Geotech

That's what I'm thinking.

Just got back from Florida. I took 4 detectors, packed them in a big plastic tote with straps to hold the lid on, and checked it. Their only concern was whether there were any loose batteries. Had no problems.

Not much of a leap, Minelab did this 34 years ago. It was called the "Sovereign." Then it was called the Explorer, and then the ETrac, and then the CTX3030. All of these were VLF multifrequency with time domain signal processing. But I suspect the GM2k is something a bit different.

No, either will work. You can also fake an active locator by disconnecting the wire from power and hooking up a signal generator to the wire. Set the sig gen to the same frequency as the detector and you should get a strong interference.

The free 811 locating service is only for public utilities. Once you get to a home's power meter, everything on the other side is private and you have to hire someone. I've used a Fisher Gemini 3 to trace the buried power line out to my well house. For that, you disconnect the wire from power and connect the Gemini TX box to the wire. This is "active tracing." You can also do "passive tracing" by detecting the 60Hz power signal from the live wire. For this, you want to do it when the pump is running and drawing current. There are specific locators for doing this, but you might be able to do it with an ordinary metal detector that has a frequency offset feature. In this case, adjust the offset until you get maximum interference and use the biggest coil you have. Finally, there are rental places that often have line tracers like the Fisher TW-6 (same as the Gemini) or passive/active tracers like a Rigid or Radio Detection unit.

Keith is out of the picture. Health problems, and many unreturned detectors.

Putting metal in the coil of a prospecting PI is a big no-no. As you sweep over variable ground and hot rocks, they alter the magnetic field which then lights up the "static" metal in the coil and makes it sound like a transient target. Even solder joints can be a problem. Also, even the most efficient energy-recycling PI design needs around 25W-hrs of battery energy for a decent hunt time and that equates to another quarter pound of weight you would need to swing. I know that XP is working on a PI design and if they go the wireless route I would imagine that the batteries and circuitry will be in the lower rod, away from the coil. Personally, I don't see much advantage in that as you still end up swinging more weight, albeit with a lower moment of inertia. But not as low as putting it under the arm cup. Then again, I'm not a big fan of the Deus/D2 design; I'd rather have the coil cable, a lighter coil, and fewer things to charge.

Your pic shows an early TM808 with Cave mode. This was made for White's by Discovery Electronics, originally designed by Jim Karbowski. The VLF-GB mode runs at 12.5kHz and the Cave mode (TR) runs up around 80kHz. What else do you want to know?

Fisher is a straight VLF-GB, no disc. 4.5kHz. Should do OK on silver, probably sucks on small gold. The BH3 is a BFO, probably sucks on everything. Nice pics, tho.

Oh, I read it wrong. I thought you were saying the F75 is no longer available. Never mind [in Emily Litella's voice].

The motion filters are high-pass filters that remove the slowly changing ground signal. This leaves you with a supposedly ground-free target signal, which should improve target ID. But the motion filters (or the subsequent DSP) can combine co-mingled target responses in a way that causes masking. Whenever I hear a motion-mode response that is not clean (has an audio truncation, glitch, or other artifact) I switch to static AM mode and usually find there is a second target.

I don't have one that I can open. Let me look around and see if I can find any old prototype pieces.

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That's true. Mineralization compresses the TX field so it doesn't go as deep.

That's the downside to moist conductive soil -- it then becomes a signal and can be noisy. In most places (parks and such) it isn't strong enough to be a problem. At the beach it's very strong and you deal with it using MF or longer sample delays. In the desert it's usually not bad unless it's just rained or when running a really big coil. I've done that at Rye Patch and could hear the saline response even though it hadn't rained in a while.