Geotech

I've never seen a screen cover "go bad." However, the display might. It's not clear when you say "the face don't light up very well" whether you mean the backlight isn't working well or the display itself is faded. But both can happen. Also, indoors it can be hard to read without the backlight. So first, I would take it outside or make sure the backlight is on. Next, I would pop off the pod faceplate (it snaps on) and look at the screen without the screen cover.

5 hours ago, Steve Herschbach said:

But maybe we are just talking semantics. What you think of as a hole and I think of may be different things. To me a hole occurs when a detector will not pick up a nugget it should pick up due to whatever ground canceling method is in use also knocking out the gold target.

In a detector with only a single GB channel (like the TDI), it is possible to find a small range of conductivities at the conductivity transition point that are severely suppressed. When I air test the SDC with a continuous array of conductive targets, I can easily find the two transition points between the three regions. I could not find any range of suppressed targets with the SDC, target detection through both transition points was quite good. This tells me that the mathematical target holes are filled in.

Again, that's in air. If particular targets are then lost in particular ground, then that could be due to the way the tracking algorithm is working, rather than the mathematical target hole. I suspect the same thing would happen in a multiperiod detector. In other words, you can eliminate the mathematical target hole with either multi-TX or multi-RX, but you will likely still face the same issues with certain targets in certain ground. I can see calling that a "target hole" but it may be a completely different issue.

Just saw this thread, and then read the older thread with Brent Weaver's video. I disagree with Brent (and so does Minelab, apparently) and posted a response in the older thread. In any case, once you have a "hole-less" detector, the channel responses can be used to extract a conductivity VDI, as the E1500 apparently does (I don't have one so I'm speculating). But this does not necessarily give ferrous discrimination as ferrous eddy responses can mimic nonferrous eddy responses. Steel bottle caps, ferinstance. But I'm keen to learn more about what the E1500 can do.

This was linked from another recent thread, and I don't recall reading it before. So another better-late-than-never reply.

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From Brent Weaver:
"but if they are a single pulse detector, they are going to have a hole in their detection, period."

This is not necessarily true. The SDC2300 is a single pulse detector and it has no target hole.

The reason for a target hole is that eddy responses have an exponential curve and viscous ground responses have a power law curve. A "single channel" GB detector takes 2 samples of the response curve, and 2 samples (basically a straight line) are not enough to distinguish the two types of curves. Therefore, there will always be a 2-point eddy response that matches the 2-point ground response, and this gives you a target hole.

The target hole can be moved around in a number of ways. Changing the TX pulse width will do it, but so will changing the sample timing or even the bandwidth response of the preamp. So, as Brent says, you can create a detector that transmits 2 different pulse widths, with their own RX channels, and they will have target holes at different places so that, when combined, there is no overall target hole.

But you can do the exact same thing with a single pulse detector, by creating 2 RX channels that place the target holes in different places. Again, this can be done by using different preamps, or by simply creating 2 channels with different sample timings. Normally, each channel takes 2 samples but they can be combined. Above I said that 2 samples are not enough to distinguish the two types of curves... but 3 samples are. You can create a first channel that takes Sample1 and Sample2 and this will give you a target hole, call it Hole1. Then you take Sample1 and Sample3 and this gives you a different target hole, call it Hole2. Combine the 2 results and there is no hole.

You can actually hear this result in the SDC as it gives a wee-woo response for very low conductors (below Hole1), a woo-wee response for medium conductors (between Hole1 & Hole2), and a wee-woo response again for very high conductors (above Hole2). All with a single TX pulse width.

Offhand, I can't think of a PI design that will be damaged by turning it on without a coil connected. In fact, it would be engineering malpractice to release such a design. In designing and building PI circuits, I hot-swap the coil all the time and don't think twice about it. That said, I suggest following the manufacturer's recommendation.

I just checked out the new forum. There are 6 threads, and 3 of them are spammers. If you're gonna run a forum, you gotta stay on top of it. Not only being vigilant with spammers, but also by stimulating conversations and keeping the personal sniping under control. I enjoyed Dankowski's forum in the past but it's really lost the plot and everyone seems to have left. I doubt a new forum script will fix that.

@Aureous is correct. At White's the coil housings and skid plates were made with an ABS/polycarbonate blend, don't recall the ratio but maybe 50/50. ABS alone wears quickly, PC alone wears well but is brittle.

Can you post photos of the control panels? MW might be "modulated waveform," makes a different sound in the receiver.

Pot value is correct, I suspect the wires are crossed. The rear lug (where the gray wire is attached) is the wiper pin and should go to pin 2 on the PCB. Most likely he assumed the middle lug is the wiper pin.

Here is the circuitry around the speaker & headphone jack (TW6):

TW5 is fairly old. Since the headphones work then the audio circuitry is working. Most likely culprits are (1) a bad speaker or (2) headphone jack contacts are dirty.

The best place is next to the current GB pot. Personally, I would move the Gain pot over to the right side where the White's logo is and place the Coarse GB pot where the Gain pot was. Then make the current GB pot the Fine control. The reason is that it's preferable to have the GB on/off switch on the Fine control so the Coarse control stays in place, makes switching between AM & GB a bit easier. Even better than that is to break out the GB on/off to a separate toggle switch. If you never find yourself switching between AM & GB then none of this matters.

For the pot you want a 10k linear taper with a 1/4" (6mm) shaft. They are everywhere. Here is a place to get them cheap but shipping will probably un-cheap them:

https://www.futurlec.com/PotRot.shtml

Which one you get depends on what knob you want to put on it. If you have free Prime shipping then Amazon has them reasonably priced, though you'll have to buy several. Plus side, some options include wires & knobs.

Finally, if you are passing through Republic, WA I'll give it to you for free.

10 hours ago, Cascade Steven said:

I have been rereading this thread and have a question about the coarse and fine adjustment system.  In regards to the TDI SL, in place of using a vernier to adjust the ground balance, is it technically and mechanically feasible to add a 10K pot in series as the TDI Pro uses?  Just curious.  Thanks.

Yes, same thing will work. Try to wire it with coax if you can, for noise reasons. A chopped-up S-video cable works nicely. If not, twist the wires.

3 hours ago, Digalicious said:

That "true" part is interesting Carl. If I would hazard a guess, I would guess that you may be suggesting that even the SF modes of SMF detectors aren't true SF.

Yes, that's what I meant. A "true" SF detector has a narrowband TX (namely, a sinusoid) and a narrowband RX. The SF modes on SMF detectors continue with a wideband TX (namely, a square wave) and a wideband RX. In fact, because the SF mode on an SMF is a square wave, you could demodulate its 3rd harmonic and do salt cancellation, making what seems to be an SF mode hunt in salt like an SMF. This is exactly what the X-Terra Pro does (which is "SF" only), as did all the old CZs.

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In all the EMI I've encountered, a slight frequency shift when using SF on my SMF detector, does nothing. For example, there is little change in the EMI noise when switching between 5 khz and 10 khz, or 10 khz and 15khz. More specifically, in my high EMI sites, 5, 10, and 15 khz is a huge frequency spread, yet the EMI noise is similar in that frequency spread. It isn't until around 20 khz that I get a notable drop in EMI noise, with it being totally gone at 40 khz.

5k to 10k or 10k to 15k are not slight changes, they are pretty major. Most EMI gets "aliased" into the baseband and both 5kHz and 10kHz ends up aliasing 60Hz to the same 20Hz offset. As you go up in frequency (20k, 40k) the alias frequency is still 20Hz but there is also a natural reduction in amplitude (something called the "sinc rolloff") so that is what's helping.

A slight change is 10k to 10.05k, and 10.05kHz aliases 60Hz to 30Hz, which is just a little farther out in the baseband filter and may help. This is why noise channel offsets are very small, you are only wanting to move the aliased frequency in small amounts.

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For EMI noise reduction to work effectively, either the source or the receiver has to be narrowband. I've never seen it work effectively when both the source EMI is broadband, and the receiver is broadband (SMF).

I would almost label that a "fact."

Powerline EMI is narrow-band and is usually the easiest to deal with. However, the powerline frequency varies a little bit over time so you might tune out powerline EMI, only to find it comes back an hour later.

Wideband EMI is much harder to deal with. Electric fences and dog "invisible fences" are really bad, as they usually use a brief impulse of energy, not unlike a PI detector.

Then there is the detector itself. A multi-freq design has a wideband front-end which lets in everything, and makes getting rid of it difficult. A (true) single freq design has a narrowband front-end which does a good job of minimizing wideband EMI, so getting rid of it is not as difficult.

2 hours ago, Chase Goldman said:

No one has been able to actually satisfactorily explain to me what shift/noise cancel/EMI cancel channel adjustments actually do in terms of how they affect the entire transmitted FMF/Multi-IQ/SMF spectrum of any SMF detector (D2/Nox/M-Core/Legend).

The TX frequencies are proportionately adjusted by some small amount. For example, Park mode on the Equinox nominally runs at 2.6/7.8/39 kHz which is a ratio of 1:3:15. Let's say that the next channel up from that is a 2% shift; the frequencies will now be 2.652/7.956/39.78 kHz, which is still a ratio of 1:3:15. That's what I mean by "proportionately adjusted," the ratios never change. The total adjustment range is usually small, no more than maybe +/-10%, which isn't enough to cause any major difference in performance.

Here is a scope probe of the mid-channel waveform (bottom) and the highest channel waveform (top) for the Eq800. You can see that they "look" identical except that the high channel is slightly compressed, by 2.5%. It's like an accordion bellows.

I have no idea what the D2 does in its frequency limit feature, I don't have one to test.

Rick is correct, and there is an explanation. If you are in mineralized ground then it is important to have a correct GB to minimize ground noise. If the ground is not mineralized, then you won't hear ground noise no matter the GB setting. In this case, if you set the GB negative there are some designs that will produce a slight increase in target sensitivity. These are designs that create a "G channel" by adding a slight amount of X channel to the R channel; G = R + kX and we select k so that G = 0 for perfect GB. G then becomes our target indicator, since anything other than G=0 means we have a target.

But if there is no mineralization, then by increasing the factor k we are adding some X target signal to the R target signal. This gives a stronger overall target signal, and it benefits high conductors more than low conductors. If there is a slight amount of ground mineralization, then this setting will make it respond negatively as you lower the coil to the ground. However, even with some nulling effect from slight mineralization you might find that this tweak still gives more depth.

Some people run the GB slightly positive on the theory that it avoids the nulling effect you get with a slightly negative GB. However, either a slightly positive or a slightly negative GB produces the same nulling effect, the former as the coil nears the ground and the latter as the coil recedes. Since ground is not always even, and coil sweeps aren't either, I've always considered a tight GB setting to be preferable, unless the ground is weak enough that the whole explanation above prevails.

Sorry, this is one of those things that really needs pictures.

Todd Marshall at Centerville West probably has new decals. I know the Service Dept had them when I was at White's, and Todd took everything with him.

On 12/9/2023 at 3:40 AM, Guinea1 said:

What I would like to see is modular metal detector created by a manufacturer like Nokta, where you can buy plugin upgrades which change the machine into a higher preforming detector without having to purchase a completely new unit.  Something similar to the old modular Treasure Baron units designed by George Payne.

That would transform the slim, lightweight Legend into a big, bulky detector. Besides, the Legend (and all the other newer models) are 100% DSP so there is no hardware to upgrade. And the firmware is upgradeable, so you could argue that the Legend already supports plug-in upgrades.

The original concept for the White's V3 was to start it out as a more basic detector (far fewer options) and sell progressive upgrades at, say $99. The upgrades would already be programmed in, so for $99 you get a passcode that unlocks the next level of features. The brass didn't like that, so it was released with everything. However, in the VX3 model this concept was sneaked in, though it was never implemented. So a VX3 could be upgraded to a V3i, if the computer that generated the passcodes hadn't been trashed. I think this model of upgradeability is a bit harder to swallow, in that you've already bought the detector with all the features, you just can't use them until you pay extra. I know the auto industry is doing this, and I don't care for it a bit.

Many years ago, in the last-gasp dying days of film cameras, I owned a Minolta 7000i. It had plug-in modules (about the size of a normal SD card) that could add modes and features to the camera. That would be the most likely path for a "modular metal detector" these days. But with the Legend, what would you add that's not already there? And would you pay extra for that?

Yes, it covers the basics reasonably well.

On 11/30/2023 at 9:19 PM, machinesmith said:

Jim is 100% correct. Fow whatever reason (my guess the calibration with the analog timers, would have been the reason they moved to a microcontroller in the SL).

Except for the first 200 units, the TDI also used a micro. A micro is simpler and cheaper. I wrote the code for both and recently reconstructed the code to do some experimental work.

Compass77bAT.pdf

I don't know if Don is still making shells, but he's the only one I know of to try.

Get some microballoons to mix in the epoxy, it will make it much lighter. I bought a bag somewhere, maybe AliExpress.

Try Don Bowers (dfbowers) via the Geotech forums. If you epoxy-pour the coil you really don't need a bottom.

Might be the battery contacts. The C-cell pack contacts 2 metal fingers inside the box, if those metal fingers get bent backwards the battery pack will no longer touch. Probably need to open the main box and (gently) bend the fingers closer to the battery compartment.

Might also be the keypad flex connector. You can open the display pod, find the flex connector, and wiggle it in the receptacle. Often that will freshen up the contact. The keypads eventually wear out, I know that years ago White's ran out of spares. They talked about getting another batch made but don't recall if they did.