WHITES DUAL FIELD COIL

[daverave]

Coil Large: 12 inches, about 30 cm, 2 laps about 2 meters.
Reel Girl 8 inches, approximately 20 cm, 2 laps, approximately 1.5 meters.
Total cat6 approximately 3.5 mtrs.
Attached photo of a coil, this cubhierta with plastic tape to give more to blindage separation.
The blindage not seen in the photo.
Jose[ATTACH]27070[/ATTACH]

thanks for the photo jose that has given me a clearer view of what the coil should be like....just 3 questions....what is the inductance and resistance of that coil cause only two laps...and can the ends be soldered directy together ???

[Dave J.]

Yes, there was a performance ratio of the coils (a lot of variations).
Particularly you in Oz should know, that large PI coils can't be used well in the highly mineralized gold fields due to high ground response. This is, where the seperated TX (large) and RX (small) PI coil will solve the issue. And it also solves the EMI noise problem as well.
The dual field coil on the other hand will generate a higher ground response in the inner coil section, which makes the detector prone to hotrocks and minerals on the ground surface.
The seperated TX/RX coil will pick up less ground response, less EMI noise and will still detect deep and shallow small targets.
Just think of a small ground loop coil.
Aziz

Aziz is correct on this matter, as Davor figured out earlier in this thread. The "dual field" approach used on the Fisher Impulse and later by White's has its advantages in saltwater environment use, but in a gold prospecting environment its disadvantages outweigh its advantages.

--Dave J.

************************

Here's a funny piece of history.

Back when we (Fisher) introduced the Impulse, we got an inquiry from a fellow in Australia who had heard some sort of rumor that PI was the hot setup for gold prospecting in hot ground. (This was before the Minelab SD's, I'm guessing that it was Eric's machines that had given rise to this rumor.) The guy wanted us to give him a freebie for field testing, with a promise that he'd publicize the results.

Our marketing guy told him this is a beach & scuba machine, we sell gold machines and the Impulse ain't one, and we simply flat out can't recommend it for gold prospecting. (Even back then, I understood the ground balancing issues relating to PI, having fielded both VLF-style reactively balanced and "early and late timing" balanced prototypes. The Impulse incorporated neither type of ground balancing feature.)

The guy in Australia kept insisting, so our marketing guy finally caved in and sold him one for half price on the condition that he give us a report on how it did or didn't work out for him.

Of course it turned out to be worthless for that purpose, the guy bytched not only to us but badmouthed us in Australia claiming that we'd burned him.

It was a lesson well learned about human nature. A mistake like that never happened again.

[Jose]

Coil Large: 12 inches, about 30 cm, 2 laps about 2 meters.
Reel Girl 8 inches, approximately 20 cm, 2 laps, approximately 1.5 meters.
Total cat6 approximately 3.5 mtrs.
Attached photo of a coil, this cubhierta with plastic tape to give more to blindage separation.
The blindage not seen in the photo.
Jose

[daverave]

The cable used is Cat 6 or Cat 5.
This cable is used for data transmission, is composed of 8 conductors of 0.5 mm in diameter, in the case of Cat 6 the diameter is slightly larger, between 0.5 and 0.6 mm.
Another may use this cable between these values (0.5 or 0.6 mm) corresponding to 23 or 25 swg of acuero to the table.
The blindage we perform with Scotch tape No. 24.
In the image below is an example of a mono coil.
Jose[ATTACH]26734[/ATTACH]

im going to buy some cat6 cable..im still confused as to the winding of the coil using cat6 cable.....if i make a 12 inch coil then each turn is 1 metre long x 16T....so do i wind 16 turns of all the conductors all 4 pairs of the cat6 cable ????

[Aziz]

Hi Aziz


I dont get much chance these days to prospect our goldfields, our ground is pretty tough, on some of our goldfields you can throw a magnet on the ground and it just clumps with magnetic material, I should make a video of that someday.

I as thinking more along the lines of the beach, to use a seperated TX/RX coil

Yep, the seperated TX/RX coil would be very convenient for heavy mineralized gold fields. Particularly for deep and large nugget detecting.
Cheers,
Aziz

[6666]

Hi Aziz

Particularly you in Oz should know, that large PI coils can't be used well in the highly mineralized gold fields due to high ground response.

I dont get much chance these days to prospect our goldfields, our ground is pretty tough, on some of our goldfields you can throw a magnet on the ground and it just clumps with magnetic material, I should make a video of that someday.

I as thinking more along the lines of the beach, to use a seperated TX/RX coil

[Aziz]

Hi Aziz
I dont have the XL sheet, so not sure if I will understand whats on it,
but from your experiments with the large TX coil and small RX coil
was there any ratio or size of the coils that looked good for experimenting with a dual PI coil?

Yes, there was a performance ratio of the coils (a lot of variations).
Particularly you in Oz should know, that large PI coils can't be used well in the highly mineralized gold fields due to high ground response. This is, where the seperated TX (large) and RX (small) PI coil will solve the issue. And it also solves the EMI noise problem as well.
The dual field coil on the other hand will generate a higher ground response in the inner coil section, which makes the detector prone to hotrocks and minerals on the ground surface.
The seperated TX/RX coil will pick up less ground response, less EMI noise and will still detect deep and shallow small targets.
Just think of a small ground loop coil.
Aziz

[daverave]

[QUOTE=6666;180087]Hi Aziz
I dont have the XL sheet, so not sure if I will understand whats on it,
but from your experiments with the large TX coil and small RX coil
was there any ratio or size of the coils that looked good for experimenting with a dual PI coil?[/QUOTE

i experimented with a whites coil cover and wound coils the same size....i tried two different gauges of wire for the 6 inch inner coil 30 & 32 swg but the 12 inch coil was 32 swg only....i would say that i got better proformance from my single coil...im getting about 15 inches in air on an old uk penny and 12 inches on a small 9ct thin section gold ring but depth not so good on medium iron which is good for me....ive lost interest now in dual field !!!!

[6666]

Do you understand the XL sheet content?

Hi Aziz
I dont have the XL sheet, so not sure if I will understand whats on it,
but from your experiments with the large TX coil and small RX coil
was there any ratio or size of the coils that looked good for experimenting with a dual PI coil?

[daverave]

lm confused im not sure what XL ?????

[Aziz]

Aziz
do you remember any details from your XL sheet ?

Do you understand the XL sheet content?

[daverave]

i think i will just stick to mono coils....cant really see the point of dual field when i can get the same proformance from my single mono coil....im not that impressed with dual field....i think better wire and lower noise levels and amplification is the way forward for a deep pi detector.

[6666]

Aziz
do you remember any details from your XL sheet ?

[bernte_one]

a separated tx/ rx combination makes sense for a pi
somes commercial designs use this for best sens to small objects

not the easiest type to build but also not complicated

[Aziz]

Well, I can not force you to use it. It's up to you to recognize the benefits of such a design.

But I'm almost ready for the mental hospital...

(That would be the sixth times this time... )
Aziz,
the madman