PimentoUK

I always thought the Equinox single frequency options ( 5/10/15/20/40k) were sub-optimal, so it's disappointing to see the same selection used on Mandingo.
The frequencies should ideally be a fixed ratio apart, and evenly spread over the full range.
So more correct values would be:
5 kHz / 8 kHz / 14 kHz / 24 kHz / 40 kHz
or
5k / 9k / 15k / 25k / 40k if you want 'rounder' numbers.
The relevant difference is the big gap from 20k to 40k is filled, and the too-small step from 15k to 20k is expanded. This may make the machine have a better nugget-shooting freq selection. Other differences are subtle; the choice of 8 kHz matches that of many high-medium conductor detectors, like the Tek Greek-series.
As Eqx/Mandingo can generate absolutely any freq in the range, there's always the option of more choices, in which case:
5k / 8k / 12k / 18k / 27k / 40k
would be good. Plus, being a premium product, Mandingo ought to have more choices than the Equinox.

Best guess, based on Deus 1 coils:
The same transmit coil is used for all modes, regardless of frequency choices. So the Inductance is fixed.
Inductive reactance, XL = 2 * pi * f * L
notice it increases with frequency ... halve the freq, the reactance halves. etc.
Current through the TX coil is: I = V / XL
where V is the amplitude of the ( assumed sinewave ) transmit voltage signal.

So, if you lower the frequency of the transmit waveform, the current through the coil increases. This increases the battery drain.

XP have taken steps that mitigate some of this, by using a more complex transmit signal ( DeepHC & Dive ), that has less low-frequency component , but it's still a power-draining choice.
See this thread:
https://www.detectorprospector.com/forums/topic/18707-not-much-chat-about-multi-frequencies/?do=findComment&comment=198887

It also affects other selectable freq machines; NokMak mention it in the Impact manual, for example. No doubt the Deus1, and the Equinox run at 4 or 5kHz will be affected by it.

I use some 'sport' earpieces, that have the hook going behind the ear to secure them, but the speaker element is 'large' ( actually 14mm diam ) and simply points at the ear canal, and doesn't go into it. They seem comfortable for long-time use.
Sorry I can't come up with a brand/model , but based on the description, you may be able to find something similar.

It's nice to find big silver, even if the silver quality is lacking. I've not found many half-crowns myself, and I'm sure all were 50%, the older Sterling ones have eluded me so far.

If you didn't know, 50% silver coins clean up well with a soak in a weak acid solution. An example being diluted lemon juice, approx 5 : 1 dilution ratio. Brush with a soft brush occasionally.

Correct, it's not discussed there.
I don't actually know what the difference between the two is. I was under the impression 'subtractive' was the 'normal' MF technique, and so the mention of additive intrigues me.

Suffice to say, the designers think it's best for the particular circumstances, so just get on and use it.

Dive mode is a multi-freq mode that's heavy on 4.8 kHz, so it's not going to be all that hot on 'low ID' targets.
Presumably the designers chose the 4.8k / 14.3k frequencies as they are less affected by salt water than a higher-freq mix.

Here's the freqs used in the various D2 modes:

https://www.detectorprospector.com/forums/topic/18707-not-much-chat-about-multi-frequencies/?do=findComment&comment=198887

"I was hoping someone like RNB made an even better one"

I doubt you will get one much better, a small amount is possible. Minelab have used a good quality cell in the Equinox, 5000 mAh is at the top end of capacity for a 26650 size. I have seen 5500mAh quoted from Vape and flashlight manufacturers:

https://www.ecoluxshopdirect.co.uk/soshine-26650-5500mah-battery-protected

https://www.orbtronic.com/26650-battery-protected-li-ion

These two are protected, unprotected cells are what you really want, especially considering the space aspect - protected cells are typically 1mm longer.
Anything claiming over 5500 mAh is most likely fraudulent, especially if the 'brand' is UltraFire/SuperFire/CatchOnFire etc.

Bowden cables are also used for the throttle control on petrol ( gasoline ) lawnmowers, which are obviously used on a sports field.

This interests me for a few reasons.
A couple of years ago, the subject of Sunray coils, and how they work, came up over on Geotech1 forum. I was working on building a version for my F75, which might also be duplicatable as a self-contained mini-detector.
But I also realised that my Equinox could also be suitable for a 'Sunray' ... for one special reason. Everyone knows the Eq has a 'security' chip ( and some other electronics gubbins ) inside the coil ... hence no aftermarket coils. But the key feature of a Sunray probe is that the original coil is STILL ATTACHED . This permits the trick of using the 'security chip' of the main coil, while connecting the Sunray probe coil windings up to the detector.

It's still quite a job to make a coil like this for the Eqx, so hats off to the engineers who did this. I never progressed to designing my own .. it was going to be larger, probably about 2.5" diameter.

The 'mystery item' looks like the ferrule fitted onto the end of Bowden cables, for example bicycle brake cables. Similar cables are used on automobiles, too.

And it also shows the plateau of signal strength at close distances that mono coils show. If that were reproduced for a DD, the blue trace, for example, would keep going up, to 100000 ( very approx ).

Simply put, when a target is in the middle of a 10" mono coil, it's still 5" away from the nearest coil winding. Whereas a target in the middle of a DD is just 1/2" or so from both TX and RX.

Carl: The graph I was thinking of was prepared by Mr.Green, in a thread related to finding the optimum coil size for a given target/depth. We discussed Eric's semi-circular graphs, and then Green used the 'Hyperphysics' website to analyse a mono coil. When all the maths misunderstandings were sorted out, the result was a neat Excel plot.
This is the thread, post #39:
https://www.geotech1.com/forums/showthread.php?24020-detection-depth&p=237587#post237587

"I charted distance vs amplitude with Hyperphysics for a 200, 300, 400 and 500mm coil to see if that would help determine best coil size.
Her's an attempt at charting the coils. Example: a 200mm coil can detect a target at 400mm, what diameter coil would detect the target the greatest distance? The 500mm coil has the same signal amplitude at almost 600mm distance. A target just detectable at 100mm with the 200mm coil wouldn't be detected with the 400 or 500mm diameter coils at any distance."

[when I get on a newer computer, I'll edit this post with the graph, and sort out the hyperlinks. This ever-changing forum keeps outsmarting my browser]

That graph shows this not-too-intuitive phenomenon quite well.
It also applies to PI machines with mono coils. And it's possible to calculate mathematically the behaviour of mono coils fairly easily, so it can be shown in a theoretical way, as well as physical measurements on a real detector. There are some discussions over on Geotech1 forum where charts like the above were posted.
PI's do see the ground differently. From some discussions on Geotech1, I recall Eric Foster stating that PI's pick up the same level of ground signal regardless of coil size.
And a mono coil has quite different behaviour to DD's ( and CC's ) when the target gets close , ( below 1/2 of the coil diameter away ). Essentially, the signal strength plateau's at close distances, whereas for a DD, it continually increases ( in practice, until the target touches the coil housing).

Quote:"So ... you say a small coil will have trouble to detect bigger items?"

Yes, a small coil will give a smaller signal than a 'standard' coil, on a large target. And a large coil will give a larger signal than the standard coil on that target.

Roughly: Going from a 10" coil to a 5" coil will result in 1/6th the target signal. But ground signal strength will be down by a half, so there's the possibility of increasing gain and/or sensitivity, to leave you with a 1/3rd drop in signal. This would equate to 80% of the standard coil depth.

Quote:"Thanks for trying to explain Induction Balance"

I didn't explain it. I did point out there are engineering design constraints for small ( and large and standard ) coils .... the designer can't simply wind three times the number of turns on a small coils' loops to make up for the loss of signal, because the result would be incompatible with the detector.

Quote:"could you please explain this? : "small coil has .. less sensitivity on big targets""

On a VLF machine, the precise inductance and resistance of both coils ( transmit and receive ) is important. Hence all coils, small or large, for a given machine need to have exactly the same inductance & resistance. This then determines how many turns of wire go on the TX & RX coils. This combination of different size loops, different number of turns, affects the strength of the transmitted magnetic field, and the sensitivity of the receive coil. A smaller coil simply gets a smaller signal from a target, so the target needs to be closer to be detectable. Vice-versa for the larger coil.
On the plus side, a smaller coil also picks up a smaller ground signal, which helps the detector pick out the 'target signal' from the 'ground signal'.
Other relevant factors include: Does the detector know it has a small / large coil fitted ?
If it does, then small changes to the way it operates, such as gain/sensitivity changes, ground filtering characteristic changes, can be made, to mitigate the effects of the new coil. Machines that will almost certainly do this include XP Deus/Deus2, ML Equinox, XTerra's. But the majority don't, and it's down to the operator adjusting sensitivity up/down etc to make the best of a different coil size.

Here in the U.K , some archaeologists are very critical of metal detecting. One reference article used when assessing the prevalence of detectorists is this Hardy article:

https://www.tandfonline.com/doi/full/10.1080/23311886.2017.1298397

I haven't given it more than a quick scan, it may have worthwhile info in it.

Ploughed land is indeed difficult, for several reasons. And it's difficult to reproduce, so it's not surprising that no-one talks about depth in such ground.
Depth tests are mostly relevant to flat, undisturbed ground; public parks; pasture farmland; woodland; grazing land. But these are where targets can be, and often are, deep. And the deep targets are potentially the desireable ones.

I'm not enthusiastic about 'test boxes' either. They need to be pretty large, especially for most single-frequency machines, that use filtering to help seperate ground-signal from target-signal. Multi-freq machines are not so dependant on this ( I think ), relying on measuring the ground at two ( or more ) different frequencies to largely reduce ground signal.

Also, real ground is compact, which is hard to replicate in a box. When I buried my test-garden items, I used a lump of wood ( 2" x 2" / 50mm x 50mm) to pack down the soil in 2 inch layers as I refilled the hole, ensuring there was minimal inconsistency in the site. I didn't want my machine false-detecting the hole, nor the opposite effect, suffering reduced performance due to ground-signal fluctuations.

Yes, the ground is the BIG variable. Some testers go to some trouble 'sanitising' their test ground ( removing stones, levelling the surface ..) which has the effect of making it easier to detect targets.
Plus ...no-one has any equipment to truly MEASURE the ground characteristics, not with any useful accuracy. Plus, it's moisture-dependant, affected by what frequency you choose to measure it at, and not forgetting VLF's and PI's see things differently...

I personally don't think air-tests are that useful, except for comparing MY nugget-smasher2001 with Bob in Australia's one.
It's pretty easy to modify most detectors to give more air-depth ( increase RX amplifier gains for example ) but they won't produce gains in-ground.

Quote:"The purists will tell me you have to compare the same element ...."

Yes, that's the whole idea of a 'standard' target .... you use the same target, then the results become usefully comparable. Substituting a 'modern' .900 fine ( ? ) Napoleon coin with a 2000-year old quarter-stater made from electrum ( natural gold/silver alloy ) is not worth doing.

I have to say that using ANY gold coin as a 'standard' is a poor idea. Test standards need to be low cost, or very low cost, so that anyone can readily obtain them, or several of them. I would be wanting a couple of 'test garden' ones, buried at decent depths, in different locations; maybe one tilted heavily; one for air-testing; a spare to take out in the field for impromptu in-ground tests. If they cost more than 5 US dollars, they are too expensive.

Tom Dankowski seems fond of using a 1 Dollar US coin from the 1850's as a 'difficult low conductor' test standard. Not only is it gold, it's old and collectible, so commands a price premium over it's bullion value. I went to the trouble of designing and making a 'fake dollar', that was pretty close to the real thing, and could have been reproduced by anyone with some engineering skills.
A better idea is to choose a circulating coin that has comparable characteristics to a small gold coin. There's plenty of small cupro-nickel coins worldwide; my 'favourites' include the Norway/Sweden 5 Ore from the 1980's ; the New Zealand threepence from the 1960's; the UK sixpence from the 1950's/60's; the UK 5 pence from 1990's/2000's.

Quote:"I don't know how there can BE a "decay" if there is no "break" in the transmit"

The FBS waveform consists of a burst of 8 cycles of 25kHz ( taking 320 microsecs ) followed by one cycle of 3.125 kHz ( taking 320 microsecs ), then repeat. Note: these are NOT sine-waves, they are SQUARE waves, of 50/50 duty cycle.
The single cycle of 3.125kHz is split as quarter-cycle / half-cycle / quarter-cycle. This middle half-cycle is, I assume, where the 'Pseudo-PI' / time-domain stuff takes place, there is a 160 microsec 'break' , long enough to make use of it.
This doesn't exist on the SMF Equinox waveform, there's barely 10 microsecs before the next edge transition, thanks to the 39kHz component of the transmitted waveform.

Economics? The general public want it cheap, so industry-standard Imperial sized aluminium tubes are an obvious choice.

But you have a point about the packing aspect. Even with simple tubing, they could put more thought into the design. There's examples of machines that break down into 3 sections ... that's good. Except one is long, one medium, one short .... not really a recipe for optimum packing.
I've also noted that other aspects of the mechanicals are poor, too. Making two huge 13mm diameter holes in a 22.2mm tube is awful engineering, especially at a high stress point. But two manufacturers have done this. And both have seen failure of the tube as a result.

But, how do you know they DON'T optimise ?
Modern machines like the ML Equinox have a 'security chip' that would/could identify itself as:
"Genuine Minelab 11 inch DD coil here". This info is read by the main control-box brains, so there's no reason it couldn't adjust to compensate ... increase the 'gain' on a small coil ( decrease on a large ) ; use different depth gauge calibrations so they stay true regardless of coil size ; change recovery speeds, maybe, or filtering time-constants.

And obviously, the XP Deus coil has plenty of electronics and micro brains inside it as standard, so clearly it knows if it's a 9" elliptic DD etc, it's programmed into it during manufacture. Hence a large coil can be programmed with data about gain settings, or possibly the analogue side of the electronics has a few component changes affecting amplifier gain.

However, it's pretty obvious that most machines don't have this ability. Any machine with a 'dumb' coil, with no integral amplifier or ID micro-chip/serial ROM, is unlikely to be coil-type aware.

However, some of the older Minelab's, like the Sovereign, etc have a pre-amp internal to the coil. There's no reason why the gain couldn't be modified to suit the coil size/shape. They have been reverse engineered, so the info is out there ... perhaps the electronics is identical between coils, I haven't studied the details.

I hear the new machine's successor is to be called the Diamantecore.

As well as having some extra technical features, it is decorated with Swarovski crystals.

Re: the Pseudo-PI technique used on FBS machines, this thread should explain:

https://www.detectorprospector.com/forums/topic/13202-ctx-4040-or-equinox-1000-or-both/?do=findComment&comment=133265