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Steve Herschbach
12-16-2011, 02:59 PM
Detector companies bug me. I can spec out a perfect detector I know I would buy so I know others would buy, and I know the technology exists. My perfect VLF gold machine would be similar to the White's DFX. Dual frequency with the ability to run both at once or either only. Usually that means a harmonic like 15 kHz and 60 kHz but I am going to get greedy and ask for 15 kHz and 90 kHz. Run both together or either one separately. The unit should also have a DFX like ability to notch out not only any target types but also multiple ground types. I want to be able to notch out the ground and also notch out a certain hot rock. In other words, more than one ground balance setting.

Who is going to do it first so I can buy it? And sell a bunch also. Sorry Steve, we don't ask our users what they want. We just make stuff and tell people they want it. Why listen to people who have bought by themselves more detectors than a small town and who will continue to buy them until they die?

The most impressive dealer meeting I ever attended was a Honda Power Equipment meeting. It was full of engineers asking "what do you want? What do your customers want?" Why is it so few companies get that? I know what I want, I know what my customers want, and nobody will make it for me. What is up with that? Do not tell me it will cost too much for people to buy. I have over $10,000 invested in detecting gear. I will pay a premium for a premium niche detector and so will others.

Hello, over here, I am your customer, I want to give you my money. Hello! Hello!! Anybody home? Hello!

Steve Herschbach
Steve's Mining Journal

12-16-2011, 03:28 PM
Good Idea,I'll take one Steve, Bob

12-16-2011, 03:55 PM
Great idea Steve ! All that and in a water-resistant shell. Capitalism works....lets make some detectors for Alaska. Seems like there is a niche.

12-16-2011, 06:11 PM
Dave Johnson would be the senior project engineer

12-16-2011, 06:16 PM
Dave Johnson would be the senior project engineer
not bugs or Doug, eh ?


12-16-2011, 08:40 PM
A long time ago in a far away place, the Army decided because I was an electronics geek and a ham radio operator that I would be a good radio repairman. Only thing that changed was I got too old to be in the Army.

That said, here is a possible way. Square wave transmitter and two receiver front-ends. Transmitter on 15KHz and receivers on 15KHz and 90KHz (6th harmonic). The easiest way too integrate them is with a solid-state diode switch operating at 10-20 hertz or selectable. Same signal processor for both.

Detector manufacturers, no need to send money. Just send me one of these new whiz-bang detectors so I don't have to fight for it.

Old Radio Tech
12-17-2011, 06:52 AM
OTE - the power is in the odd harmonics, and by the time you get to the 6th your signal would be very weak. But you could take the sixth (sharing everything before that) and run it through a separate driver and PA. But now that I think on it, I don't think you would want to use harmonics, it would cause serious intermodulation. You would need to offset your frequencies enough (maybe 17KHZ, 54KHZ, 85KHZ??) so you could have them transmitting at the same time. So Steve, that may be why they don't make a machine that allows both to be on at the same time, the two signals would interfere with each other too much. I'm not sure whether the separation between 15KHZ and 90KHZ is enough to preclude interference even if you offset them some so they weren't exact harmonics. Also, having two antennas that close together in the coil, the power from each transmitter may desensitize the receiver of the other if both were transmitting at the same time.

12-17-2011, 09:00 AM
Steve what are you trying to do, start a new gold rush? Ha ha If the detectors got any better there will be no gold left for my kids to look for! Well, that is if in the future kids actually go outside... You do have a great point, but geez the winter aint even half over yet and you're having this discussion!!! Just giving you crap..... It does seem to me just like our cars and trucks, they dont get bewttewr mileage till we make them do so... If you keep the rant up, they may listen! I kinda hope not just yet, as i'm gettin kinda fond of my gpx now. please dont delete me.

Steve Herschbach
12-17-2011, 09:32 AM
Multi freq tech already exists.

The Fisher CZ units have been around forever and process at 5 kHz and 15 kHz. It does not take more than one transmit and one receive coil. http://www.fisherlab.com/hobby/fisher-cz3d-metal-detector.htm

The DFX runs at 3 kHz or 15kHZ or both. http://whiteselectronics.com/info/field-reports/51.html The V3i runs at 2.5 or 7.5 or 21 kHz, pick any one or all three at once. So far only White's let's you do this. Minelab has detectors that are locked into being units that let you select a frequency or which process multiple frequencies but not both in one unit.

12-17-2011, 10:30 AM
Old Radio Tech
The receiver desensing issue was why I suggested the diode switching at 10-20 Hz. If the receiver is trying to receive both the fundamental and 6th harmonic at the same time you are right about the IMD and desensing issue.

Again, you are correct about the need for a separate drive and PA. So now we have two drivers and PA's rather than one. The driver for the 6th harmonic will probably need 2 stages to make up for the low harmonic output on the 6th. No biggy.

I agree that there might be a need to have two concentric receive antenna coils. Again do-able with one caveat. The unused receive coil must be open circuited while the other one is active. Again a diode switch. The problem I see with attempting to use one receive coil boils down to the large difference in frequencies and the need to switch out a large tank capacitor for a vastly smaller value. In radio design, the most effective method is swapping out the tank coil. A work-around would be several caps in parallel and switch out the high value caps to get resonance on the 6th harmonic. Sounds kinda kludged up to me. A potential problem with switching out the caps is the change in the loaded Q of the coil with the frequency excursion.

Nowadays with digital signal generation by MPUs and PLL circuitry, the whole frequency change issue is moot as long as the rate is slow enough for getting a lock.

I think Steve summed it up. Especially when I tend to have the same problem designing and building ham radio gear. The designer falls in love with their ideas and the buyers get dragged along. The proverbial, "This is what there is, take it or leave it."

Please don't get the idea I can design a detector. 1. It is outside my area of expertise. I build CW and SSB radios. 2. I still have problems programing EEPROMs and PICs. Let alone attempting a MPU.

I understand electronic theory circa early 90's. I understand the principles of detectors, but I am just a hobbyist anymore.

As an aside. Steve I noticed you choice of 90KHz. The spelunkers (cave explorers) in GB have chosen 87KHz as one of their frequencies for cave communications. Mayhaps they had a good reason besides frequency availability from the regulating authority. Or maybe it is just that attempting to build a lower frequency induction-type antenna was impractical. The lower the frequency, the bigger the antenna (wire length and diameter of coil) to achieve some measure of efficiency. The smaller the coil for a given frequency, the greater the number of turns to get resonance.

Interesting thread. Thanks for letting me in.

PS I suggested the switching at 10-20 Hz as about the fastest practical and not be noticeable to the operator. Too slow and the act of sweeping the detector while it switches frequency would result in a target only being hit by one frequency rather than the desired two. Too fast presents it's own problems electronically.
Eric NL7ZW

Old Radio Tech
12-17-2011, 10:41 AM
Steve, Thanks for the input and links. I can see how a detector could transmit on multiple frequencies using one antenna if they were multiples (3,6,9,12,15), harmonics. My guess is the signals aren't transmitted simultaneously, but toggled, each frequency for a short duration, then on to the next. If they do transmit multiple harmonics simultaneously, then the power of the signal goes way down as you go up in harmonics. I need to learn more. I sent Whites an email asking where I might find theory and technical information. Is there anyone local who repairs detectors? If not, do you think there would be a market for repair locally? I could really get into this.
If I might ask, how reliable is everyone finding their detectors to be. Mean time between repairs, need for periodic calibration and alignment, average repair costs, etc.

Old Radio Tech
12-17-2011, 11:00 AM
OTE - understood. It sounds like the manufacturers are trying to make a unit that does too much. Anytime you design and build a comprimise, you sacrifice in other ways, power, sensitivity, frequency selectivity. On another note, are the coils designed to transmit straight down, or is signal radiating out the sides? Does the signal have a focal point, X" below the center of the coil, based on the size of the coil and the frequency. If so, you might be able to have components in the coil that are electronically switched in to change the focal length, and then the detector could scan from 0" down to x" making it much more sensitive to smaller, deeper targets

Steve Herschbach
12-17-2011, 12:00 PM
Bad news Radio Tech - detectors are so reliable it is scary. I think maybe one in 500 has to go back for warranty issues. They basically last forever and and in most cases never need to be recalibrated or tuned.

You are absolutely correct that a single frequency packs more punch than multiples. And when you study up remember part of the frequency thing is hype. It does not matter so much whar is transmitted as it does what is received and processed. Minelab advertises units at 28 frequencies but I believe only three at any time get used. I do not want to stick my neck out too far on that though. I am not a tech wizard. I care more about what they do than how they do it. Anyway, that is why I need the option to select single frequencies. Normally only one will be used. But running in multi mode would be useful for odd places like salt flats.

Reno Chris
12-17-2011, 01:12 PM
Steve - I know what you mean. You mention the DFX, but the problem there is gain. I think the Eureka is also underpowered when it comes to sufficient gain to properly do the job. Of course it’s not that simple as jacking up the gain causes some other very real problems.

We need a user selectable, digital, multi-frequency machine, with the gain sufficient to find very tiny gold like the GBII. The problem is that doing a digital GBII isn’t going to be easy. We’ve talked about that – in my interview with him Dave admitted it would be “difficult”. I got the drift that he was more optimistic about multi frequency machines. I just don’t want a multi-frequency machine that runs at medium and lower - 18 and 4 kHz. Without the upper frequency stuff like the GBII or the Goldmasters, it’s not what I am looking for.

I honestly think we could all come to a pretty close agreement on what we’d be looking for in a top flight VLF detector that was within the reaches of current technologies. The problem is that the makers produce what they think will sell well, not cost too much to make and is not too difficult to design. You are right that none of them listen too closely to what their customers want to buy. Perhaps we need to speak louder and let our requests be known to all of them?

Here is what I think is a reasonable list of features, all of which are found in one form or another on VLF machines currently on the market, just no one machine with all of them. Why can’t they be combined? I’d be interested in comments on what realistic additions would be necessary to make a top of the line, cutting edge VLF for prospecting?
Multi-frequency with user selectable High (60 to 90 kHz) and medium frequency (15 to 20 kHz).
Dual frequency operation option.
Gain sufficient to find very small gold in the high frequency setting (must at least equal the GBII).
Ability to discriminate out hot rocks.
Ability to handle fairly highly mineralized ground – even if only in a special discrimination mode.
Ability to notch out not only any target types but also multiple ground types, so the operator can notch out the ground and also notch out a certain hot rocks. In other words, more than one ground balance setting.
Memory to save notch and discrimination settings for various locations.
Digital design with a controlled volume output, maximum signal loudness limitations, threshold loudness control, variable audio tone, adjustable gain.
Both manual and automatic ground balance adjustments.
Tracking mode option.
Digital display of GB, GB settings and target response.
Selection of different sizes of coils in both concentric and DD configurations.
EMI noise reduction adjustments.

The other thing is that everyone is now making the same thing - mid range htz, "do it all" machines powerful enough to do a decent job on gold but with a sufficient discrimination to use for jewelry and coin shooting. The problem is that “do it all” machines by nature must make compromises. We have the MXT, Tesoro Lobo, T2, GB Pro, F75, AT Gold, XTerra 705, etc. - it’s too much of the same thing over and over slightly re-done and re-packaged. Yes, each model has its own subtle differences, but they are all in the same design class. The manufacturers have figured out these are popular detectors (and my guess is that they are not that difficult for a good EE to design), but how many similar ones do we need? Half ton pick-ups have long been the best selling vehicle in America, but what if the only car any of the manufacturers made was a half-ton pick up, it would be a pretty sorry situation.

We’ve all heard the saying “Build a better mousetrap wand the world will beat a path to your door” – We just seem to be stuck in “build a mousetrap like everyone else and you can keep your head above water.”

Steve, you have a great holidays, say hello to the family and get some sleep my friend. 4 am is a little late (early?) to be up posting on forums.

Steve Herschbach
12-17-2011, 01:38 PM
Perhaps we need to speak louder and let our requests be known to all of them?

Precisely why I decided to post on several forums to see what response I could stir up. They read the forums. Maybe someone with some authority will see it and tell their troops "just do it".

Good post Chris. Merry Christmas to you and your family.

Old Radio Tech
12-17-2011, 03:07 PM
Would this feature be advantageous? A coil that you could electronically change it's size, coupled with multiple frequencies and gain levels - programmable. With a trigger or button on the handle you could make a pass in small coil, low gain, low frequency, pull the trigger and next pass would be larger coil, higher gain, and higher frequency, and then another coil/gain/frequency combo, or any combination you wanted to program. This would allow you to maintain your sensitivity rather than compromise in a multimode. It would mean more passes over the same spot, but I think its within current technology. OK, time to be quiet and learn now.

Reno Chris
12-17-2011, 11:00 PM
Would this feature be advantageous? A coil that you could electronically change it's size, coupled with multiple frequencies and gain levels - programmable.

To be electronically changeable in size, you'd need to have extra coils of wire in the coil assembly. One of the things you really dont want in a coil assembly is extra metal. When you amplify the signal from a coil to ridiculous levels so you can see small gold, that extra metal makes for problems. Not to mention it makes the whole coil assembly a lot heavier.
You actually want higher frequency on smaller coils - the higher frequency is to see smaller targets not deeper ones. As a general rule, the larger the coil, the more ground mineralization it will see and the higher the frequency the more the ground mineralization problems you have.

Throughout it all you want as high a gain as is practical given the detecting environment.

Old Radio Tech
12-18-2011, 06:02 AM
Thanks Chris - I think it could be done without adding extra coils of wire. Using solid state devices placed at certain places in the coil assembly these devices could change the apparent overall length of the coil, making it electrically a different size. Besides the solid state components there would need to be a few extra wires in the control cable, but they could be small gauge and wouldn't add very much weight. So I guess the bottom line would be would it be advantageous to be able to change your coil size on the fly, cause you can already change the frequency and gain.

Steve Herschbach
12-18-2011, 08:38 AM
Almost any feature you can imagine can be useful in metal detecting if implemented well. The problem usually is trade offs are required.

12-23-2011, 07:38 PM
So if you can hear sound over fiber optics,why cant you send a signal the same way? no wires involved. Just something to think about. I realy D.N.S. I just like to find

Old Radio Tech
12-24-2011, 05:53 AM
even though the frequencies used are mostly in the audible and ultrasonic ranges, they aren't audio signals. It's a magnetic field thats being varied at an audio rate in the coil.