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No, it's too much trouble to look up. You can find it yourself in the US patent office.Originally posted by WM6
Best wishes,
J_PComment
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I was trying but nothing. What is PAT Nr. or Subject?Originally posted by J_Player View PostComment
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This was my first attempt but no success.Originally posted by mikebg View Post
Only keyword from schematic that lead to more real data is "MFS-14790".
It return:
"Detection and location of metallic objects imbedded in nonmetallic structures
Author(s): Brown, R. L.; Neuschaefer, R. W.
Abstract: Small battery operated eddy current proximity measuring device detects and locates metal objects the size of a dime at distances up to one foot within nonmetallic structures. This device weighs approximately two pounds, ... etc."
It is about NASA internal (but public domain now) paper, seems not patented and not digitalized yet.
J_Ps patent claim is probably sort of his "Examiner test" misleading story.
Comments on schematic can be from one of authors (Brown) personally.
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"Detection and location of metallic objects imbedded in nonmetallic structures
Author(s): Brown, R. L.; Neuschaefer, R. W.
Abstract: Small battery operated eddy current proximity measuring device detects and locates metal objects the size of a dime at distances up to one foot within nonmetallic structures. This device weighs approximately two pounds, ... etc."
This?:Comment
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I started a new thread "BLACK HOLE ANTENNA" in section "General Electronics". It will be discussed the SPICE simulation of wrong circuit diagrams. This is very educational because SPICE can't detect design errors. The designer should think carefully when set a circuit diagram for simulation.
To undestand the future postings, you should search WEB and read in advance all about theory of "Q-multiplier".
Mike-BGComment
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Yup. This is not patented or in the US patent database. For sure. It would be interesting to track down the paper.Originally posted by WM6 View PostComment
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I checked my private database for this Eddy current detector. Here is a screenshot of what I saved several years ago.Originally posted by technos
The source page is still online here: http://ntrs.nasa.gov/search.jsp?R=43...N%3D4294956547 but does not show the image.
You will see there are links that lead to sites where you can order the full 13 page article from the NASA tech briefs.
I believe this device was also patented.Comment
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The use of 2 ferrites appears in Van Oort's article. This metal detector requires for good performance 2 ferrites pieces of exact characteristics. The author suggest that cut the both pieces of ferrite from an unique piece. I think that for the NASA's ferrite detector is useful that the both ferrites will come from an unique piece (cut) or equal ferrites from the same manufacturer. In the Van Oort's article also are used other small ferrites pieces for compensation, include bronze screw...Comment
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The block diagram is specific case of IBR MD
If we know the correct block diagram of an operating prinzip, we have a powerful tool for design and to detect drawbacks of an existing design. We have the correct block diagram of REGEN prinzip given as posting # 116 in thread "Popular Electronics". The NASA circuitry MFS-14790 has the attached here block diagram. If we compare both, should find that NASA circuit have less sensitivity because of low amplifier gain and very low frequency shift because of steep phase characteristic formed by both tank circuits L1-C1 and L2-C2.
I will post soon an analysis of maximal amplifier gain for ideal BALANCED REGEN metal detector.Comment
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@Bill512
Thank Yo big time
for the professional and best explanation. I will look to find out more about that "Magnetostriction effect". The iron does oscillate on the same audio-frequency but with different input kHz signals the Fisher 1266-X and Garrett Ace 250 uses.
@ J_Player
Thx for the NASA schematic.
@ mikebg
Are you from Bulgaria? I wanna go search emeralds there in the Rila - Borovets Region. Can you tell me more about it?
@ all:
Attention: Extremly big coincidence!!!
Believe it or not, but today in the very early morning I did found a NASA Matchbox toy-car together with 2 other interresting objects. 
Found them with my modified Fisher 1266-X: http://www.geotech1.com/forums/showthread.php?t=16453
Maybe this is a sign of fate we seriously should care about that NASA circuit!! btw. I really hope sometimes we can develope a MD with reflector like a satellite-dish. Because it is a completly waste of EM-Radiation Engergy if the power goes lost in the up direction. Waves are reflectible, even kHz ones.
For an efficient MD the waves has to be bundled and focused as much as possible, and it doesn't matters much what kind of material the reflector is, as long as the coils have a good adjustment and electronical balancing.Comment
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