Pi figure 8 coil to cancel salt water response ... possible ... or not

[Altra]

Thank you. Found a few relatively simple ones. Here a pdf of some.
[ATTACH]50421[/ATTACH]

Mickstv audio circuit uses an absolute value circuit. MdToday did a nice redraw of the schematic in this link.

https://www.geotech1.com/forums/show...ighlight=micks

[6666]

The 24AWG wire for the pulse detector coil is too thin.

I made the coil out of 24AWG multi strand wire so it was easy to twist, are you referring to the resistance ?

[6666]

Hi 6666
Wondering why you are making it folded instead of two round coils(reply 6)inductance for the two coils would add.

Hi Green, well it was speed of manufacture mainly, I am interested to investigate the twisted fig 8 by its self and how much it reduces the emi that I have here, and I wanted to check a couple of other things with making a twisted coil, I may make the two separate coil type later .

From Eric from ten years ago

There are two types of figure 8 coil, one is where the TX/ RX winding is the same and just wound as a figure 8. The other is a separate TX and RX , where the RX only is a figure 8. Both perform rather differently. Both cancel em noise, but only the latter minimises the ground signal. The TX/RX figure 8 has a more horizontal field pattern under the centre of the coil, so it range is less than a mono, but the fact that you are free of noise means that the RX gain can be cranked up to win some of the loss back. This coil is not good for coins and rings, because they always give a minimum response under the coil centre for horizontal targets. However, for nuggets that have some thickness it could be a good coil. Interestingly, the German Vallon mine detector uses a figure 8 truncated elliptical coil (see their website).

The separate TX with separate figure 8 RX, is what Coiltek call a salt coil. The two halves of the RX give plus and minus responses, which cancel if they are equal. Hence good ground rejection and noise rejection. However, when going over a metal target the response flips from a positive to a negative as the crossover goes over the targets. Range on deeper targets tend to cancel too.

Eric.

[surfdetector]

The 24AWG wire for the pulse detector coil is too thin.

Eddy,
What size wire do you suggest?

[Melbeta]

No idea, don't think I've ever seen one.

.
Okay, got a photo of the Jack Roach Figure 8 coil, which he contracted with Semtech, and it came out as Semtech Metal detector SI model, with two holes. Top hole is Non-Ferrous target, hole nearer the case unit is Ferrous target hole. When George Payne came out with 1975 Whites VLF then Semtech ceased production and sales as the hand writing was on the wall.

I wanted to post a photo, but I cannot figure out how to add a photo into it and gave up... Something does not appear and let me attach a photo.
Melbeta

[Melbeta]

No idea, don't think I've ever seen one.

.
Okay, got a photo of the Jack Roach Figure 8 coil, which he contracted with Semtech, and it came out as Semtech Metal detector SI model, with two holes. Top hole is Non-Ferrous target, hole nearer the case unit is Ferrous target hole. When George Payne came out with 1975 Whites VLF then Semtech ceased production and sales as the hand writing was on the wall.

I wanted to post a photo, but I cannot figure out how to add a photo into it and gave up... Something does not appear and let me attach a photo. Not sure what I did, but somehow it attached. How do I clear all of the past photos from uploader???
Melbeta