I didn't need another project -

[ivconic]

Interesting remark, Eric.
I never think about UHF solution with hypodermic needle problem, cause UHF antennas are usually
lead over surface at greater distance from soil, than PI or VLF coils.
So we need to rethink near to soil UHF antenna movement and possible exclusion near soil impact.
Your suggestion could be real solution, cause dangerous discarded hypodermic needle in play
and park lots around schools and kindergarten are by rule not buried in soil, but only hidden in
grass and sometimes very shallow covered by sand in sandboxes.
Thanks. So Pi technology is practically excluded, same as VLF/IB in searching for hypodermic needle
detecting solution.
I will rethink suggested UHF way. You mentioned here needle resonance and not GPR like reflection.
Hypodermic needles are of different lengths, which lead to conclusion that UHF antenna should emit
sweeped frequency spectrum to resonate with needle about 3 to 7cm body length.
Here we are talking about 5 to 10GHz frequency sweep to catch most needle resonances.

You shall give it up by now... as i recall this is old attempt from several years back.
Tinkerer "poured water in my ears" (local saying) several years ago with same demands, talking about millions of euros for such project.
This would be indeed millions of euros project... if possible to be done.
Ain't no wonder why bustards from weapon industry are using similar needles for their plastic undiscoverable mines.
Such detector would be most sold product on planet. Sad fact.
GPR domain is also explored and exhausted well by now. It has its own limits.

[Ferric Toes]

Interesting remark, Eric.

I never think about UHF solution with hypodermic needle problem, cause UHF antennas are usually
lead over surface at greater distance from soil, than PI or VLF coils.

So we need to rethink near to soil UHF antenna movement and possible exclusion near soil impact.

Your suggestion could be real solution, cause dangerous discarded hypodermic needle in play
and park lots around schools and kindergarten are by rule not buried in soil, but only hidden in
grass and sometimes very shallow covered by sand in sandboxes.

Thanks. So Pi technology is practically excluded, same as VLF/IB in searching for hypodermic needle
detecting solution.

I will rethink suggested UHF way. You mentioned here needle resonance and not GPR like reflection.
Hypodermic needles are of different lengths, which lead to conclusion that UHF antenna should emit
sweeped frequency spectrum to resonate with needle about 3 to 7cm body length.
Here we are talking about 5 to 10GHz frequency sweep to catch most needle resonances.

Attached is a description of the workings of the UHF detector. This is from an article in the Electronics World magazine for December 1966. There is no indication of how small a metal object can be detected and I don't know of any actual devices that work in this way. You would think that developments of this technique had progressed since 1966
The resonance method might be worth investigating and, as you say, a frequency sweep method and a spectrum analyser for a Rx display. Objects at resonance should appear as a spike on the display.

Eric.

[ivconic]

US5936586A

[ivconic]

Obvious nonsense.
Chasing a fog.
Various propagations (world we are currently living in) will overwhelm any tiny signal coming from such needle in a grass.
Even grass itself will choke it.
Aware of "wet&dry grass effect" at VLF I/B's?
"Doppler-ing" at UHF will be 100x more horror.

[ivconic]

But than again... i can imagine the rough contours of such design yet.
Since there is one very significant and important factor here; the target is already known, with all its features.
Whenever i think on propagations, hum and "dirt" in the air that surrounds us: i also recall the way how small digital radio packets are functioning.
GSM for example. WiFi too (BT too).
Small power, yet effective, long range and accurate.
Since the target is well known; maybe is possible to "memorize" it in a short radio data packet like that.
The rest of the story is easy to anticipate...
But i don't need to give you all on the plate now...

[Ferric Toes]

Still no schematic?
This topic will bust!

There will be no schematic until this project is finished!! I am making changes and additions each day, so there is no point. Guidelines for this forum are:- General tech discussions on all types of metal detectors: VLF, PI, 2-box, BFO, off-resonance, PLL, etc. Questions, ideas, and anything else that moves you. It does not say that schematics should be attached to any technical discussion. I have the intellectual property rights to what I am doing for my own interest and it is purely at my discretion as to what is shared and when. Same goes for everybody.

Eric.

[Qiaozhi]

There will be no schematic until this project is finished!! I am making changes and additions each day, so there is no point. Guidelines for this forum are:- General tech discussions on all types of metal detectors: VLF, PI, 2-box, BFO, off-resonance, PLL, etc. Questions, ideas, and anything else that moves you. It does not say that schematics should be attached to any technical discussion. I have the intellectual property rights to what I am doing for my own interest and it is purely at my discretion as to what is shared and when. Same goes for everybody.

Eric.

Just carry on Eric.
Ignore the negativity of some posts.

I've been searching for that UHF detector article from which you posted an extract. Cannot find it anywhere in the internet archives.

[ivconic]

There will be no schematic until this project is finished!! I am making changes and additions each day, so there is no point. Guidelines for this forum are:- General tech discussions on all types of metal detectors: VLF, PI, 2-box, BFO, off-resonance, PLL, etc. Questions, ideas, and anything else that moves you. It does not say that schematics should be attached to any technical discussion. I have the intellectual property rights to what I am doing for my own interest and it is purely at my discretion as to what is shared and when. Same goes for everybody.
Eric.

Eric you really do not understand my point here!?
I don't give a squat about that schematic, really.
I have several versions of that schematic, for years back, probably among the very first schematics that i collected in deep past.
Having it so long ago; i never even payed attention on it nor tried to replicate it.
It is not the point.
Point is in indeed interesting phenomena that NO ONE from the known "great designers" (including you on the first place when we talking about PIs) will ever show good will to disclose any of production papers.
No matter how old the design is. No matter how obscure and irrelevant the design is too.
NO ONE from "officials" will ever show even slightest good mood to share similar documentation. Even if it is dated 50 years back. Discontinued, abandoned etc.
That's my point all the time here. I find this as indeed fascinating phenomena.
I am here since 2006. 14 years and still haven't seen the exception. Except Carl in few rare cases.
I find this as amazing phenomena.
Even with you now. This is fantastic!
You've been circulating one and pretty much the same circuit and design for years. In various shapes, models, brands.
Already disclosed totally. Known. Reverse engineered by many.
No secrets at all. And yet you are resisting hard even on such benign demands!??
I find this amazing! Fascinating!
That is my point here all the time. But you don't understand it.
I think that such kind of "paranoia" kills any chance for this hobby to progress more.
Also makes even wider gap between people like you and majority of hobbyists.
Of course.. ain't nobody else that crazy as me to tell this directly in public.

[ivconic]

Just carry on Eric.
Ignore the negativity of some posts.

I've been searching for that UHF detector article from which you posted an extract. Cannot find it anywhere in the internet archives.

C'mon Q !!!
By now you should know me better than that!
There is no negativity on my side at all.
Production paper which is 40-50 years old, discontinued, obscure, abandoned, irrelevant... why not sharing it with community here?
What's the problem?
No negativity. Only confusion.
Incredible interesting phenomena too.

[Ferric Toes]

Just carry on Eric.
Ignore the negativity of some posts.

I've been searching for that UHF detector article from which you posted an extract. Cannot find it anywhere in the internet archives.

I found this on the internet but, as yet, not the article. I can copy mine and send it as it is very interesting considering so long ago. Eric.

Lancaster Donald E.

Electronic Metal Locators, Basic Types and Design Factors

Electronics World

Dec. 1966

pp. 39-42 and 62.

excellent revievs of operating methods (no P.I.), good text, many block diagrams

[ivconic]

Don't bother.
https://worldradiohistory.com/Archiv...ld-1966-12.pdf

[ivconic]

Extracted:

[Qiaozhi]

Don't bother.
https://worldradiohistory.com/Archiv...ld-1966-12.pdf

Thanks. No wonder I couldn't find it, as it was in the American Electronics World version, not the UK one.

[ivconic]

It is not best possible copy, yet good enough for overview.
If it was of a grater value for me; i would pass it through the OCR and make proper fine document... but is not.
OCR is not perfect and sometimes demands additional labor.
That's why i processed only part of the last page, which interests WM6 mostly.

Electronic Metal Locators
(Continued from page 42)
U.H.F. Type
This metal locator has several unique operating features. Fig, 6 shows the block diagram. The u.h.f. locator is capable of detecting either metallic or non-metallic objects and is able to discriminate between these objects and the normal clutter of rock discontinuities. Operation is somewhat similar to the induction-balance locator, except that the operating frequency is 400MHz and the loops are replaced in a search array consisting of inductively loaded dipole antennas.
Two transmitting dipoles are used with a receiver dipole between them. A figure-eight pattern is produced in the absence of any target, resulting in balanced voltages that nearly cancel in the receiver dipole. The presence of any object of uniformly different conductivity and dielectric constant from the surrounding medium upsets the balance and produces an output signal. There are two modes of operation, the "Search" mode and the "Point" mode. In the "Search" mode, all of the spurious return is averaged out by a long time constant a.g.e. loop, while any sudden changes in the field patterns are greatly amplified by an expander circuit, indicating the edge of a target direct below the search array. In the "Point" mode, the receiver output is amplitude-sensitive and the instrument may be used to outline the buried object. The u.h.f. locator is principally used by the military for the detection of metallic and non-metallic mines.

[Carl-NC]

Thanks. No wonder I couldn't find it, as it was in the American Electronics World version, not the UK one.

And it was right here on Geotech the whole time:

https://www.geotech1.com/cgi-bin/pages/common/index.pl?page=metdet&file=info/lancaster/index.dat