PimentoUK

The problem with the 'multiples of 62mm' bit is that your cable is likely to be 1000mm long. Maybe it's more correctly multiples of 61.3mm - that's about 1/2" difference over 1 metre. So it's not practical to get the length correct, when the cable is many wavelengths long. And the [i]exact[/i] frequency used is somewhat unknown. The 2.4 GHz ISM band specifies 2.412 - 2.484 GHz as the 'nominal' channels; this gives half-wavelength values of 62.2mm to 60.4mm.

For HF/VHF radio gear, we're talking half-wavelength multiples of 1 foot or more, so there is a real chance of getting it 'right' . And also the real-world physical opportunity to fine-tune the cable ( shorten it, anyway ) at the antenna end.

Edit:
"Does this mean leave the shield on or strip it off?"
In this application, simply removing it is the practical solution.
The case for unshielding the inner-wire, but leaving the stripped outer attached, is when you want to make a T - shaped antenna feed. Where the co-ax is the vertical of the T, the two top branches are the inner conductor and the removed shield. This is not appropriate for a water-antenna, as encapsulating it in a water-tight way would be a headache, for a start.

No, don't consider it.
The exposed 31mm length ( in conjunction with the first 31mm of the shield ) acts as a centre-fed half-wave antenna. This in theory has an input impedance that is purely resistive at the intended frequency. This resistance is 50 Ohms, which matches the characteristic impedance of 50 Ohms co-ax cable. So maximum signal transfer from the antenna to the cable occurs. The cable is low loss at 2.4 GHz, so most of what 'went in' comes out at the other end - all you need to do is match it to another similar antenna, and the signal gets re-transmitted.
To be extra nerdy, the length of the co-ax cable matters, and it should ideally be multiples of half-wavelength long, ie. 62mm. It matters because the RF signal current flows in the inner core AND the outer screen.

( Anyone familiar with CB radio, for example, would know the ideal co-ax cable length ( rig to antenna ) is 18 feet in Imperial units ( 5.5metres ), and even if your vehicle installation only required 12 feet, you don't cut down the cable, just leave the slack in your trunk etc.)

Not all PI machines are expensive. Here in the UK, we have the C-Scope CS4PI:

https://regton.com/c-scope-cs4pi-metal-detector.html

But clearly it's not a nugget-hunter, they are mostly used on the beach ( though that is their target market , they are not waterproof, just the coil )

And of course some pinpoint probes are PI, and they don't cost 'car price' .

Apologies, I skimmed the thread, but ...
The length of the stripped section of cable should ideally be 31mm, which is a quarter-wavelength at 2.4 GHz. That then makes it an impedance match to 50 Ohms cable.

It's probably not going to be far 'off-spec' using 25mm / 1 inch, but the correct length may just give more leeway on antenna placement etc.

From a Europeans' view, it looks a lot like later Nuremberg/Low Countries Jettons. The 'decoration' around the border is an ornamental feature, loosely based on what would've been a real legible inscription. Sometimes they are referred to as 'blundered inscriptions' , just random letters/shapes in a pattern. The eagle is probably the spread eagle of Germany/Austria/Prussia that is depicted.
The holes in it are far too neat to be home-made, so I don't think it's a repurposed item.
My best suggestion is it's a button, that takes it's design cues from a late-1600's Jetton.
An example of a common-ish 'nonsense inscription' jetton is the 'Venus Penny':
https://finds.org.uk/database/artefacts/record/id/921901

And the French idea of decorative nonsense:
https://finds.org.uk/database/artefacts/record/id/887679

 

A discussion about this has just been started over on the Geotech1 forum. So far I've not seen any technical posts about it.
Another place to check on is "md-arena":

https://md-arena.com/wiki/minelab-manticore/

These guys like dismantling detectors, poking around to see what's new and different.

It sounds like you will need to get hold of a Bluetooth LE module that's similar to the WM08.
No doubt eventually such gizmo's will be made.
Failing that, buy some LE headphones, rip out the electronics, and re-house it all in a small 'project box' , with a stereo 3.5mm socket, and probably a higher-capacity ( longer-lasting) Lithium cell.
Tech problem : they use seperate electronics for each ear ... kinda complicates things.

I'm sure some of the more 'entry-level' detectors will have their microcontrollers programmed in assembler. Some may be a mix of compiled code ( often C++ ) and assembler.
For example the popular Microchip IC series:

https://www.microchip.com/en-us/products/microcontrollers-and-microprocessors/8-bit-mcus

https://www.microchip.com/en-us/products/microcontrollers-and-microprocessors/8-bit-mcus/pic-mcus/get-started-now

 

"I’ve always wondered why polycarbonate plastic (LEXAN) has not been used in an instance such as this? That stuffs tough !!!"

The Eqx coil is moulded from a Polycarbonate ( PC ) & ABS blend. My hunch is they used an inappropriate blend - too much PC , or not enough PC.
Plastic failure is not my area of expertise, but I recall stress-cracking to be a characteristic of PC, so if anything, I would speculate using less PC in the blend would be better.

"Also the coil cable is very thin at 2mm thinner than the superbly armored Nokta Simplex coil lead"

I assume the Simplex has a conventional coil, and coil cable. Meaning no electronic amplifier inside the coil. So it uses screened cable for the Receive coil wires, screened cable for the Transmit coil wires, and possibly another single wire for an electrostatic shield connection, maybe followed by an overall shield, then the outer sheath. That makes for a fat cable.

The Equinox ( and I assume the Mandingo ) have a pre-amplifier in the coil, with a differential output. So the RX cable doesn't really need shielding. There are additional wires, for a power supply, and a serial data link, but these can all be thin. The net result is the Eqx / Mandingo has a thinner cable.

The ears are long so that they can easily bend inwards when the bolt is tightened. The bending is spread over a longer length of material, not concentrated over a very short length, like on the Eqx coil ears.

Take a 12 inch plastic ruler. Fix one end, can the free end deflect two inches either way? Yes, easily, it's never going to break the ruler. Now take a 6 inch ruler, and deflect it 2 inches. It's straining the plastic more, and if you repeatedly bent it, you may get some cracking and failure.

I would've liked to see the carbon rod fit INSIDE the end-fitting, rather than the other way round. That would be a stronger solution.

I doubt that site is known at all in the English-speaking world. I discovered it several years ago while searching for info about my vintage Whites Coinmaster 2 / DH.

https://detecteurmetaux2.blogspot.com/2015/06/detecteur-metaux-coinmaster-2-d.html

I'm part-way through restoring it. I have it functioning correctly, I just need to put it back together, then take it for a spin.

It's good to see that you're getting out and finding things.
Do you get much older stuff ? I'm still waiting for you to post up some silver coins, no doubt the Vanquish is capable of finding them.

(sorry for off-topic )
@Midalake:
Did you read my custom Eqx shaft thread? There's some ideas contained in it that may help you get more from your current shaft.

https://www.detectorprospector.com/forums/topic/14805-my-compact-eqx-shaft-project/

Rather than considering it an alternative construction method, I feel it is the only correct way, and gives the greatest chance of achieving a coil that is truly CENTRE-tapped. Methods such as " Wind 29T, bring out a tap, wind another 29T " are guaranteed to result in a coil that has the 'centre-tap' some modest distance away from the centre. The total end-to-end inductance should be much the same for both bifilar winding ,and half-then-half.

As for performance improvements, it's hard to say, without knowing the rest of the oscillator circuit design. Some designs may tolerate 60% / 40% split in the tap position.
Also relevant is the fact there are three coils working together. If they were all closely matched in terms of centre-tap accuracy, the coil as a whole would be more consistent.

I found it modestly interesting, from a technical viewpoint.
If anyone is making this coil, I suggest winding the wire bifilar, that is two wires together. So for example the large winding would be made as 29 T of two wires together. Then join the 4 wire ends together so they function as a centre-tapped coil.

My only old Whites machine is a T/R from the late 1970's , so a league away from BFO machines and quirky coils like this.

Carl and George's geotech1.com forum would be a place where this info may be of interest, (though I've observed that BFO tech gets little mention.)

https://www.geotech1.com/forums/forum.php

With those resistance values, it appears that your 6.5" coil is probably a working coil for SOME machine, just not your GB2.

Do a density test on it. That will give a decent indication of whether it's plated brass, 9/10 carat, 14 or higher.
The method ( copied from elsewhere ):

A ) Place a small container of water ( 20 - 50 cm3 ) on your scales, and 'Tare' the readout to zero.
B ) If you're wanting the weight of the item, place it alongside the water container, and take the reading as indicated.
C ) Using monofilament fishing line / polyester sewing thread / very fine wire, lower the item into the water, so that it is just submerged, and not touching the bottom or sides of the container. Make sure there's no air bubbles attached. Take the indicated weight reading.

Reading C is the weight of the displaced water, which, because water has a density of 1.00 g/cm3 , it's also the volume of the water in cm3 .
To calculate the density, divide the weight in reading B, by the weight in reading C.

So for example, an unmarked silver finger ring: weight = 9.50 grams. The volume = 0.92 cm3.
The density calculated as 9.50 / 0.92 = 10.33 g / cm3 which is typical for Sterling Silver ( tech data usually gives a figure of 10.36 )

Reference densities:

Copper 9.0
9ct 10.9 to 12.7
14ct 12.9 to 14.6
18ct Yellow 15.2 to 15.9
18ct White 14.7 to 16.9
22ct 17.7 to 17.8
Sterling Silver 10.2 to 10.3

The Deus 1 also has the option of displaying a Polar plot ( of target ID vs. amplitude ):

http://www.amdtt.it/2013/01/deus-analisi-delle-funzioni-segrete-della-versione-2-0/

And there's also the two AKA Signum machines, which are MF and have some 2D graphical capability.

Diluted lemon juice, about 5:1 thru 10:1 would be a simple recipe. Brush regularly with a soft brush, like an old toothbrush.
If you want slightly more 'pro' and less 'kitchen' , use citric acid powder, diluted appropriately ( I can't say what mix ratios ) Citric acid powder is used as a cleaner, and also in home brewing & cooking , if that helps find a supplier.

Your mystery coin/button may be a weight.
If it were my find, I would give it a weak acid soak to remove the patina. Then evidence may show itself, for example makers marks, certification marks, etc.

European here.
You're looking for your Roman coins on ploughed/plowed land ? The Roman coins are there to be found because of the ploughing, bringing ( some of ) them within detection range.
A deep detector is not your primary weapon. .. one that can discriminate out iron ( or audibly allow you to distinguish it ), pluck out non-ferrous from among iron, with reasonably fast recovery, is what you need. Your Eqx is going to be just fine.

The hole is curious in itself.
Coins pierced in order to thread a lace etc through them would have a larger hole.
Coins pierced to 'void' them, for example demonetised ones, usually have quite obvious punch marks, usually near the centre.
A forgery may be tested by various means, scraping, filing, punching, bending; so it may be there for that reason.

Any idea what metal it is ? The dark patina is flaking off, not typical of silver tarnishing. But there's no obvious green verdigris type deposits, that a brass/bronze coin would have.

Europeans to the rescue?
The mystery coin is 'copy' of a Mary Queen of Scotland coin.
It reads: MARIA DEI G SCOTOR REGINA on the obverse.
( Mary, by the grace of God, Queen of Scotland )
The original coin would've been a gold coin, something like this 60 Shilling / 3 Scottish Pounds:

https://colnect.com/en/coins/coin/100043-60_Shillings_3_Pounds_Ryal_60_Shillings-1542~1567_-_Mary_Queen_of_Scots-Scotland

... or the smaller 30 shilling piece.

Whether it was intended to deceive ( maybe it was gold plated? ) or just a replica, to be used as a lucky token, or as a gaming piece, I don't know.

But it's worth looking into.

A bottle-diggers probe is certainly one possible tool/technique to consider. You could probably make your own, if you had some engineering skills. 1/8" diameter spring steel, braze a 'ball' on the end slightly larger than the wire. Search online for home-brew manufacture.

Also, using a detector: Use non-motion mode, with a large coil, with cache-hunting technique. Hold the coil 15" / 40cm above the ground, and walk slowly, holding the coil steady and level. With subtle height adjustment, the machine can be brought to the threshold, and very small changes in signal can be heard.
Good machines for this could include the Tek T2 / Fisher F75. The Equinox is OK, the self-calibrating pinpoint threshold gets in the way a bit.

What would these bars be buried in? That's a very important question. Mason/Kilner jar with steel lid? Steel box, like ex-army ammo box? Plastic food container?