why

[Skippy]

You're correct, it IS complicated. Things that make it like this include:
*The ground gives a signal, and the size of this differs with frequency, increasing with f. So a higher f will in principle not help you get depth.
*Different discrimination circuitry give different results - analogue vs DSP microcontroller, simple vs complex
*Search-coil size matters. Big coils don't find tiny targets so well, even though in general they seem deeper. The tiniest specks I've found have all been with the 5 inch DD coil, eg. shotgun lead shot 2mm diameter
*Probably coil shape, too, DD vs concentric, round vs elliptic.
*Then factor in target size, vs. metal type. You will find that targets with 'corner freqs' of 1 - 3 KHz are all quite large, eg U.K 2pences, US Quarters, so they are easy to find by virtue of being large, so a detector that runs at 10 -15K can still find them deep. But it will also find smaller targets, becausethe frequency match to the target improves.
+many other things.

[Koala]

Skippy or another; what Freq. would you think a Golden stater or one size bigger gold coin is best?
Ive been testing a little with a 8 gram Gold coin size 22-24 mm with those different detectors I got, and to me it seems that 8-12khz did it best, but there wasn't much different in depht with 8/12khz, 17/18 khz or 25 khz.. I think the round form helped the lower freq.
The reason I tested this and used some time to find out which Detector I got there would do it best, is that I got a field were 3 gold coins (6 gram) was found some years ago.. This field is just been sown and are ready to search, flat like a pancake.
One week of rain and the soil is allso friendly this way.(damp I think you call it).
Only sad thing is that this field is a club field, so I'm not the only one trying, and that has been going on since last coin was found in 2011. The good thing is that I live near, only 5 km to this field.
Henrik.

Don't know how scientific the testing was but this link answers your question.

[Henrikras]

Thanks Koala. That was a George Payne artikel.

[muddy fingers]

Yes, all the variables as outlined by Skippy do make the frequency subject very complicated. I think speed of swing is yet another important variable as well. I suppose it must be linked to the "recovery speed" of the detector, but I've noticed if I swing faster over a signal it often disappears, whereas an ultra slow swing can make the signal much easier to hear (distinguish?) from all the general background effects. I've found so much more in the way of tiny coinage like cut quarters since using the Goldmax Power (18 Khz) and did get a gold stater with it though that was very near the surface. As I said before, I loved my old Toltec 100 (concentric coil) for its ease of use and fantastic I.D capabilities (targets very widely separated on the meter, and Disc and All Metal modes detected to the same depth) but I have often read, and I would like your opinions on this, that many of the old generation detectors such as mine, lacked "power." What exactly is meant by this and what is it chiefly due to? The Toltec ran on 12 volts.

[Skippy]

This thread on a UK forum caught my eye: a cut half of a typical medieval penny (18mm diameter, about 0.6 grams) at 10 inches with a CTX. Found on pasture, with few targets, so there is the opportunity to investigate every target for a hint of non-ferrous (plus being prepared to risk digging iron). So it's not just the high-freq machines that can do it.
http://www.metaldetectingforum.co.uk...?f=120&t=64824
I don't have any hammered coins in my 'test garden', but I wouldn't consider burying a cut half at 10 inches, it just sound too hard.

I do keep wondering if there is a market for a high-frequency dual-frequency VLF machine. The sort of thing I had in mind was a 13KHz / 39KHz machine, or thereabouts. It's well known that Fisher are working on a new dual-freq machine, but most people seem to think it will be a "New CZ", that is a 5K / 15K unit (like the CZ5, CZ70 etc) but in a modern package, eg. the GoldBugPro / G2, or F75 / T2 style. If it weren't so darned difficult and expensive, it would be a great project to hack a CZ machine to 15K / 45K or similar.

[Henrikras]

I would like to see that 10" dig on a video... .
Skippy you can make your own cut coin, it dosn't have to Be an old rare one.

Dual Freq. wouldn't that slower down the recovery !!! Unless you got a twin Detector built together at one ?

It could be funny some day to built a dobble PCB Deus board in one box... And use two control unit with each of those two receiver boards from inside two coil, connected to only one coil. Then I got a Very fast Detector going in 17 khz and 8 khz at the same time.(or other different settings)
Thats stereo detecting, 8 khz in the right ear and 17 khz in the left ear.
None had ever tryed that. Prize !!! Ups.

Henrik.

[Skippy]

There's no real problem getting a cut half off eBay, they can be obtained for very little money, I have my own, but for sentimental reasons I won't re-bury them. I use a fake cut-quarter farthing for airtesting (and pinpointer experiments), it's a 7.5mm x 7.5mm square cut from the centre region of an aluminium drinks can. It works quite well.
I don't see why a dual-freq machine has to be slow. The problem is: if you hacked a Fisher CZ, you would have the slow response of that machine. Better to hack an F75 / T2, except you're constrained, because half the 'circuitry' is inside a DSP microcontroller, including the ground balance. So that puts alimit on what you could achieve.

[Koala]

Henrik beat me to question 10" on a cut half. More likely something else going on either some else in the same hole that the detector latched on to or it fell out of the side wall. From YouTube vids I have seen the CTX 3030 preforms about the same as a T2 and would be running out of legs on a full let alone cut before 10". I have dug a good signal before now that have been two hot rocks together each on there own give no signal so one in a hole with a coin would boost the signal.

[Skippy]

That's always the trouble with things like impressive but plausible depth claims. You can be cynical, and say that having spent 2K on a detector, he's going to let everyone know how good it is. But we weren't there, so we like to be skeptical, and say that it fell down / wasn't actually that deep / something else in the hole. And of course none of us have detected on that particular bit of pasture, so we don't know if it's mild low-iron low-mineral soil. It's quite possible that other top-end machines would give an iron tone on it, but if targets were really scarce, you might reason it's deep, so could be anything, and you dig it...

[Henrikras]

We never know .. I found a deep small low conducted hammerd Once. Got a nice signal -but that was from the bottom in same hole. Since that day I Allways go over the hole and the soil again before I cover it up and move on. But that properly one out a thousand, so in 5-10 years from that day, it will Maybee happen again.

[golfnut]

on this vid at 7:50sec this etrac pulls a 10" hammered fairly easy. I know nothing Ive made would get that. Must try harder

http://www.youtube.com/watch?v=EkcFWajzRzA

[Koala]

We never know .. I found a deep small low conducted hammerd Once. Got a nice signal -but that was from the bottom in same hole. Since that day I Allways go over the hole and the soil again before I cover it up and move on. But that properly one out a thousand, so in 5-10 years from that day, it will Maybee happen again.

Always do



Have notice that if you have a week signal and you don't get it first go then the signal is stronger when you re scan the hole. Is this due purely due to less ground absorbing affect or is there something else going on here. Sometimes you can do the same just by scrapping you foot over the ground moving a few millimeters of earth changes a iffy signal to a good signal even if you raise the coil to the original height.


Kinda getting of topic. Would like to test a range of detectors in the field and swing each over real target before it is dug. Even that not cut and dried as the coils would be different sizes.

Maybe we should aim for the best all round coil before attempting the perfect detector.

[muddy fingers]

There are always so many claims and counter claims regarding the capabilities of various detectors on these you tube videos. The open minded observer is left wondering what to think. Also, some detectors perform well on "clean" unmineralised ground whereas on iron and hot rock infested ground they maybe subject to a lot of masking effect or slow recovery speed. I always tend to think its best to have a small range of different detectors and use each one on the type of ground to which it is most suited.

[hoadlies]

MORE POWER????????????????????

HI TO ALL ,, I am not as experienced as you fellows on Metal detecting depths etc..

But I wonder if the designers of commercial detectors are overly-concerned about battery hours of use????..as today we have a plethora of battery options ,Rechargables ,lithium cordless drill packs, Gel-cell ,etc etc ..

If power is a consideration as to obtain depth etc It would be nice to supercharge some DIY builds ?????..

I have done very little field work on M/ding as I have only started this hobby recently I however with much help from this site & its many experienced guys I have built a IDX-PRO & made a few coils etc ..
My IDX works very well with a DD coil dimentions as described in the TGSL page ,but with the IDX specs & a Colinier By DONS design ,I had a chance to test it against a ''FISHER-F70'' the other day & the fisher is way stronger [depth-wise] & is very light weight with its 11'' coil & very good GEB ..

I am pleased with my IDX as its DIY built etc & cost was quite cheap ..

AS said above I would not be concerned about carrying a remote battery pack if more current use would get better results..
ANY-IDEA's ?????????

CHEERS FROM OZ,,,,,,,,,,,,,,,,,,,,BARRY..

[Skippy]

Quote:"I wonder if the designers of detectors are overly-concerned about battery hours of use????..as today we have a plethora of battery options ,Rechargables ,lithium ,etc"
This is rather self-contradicting - now is the time when power-hungry electronics are much more viable, due to the better batteries.
Sadly, detection depth is not really "power sensitive", it's simply a case of finding very small target signals in the presence of a reasonably significant ground signal. "more power" just increases the ground signal, and the target signal, by the same amount, gaining you nothing. There are some gains that result from more TX power: electrical interference (radio freq, electric animal fences etc) becomes less of a problem, and circuit noise on the RX side (resistor noise, semiconductor noise) is not so important.
But to take the F70 as an example, about 10 milliwatts (might be less) of battery power ends up in the coil, mostly warming it up. The rest of the electronics takes an impressively low 250mW (hence the 30+ hours on 4 x AA cells).