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Which Frequency Is Running In Each Mode?


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Steve and the rest of us . . . 

Without any doubt, this site is the 'Top-Drawer'  source of accurate information, in all aspects of metal detecting - technical to use in the field! I'm totally impressed. There are so many knowledgeable detectorist hanging out on this site, who are eager to share information. 

I have an OK engineering background, but I'm short on actual use in the field. 

Thanks to all,

Billy

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25 minutes ago, GB_Amateur said:

Thanks for another one of your classic, excellent long, detailed explanatory posts, Steve!  But I'm left with one confusing thing.  The Fisher Gemini 2-box T/R detector (~90 year old design by the original and founder, Carl Fisher himself, but still being sold today with a bit of modernization 😁) uses 82 kHz operating frequency.  How does that squeeze its way into all of this?

Good question. I think it's just that it is in effect just a huge coil, so huge it is insensitive anything smaller than a baseball, and ground also. It certainly does not act high frequency when it comes to what sets it off, targets and ground alike. It acts low frequency though we know it is not. Just very low gain maybe? We are talking quite literally about the oldest and simplest detector design ever sold commercially. Interesting, but I think more of apples to oranges in a way. Carl would know.

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8 minutes ago, Steve Herschbach said:

Carl would know.

Presumably you're referring to Carl Moreland.  :biggrin:  I only bring up that obvious point because I confused the issue by giving the name of the inventor and company founder as 'Carl Fisher' when his actual first name is/was Gerhard.  Gerhard probably knows the answer, too, but I don't think he's a member of this forum anymore.  :laugh:

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8 minutes ago, GB_Amateur said:

Presumably you're referring to Carl Moreland.  :biggrin:  I only bring up that obvious point because I confused the issue by giving the name of the inventor and company founder as 'Carl Fisher' when his actual first name is/was Gerhard.  Gerhard probably knows the answer, too, but I don't think he's a member of this forum anymore.  :laugh:

I missed that. You said Carl Fisher? No, it's Gerhard. But yes, I mean Carl Moreland (Geotech)

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What you will find is there is no singular answer to the question you are seeking because the variables in play are simply too complex.  I get the impression you are looking for the optimal frequency to detect . . . “

No not that at all. I found the science interesting, and I guess I was looking for a 'meaningful understanding' that made sense to me. I understood what -3db half-power was about in electrical power transfer and impedance matching, so I set out to see if my intuitive feel was accurate as applied metal detectors. It helped me understand why a specific frequency is better for a specific target, as opposed to accepting and putting to memory. Like why a dime reacts better to 2.7kHz than say 15kHz? Other than the manual says so.

I'm kind'a weird in that way. I like understanding as opposed to running on 'blind faith' one may say. As you have mentioned, be careful to not get trapped in the technology thing. And you are right. The bottom line is to get outside and go detecting!

I appreciate your comments. I need those 'checks and balances' to stay focused.  Later, Billy

BTW . . . I would really enjoy traveling to Nevada and detecting with you and others in that area. I've lived in CO's Eagle River Valley (I70) for over a year in 2013-14. I love the Western states. I'm hard to pinpoint at times, as I enjoy outdoor adventures and yet I'm into technical details, etc. I could learn so much out there! I live in SE Georgia, and raised my family on the Ogeechee River near Statesboro.

I got a few articles to read now. Like I said, this is a great site to be part of.  You and others have done an excellent job with it.

 

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6 hours ago, GrievousAngel said:

Like why a dime reacts better to 2.7kHz than say 15kHz? Other than the manual says so.

The gist of my post is that no, that's not actually necessarily true, despite what the manuals say. If it was all about theory, maybe, but there is simply more to it than raw targets and frequency.

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5 hours ago, GB_Amateur said:

Thanks for another one of your classic, excellent long, detailed explanatory posts, Steve!  But I'm left with one confusing thing.  The Fisher Gemini 2-box T/R detector (~90 year old design by the original and founder, Gerhard Fisher himself, but still being sold today with a bit of modernization 😁) uses 82 kHz operating frequency.  How does that squeeze its way into all of this?

The Gemini (and TW6) is primarily a utility locator although it does get sold to occasional treasure hunters (the TM808 is a better choice for that). The best way to use the Gemini is to split it apart, connect the TX to the line or pipe, and then use the RX box to trace it out. At my previous home I traced the power line out to the well house, about 150 feet.

In utility locating there are 2 popular frequencies used: 8.2kHz and 82kHz. 82kHz is the better choice for tracing metal pipes because it does a better job of jumping across the poorly conductive joints. Probably why the TW6 runs at 82kHz, and the Gemini is just a copy of the TW6. As a unified 2-box detector the Gemini is not especially sensitive. I know that it failed my 24" silver cache test, but so did the TM808 and everything else I tried.

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I have the 2 box Bloodhound coil set for my Garrett CXII. It runs in the Non Motion All Metal mode at 6.4 kHz if I remember correctly. I have a cast iron Dutch oven w/ lid buried at arm's length(about 27") in mild- medium mineralized soil. I can get a soft but noticeable response from it.

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  • 3 months later...
On 1/20/2022 at 2:35 PM, Geotech said:

As a unified 2-box detector the Gemini is not especially sensitive. I know that it failed my 24" silver cache test, but so did the TM808 and everything else I tried.

Geotech

What Detector Has Hit The 24"? Have You Tried big Frame PI Machines ?

1x1m

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On 4/24/2022 at 4:08 PM, Magic12 said:

Geotech

What Detector Has Hit The 24"? Have You Tried big Frame PI Machines ?

1x1m

I built a 1m x 1m frame coil for the TDI but it didn't work very well. Also made a 24" round coil for the TDI, it worked better but still didn't detect the cache.

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