Detector Design

[Canewrap]

How are the main detector companies designing their machines? Seems to me that the business end is really at the coil and if the coil isn't suited for the task, it doesn't matter what processor is connected to it. I realized this in comparing setups on a few of my detectors and masking is almost total with some coils and still tough with others. Would be neat if someone developed a new detector by 1) considering the best set of coils for a variety of conditions, toughest to easiest (trashy mineralized ground to easy separation and low mineralization) , 2) ergonomic design (best balance vs. weight, while taking design ruggedness into account. The lightest detector is not always necessary if its balanced right (converting my Musketeer to a straight shaft with moveable box position showed me the value of that)3) Simple interface (if digital) that has buttons that allow launching different screens (or even turning the screen off or into a minimal display), with a screen covering like the one on the MXT (substantial plastic) and not flimsy like Fisher's F-Series. Also, would have to be a combination of analog for the sound and digital for the output (perhaps a digital signal strength bar that can do a fine gradiation and at least 200 VDI) If someone designs this machine I will scrape together the small fortune and invest in it, but I don't see it happening in the hobby market, without an inspired entrepreneur.

 

[gilfordberry]

What I'm waiting for is a company to put a combination pulse induction - vlf machine together. I believe it could be done. The transmit and receive coils would function separately in VLF mode, and be "piggybacked" (looking to the controls like one coil) in the pulse mode. You could hunt in PI mode - don't worry so much about time domain - then switch to the VLF mode after you have found a target to easily identify it. Now, this might be a bit expensive, but the only tricky part would be the coil function switching. I'm also expecting much more efficient coils to be built using semi-superconductor materials. Could be much more powerful and still be very light. I doubt I'll live long enough for that one, though. Gil

 

[UK Brian]

What you have at the moment is pulse machines that can swap the coils to turn them into a VLF or induction balance discriminator. The Deepers version, which I think is called something like the 1/2, has a black coil and a white one. One gives you a standard pulse (no discrimination) and other turns the machine into a full range VLF discriminator.

Grizzly (sold through MD Detectors) have gone one better by providing three coils. A hoard hunter pulse coil that will find large objects at more than few meters. A conventional pulse coil for smaller items that are beyond normal VLF depths and an induction balance type coil for where discrimination is needed.

To get nearer to what you describe there have been several pulse machines that have the pulse as the primary search mode that provides the audio and maximum depth with an induction balance type meter to provide ferrous/non ferrous discrimination. No coil changes needed !

The first of these I'm aware of was the P.P.D.1 designed by Eric Foster and sold by his company Location Technology around 1981. Drawbacks were weight and battery consumption. All P.I.'s ate batteries at this time. Also the discrimination side didn't have the depth of the pulse side so you had to adopt the detecting practise of those using the Arado, Fieldmaster and similar non motion meter discriminators ie no reading on the meter you had to remove some soil until you did get a meter deflection.

Protovale soon came out with a similar design, the Pulse Analyst, but their's had battery miser circuits and ran off a handful of AA cells rather than the stack of U2's of the P.P.D.1. They used the plastic case from the Whites Beachcomber range.

About two years ago I was sent a Polish version of the above two detectors. The original version was poor. Lack of depth, poor pinpointing etc but they revamped it and tackled those problems but didn't get to grips with the fact that the discrimination could not cope well on wet salt or black sand so they went back to the drawing board.

Eric Foster himself told me that he had an improved version of this principle "under the workbench" so perhaps one day this may see the light of day.

Another British company ( Wrights ) produced the Groundhawk ten/fifteen years back. This detected as a pulse and when a target was located had to be switched to a discrimination mode. The principle used was similar to B.F.O. machines ( some of these did have depth and discrimination ! ). I saw the designer of this machine on the beach one day and he had a large coil that he was wearing round his body suspended by straps over his shoulders. He was walking a huge beach covering about a four foot width. Mark the good signals with your foot, swap back to the smaller coil and rewalk the ground covered checking with the stock coil.