

68pF

Klotz AC110

70pF

Mogami 3368

70pF

Gepco XB20UB

73pF

Sommer Stratos

75pF

Klotz Titanium

75pF

Sommer Classique

78pF Shootout 'Shooting Jacket' Cables!

Sommer Spirit

78pF

Sommer Corona

78pF

Cordial CGK 122

82pF

Sommer Tricone XXL

85pF Shootout 'Boot Hill' Cables!

Sommer Tricone MKII

85pF

Sommer Spirit XXL

86pF Shootout 'Gun Smoke' Cables!

Cordial CGK175

88pF

Cordial CGK Road 75

88pF

Van Damme Pro Grade XKE

90pF

Van Damme Pro Grade Classic XKE

90pF

Van Damme Silver Series Session Grade Flat-Cap

90pF

Adam Hall KIK122

95pF

Klotz AC106

95pF

Proel HPC140

105pF

Hosa Zaolla Silverline

105pF

Klotz AC104

115pF

Whirlwind Accusonic+1

115pF

Conquest Sound USA 1

115pF

Conquest Sound TL

115pF

Proel HPC110

120pF

Proel HPC130

120pF

Adam Hall 7115

122pF

Van Damme Silver Series Session Grade Hi-Cap

125pF

Sommer Colonel Incredible

130pF

Mogami 2524

130pF

Cordial CIK 122

130pF

Gotham Audio GAC-1

146pF

Belden 9778

148pF

Canare GS-4

154pF

Mogami 2319

155pF

Canare GS-6

160pF

Free The Tone CU-416

160pF

Belden 8412

190pF

Guitar Cable

Capacitance (Signal Core to Shield per Metre)

[godigit1]

Ok thank you for that Polymer.
I didnt understand what Eric said about the black conductive layer but when you described it the picture formed in my mind sure enough I have used this and have tested several coils using this wire. All were decent but now I know why my first detector Surf PI kept blowing Ics. I had used this wire striped out of a cable for all my attachments . i thought hey double insulated why not. Never thought to check it for conductivity.
I now have several coils to revisit I had made a test cable out of it as well.
So the Hosa tech Mic cords from Best buy no good . Have a diaderio high end I havent cut into yet.
But one good thing about the Hosa is you can pull the wires directly out leaving the copper schield intact. Then either fish your own leads through or Im going to try to pull the belden cable I mentioned above through its about the right diameter.
This would be both the propritary beld schield and a traditional copper mesh schield for a triple schield beacuse beldschield is a two layer seperated by a dilectric.
Do you guys think this would be good or is it simply overkill?

[Polymer]

Ok thank you for that Polymer.
I didnt understand what Eric said about the black conductive layer but when you described it the picture formed in my mind sure enough I have used this and have tested several coils using this wire. All were decent but now I know why my first detector Surf PI kept blowing Ics. I had used this wire striped out of a cable for all my attachments . i thought hey double insulated why not. Never thought to check it for conductivity.
I now have several coils to revisit I had made a test cable out of it as well.
So the Hosa tech Mic cords from Best buy no good . Have a diaderio high end I havent cut into yet.
But one good thing about the Hosa is you can pull the wires directly out leaving the copper schield intact. Then either fish your own leads through or Im going to try to pull the belden cable I mentioned above through its about the right diameter.
This would be both the propritary beld schield and a traditional copper mesh schield for a triple schield beacuse beldschield is a two layer seperated by a dilectric.
Do you guys think this would be good or is it simply overkill?

Here a photo of the culprit, just to complete the picture ...

Can you post a picture(s) of what type of cables(s) you mean in the last paragraph, I can't quite follow what you mean.

[godigit1]

Yea there you go. Same black crap.

Here is a picture of the cable I was using.


In the other photo I have pulled the wires and shield out of the cable. I placed the belden 110 ohm cable in the middle.
you can see the belden cable is pretty close to the same diameter. so what I was saying is you can pull the bad wires out with a fish line pre attached and that way you can pull whatever you want back into the shield. within reason of course. Good way to shield if you want to use solid coil lead wire to the pcb. One thing I did do is test this shield and even though it is pure copper it does not detect well on a PI. A eight inch peice is only detectable if I wad it up if I remember correctly it was a few years ago. and that was a stock surf pi.

The beld shield I refer to is in this link or if you look around you will find a little info on it. They do have a 4 wire version of this cable where both sets are shielded form one another too. https://catalog.belden.com/index.cfm...=pd&p=PF_1800B

[Polymer]

Yea there you go. Same black crap.

Here is a picture of the cable I was using.
[ATTACH]46202[/ATTACH]

In the other photo I have pulled the wires and shield out of the cable. I placed the belden 110 ohm cable in the middle.
you can see the belden cable is pretty close to the same diameter. so what I was saying is you can pull the bad wires out with a fish line pre attached and that way you can pull whatever you want back into the shield. within reason of course. Good way to shield if you want to use solid coil lead wire to the pcb. One thing I did do is test this shield and even though it is pure copper it does not detect well on a PI. A eight inch peice is only detectable if I wad it up if I remember correctly it was a few years ago. and that was a stock surf pi.

The beld shield I refer to is in this link or if you look around you will find a little info on it. They do have a 4 wire version of this cable where both sets are shielded form one another too. https://catalog.belden.com/index.cfm...=pd&p=PF_1800B

godigit1, weren't you happy with the first cable you were using? Looks like it has a spiral shield, as opposed to a braided or foil one.

If I got this right you are removing the foil parts of the belden cable? If not, have you tested the foil with the PI you'll be using?

Not sure if a test with a stock surf PI you once did is valid as to the 1st delay time with a home brew one. Yours will likely have a shorter delay time.
That can make a world of difference with foil stuff as I have seen myself - squealing PI when foil bits get anywhere near it.

You were asking about overkill ... Hmmm ... what are you trying accomplish?

[baum7154]

Regarding posts 3,5,& 6 of this thread I completely agree with the use of a continuation of the coil wire on a 3DSS COIL to achieve a minimum feedline capacitance in the range of .9pf/inch. This technique also removes any solder joints from the coil which might otherwise be detected at short sample delays. Attached below is my post on this topic from 8/28/2013 in a thread titled Chance PI Coil. I recommend any one interested in the 3DSS COIL read this thread even though at this early time I incorrectly called it a ?spider coil?. Some time later I gave it the designation of 3DSS which stands for: 3 Dimensional coil wind, Self Shielding

I never liked the use of coax because of the significant capacitance it added as I was building for small gold detection.

I will try to post some construction photos from the same thread for those interested.

Regards and happy building.

Dan

• 8-28-2013, 09:04 AM
  #22
  
  baum7154
  Guru
  
  
  
  Join DateApr 2011LocationColoradoPosts1,002
  
  
  
  A wider and modified version of this coil is what I am using on my Chance detector. I used 32 turns of 26 AWG silver plated, stranded 600 volt teflon insulated wire on a 1.050 wide, .093" thick 8" OD. Lexan form with the slots machined .400" deep from each inner and outer edge. The feed line is a continuation of the coil wire 33" long and twisted at a rate of 3 twists per inch. This results in a 335 uh coil.
  
  The system ground is connected to the wire end of outer winding and this results in what I believe is a degree of self shielding due to the geometry of this coilconstruction. I used 4 each lengths of 3/8" urethane foam 'Backer Rod' and 1/4" thick x 1/2" wide strips of urethane packing foam to fill out the cross sectional profile of the coil. The Backer Rod and foam strips were over wrapped with Curity self adhesive cloth hospital tape, using a 50% tape overlap on the inner part of the form. Consistent tape wrap pressure was used to avoid crushing the profile. Then at least 2 layers of fiberglass mat and resin were applied and a Lexan cross support with Lexan mounting ears were glassed in across the lower third of the assembly.
  
  Initial critical damping of this coil performed with the coil suspended on the boom in the air required 1040 ohms in order to get the unit to operate down to a Guard Interval setting of '10'. While detecting a 1/2" SQUARE aluminum target on the ground I noticed that a damping resistance of 980 ohms gave the best signal strength. However the unit would not operate in open air at a '10' GI setting with that resistance value, it was just on the threashold of operation. I re-ran the damping adjustment in air last night and ended up with 1110 ohms and good overall sensitivity while achieving good idle state quietness of the detector i.e. just a few occasional beeps. Will test with the foil target on soil this evening to see what the impact to signal strength has been.
  
  All of this leads up to my perception that bringing the earth/capacitance into the picture appears to lower the self resonant frequency of the coil and results in reducing the optimum value of the damping resistance. Has anyone addressed this issue in a different process for determining critical damping resistance? Otherwise I believe that setting resistance in open air does result in some over-damping of the coil when it is in use close to the earth. I do recognize that 'Earth' effect on a coil is highly variable so maybe damping in open air is the best we can do.
  
  Regards,
  
  Dan
  
  
  
  
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[6666]

Hey Dan have you found any small gold ?

[green]

baum, have you measured the SRF of the coil reply #51?

[baum7154]

Hi 6666,

Hope you are well and finding lots of nuggets.

I’m at a place in life where the grand children are growing up enough to go out slucing and
prospecting and a bit of detecting. We went once last year to a place that was pretty good 25 years ago. Guess what, now it is posted and in private hands so we had to settle for a roadside right of way access not too far away. It did turn out well though as we did get a small amount of flakes in a glass vial for my oldest grand daughter. Now she is hooked and eager to go again and a year older. I’m eager to get back out too. Have my eye on a historical hydraulicing area about 100 miles out that I’d love to detect. Hopefully this summer it will happen. Retirement is not far off and that will free things up too.

Regards and happy hunting.

Dan

[baum7154]

Hi Green,

Its good to hear from you again. I see you are still providing workmanlike support to this group! I hope you are doing well.

Yes I’m sure I measured this coil SRF a long time ago. I’ll have to look it up and get back to you here.

Regards, back to you soon.

Dan

[baum7154]

Green,

the SRF of this coil AND 33” feed line is 1.056 MHz

dan

[godigit1]

godigit1, weren't you happy with the first cable you were using? Looks like it has a spiral shield, as opposed to a braided or foil one.

If I got this right you are removing the foil parts of the belden cable? If not, have you tested the foil with the PI you'll be using?

Not sure if a test with a stock surf PI you once did is valid as to the 1st delay time with a home brew one. Yours will likely have a shorter delay time.
That can make a world of difference with foil stuff as I have seen myself - squealing PI when foil bits get anywhere near it.

You were asking about overkill ... Hmmm ... what are you trying accomplish?

No just the opposite. The cable I was using has the conductive black layer on both wires.
What I was talking about doing is using the Copper schielded cable after removing the inner wires. This leaves the schield completly intact and a very nice cable left to work with.
Then I was talking about either pulling the belden cable through the copper schield, In essence combining both schielding techniques
The propritary Beld shield Plus a standard copper mesh shield.

The other possibilty if for schielding continious leads from the coil as Dan is talking about in post #51
Using supplys Like this Ptfe tubing and expandable sleving one can make a very nice lead wire assymbly to pull back into the copper shielded cable.


As far as what I trying to accomplish? A good way to make a cable immune to noise without signal loss.

[green]

Green,

the SRF of this coil AND 33? feed line is 1.056 MHz

dan

Thanks

[baum7154]

Oh and it is 334 uh

[godigit1]

Someone needs to start a thread to specifically to talk about coil types wire types and their relationships to SRf. Everyone could record data there and we would have one specific place to look for info on design potential of the different coil configurations and their application for use on specific target Tc catagories.\
Hint Hint.
I cant think of a better person Green since you have been working with this extensiveley .
That and you have a wonderful way of presenting data.
Just thinking Planting seeds.
Best Regards