metal detecting using rf waves

[ant17]

hi guys i was wondering what your thoughts are on using a radio frequency transmitter and receiver between 400mhz and
1gz to detect gold and other metals. i thought you could go deeper and search a larger areas but i am not sure how it would be possible to descrimnate targets. my only therorys are the conductivity of the metal and also maybe dielectric constant and diffrence in frequency from rx signals from diffrent types of targets

[Carl-NC]

That's the general range for GPR. Soil attentuation goes up with frequency, and GPR flat out won't work in some soils.

[ant17]

hi do you think there would be some way to descriminate

[moodz]

.. see this paper.

tdandfdemmeasure.pdftdandfdemmeasure.pdf
tdandfdemmeasure.pdf

[Davor]

For some time I'm thinking of a LF contraption that would use 2 receivers, one for ground/target and the other for air/reference signal to achieve both nice depth and discrimination. A kind of passive 2boxx. There are commercial devices for seeking underground cables/tubes/cavities at great depth that use LF transmissions, but not with discrimination that I know of.

[WM6]

hi guys i was wondering what your thoughts are on using a radio frequency transmitter and receiver between 400mhz and
1gz to detect gold and other metals. i thought you could go deeper and search a larger areas but i am not sure how it would be possible to descrimnate targets. my only therorys are the conductivity of the metal and also maybe dielectric constant and diffrence in frequency from rx signals from diffrent types of targets

At those frequencies you cannot go deeper than at VLF, just contrary and you will be able to find shape of target before its composition.
As Carl says you are here limited to work at radar principle (soil structure reflection) and not on electromagnetic induction in metallic targets.

[nelson]

mmmm.....

And what about using babies transmiters and recibers, that woks around 49 MHz

[WM6]

mmmm.....

And what about using babies transmiters and recibers, that woks around 49 MHz

It is hard to build smal (portable) and very directive antennas at those frequencies, othervise GPR principle are the same.

I am adapting pair of cheap (10euro) one chanel Walkie talkie for GPR use - for now with doubtfull results, but will try with some new ideas again.

[Davor]

I too have some ideas with PMR band exciter and a solution that I borrow from direction finding. Point is that you can obtain Dirac response at Tx, but also at Rx. While Tx approach is the way most radars perform, the Rx approach is seldom used, but there is no wideband modulation at Tx so I can use full allowed power at any ISM or CB band I want. You know, if the mountain won't come to Muhammad...

I'm not into programming lately, so my main problem is processing the data. I could do whatever I want with data in a spreadsheet, even a bit VBA programming, but I completely lost stomach for making standalone programs.

[ant17]

rf detector

thanks guys i have had some similar ideas thanks for your input and if anybody has any more input i would be glad to see it

[nelson]

Hi WM6

Here i m showing you a very small an eficiente magnetic loop that can be uses for 49 Mhz or aorund it.

Is my own expirence and hamradio friends that this antena are very powerfull.

http://www.youtube.com/watch?v=gfYX1x2aWOc

Regards

Nelson

[WM6]

Hi WM6

Here i m showing you a very small an eficiente magnetic loop that can be uses for 49 Mhz or aorund it.

Is my own expirence and hamradio friends that this antena are very powerfull.

http://www.youtube.com/watch?v=gfYX1x2aWOc

Regards

Nelson

Yes Nelson, nice 10m loop, worth to try in amateur or CB band.

For target positioning we need two RX antennas at proper distance. And still remain main problem how to separate strong TX signal from weak target reflected signal using simple amateur means.

[Davor]

For my dipl.ing. thesis I made a CW reflectometer for cable tests that preceded anritsu site master for a decade. It employed a bridge that took care of the Tx signal quite effectively. With proper distancing you'll need to reduce Tx by only 20dB or so because it will remain cyclo-stationary, whereas the targets will have responses variation over time as your cart moves.

[WM6]

For my dipl.ing. thesis I made a CW reflectometer for cable tests that preceded anritsu site master for a decade. It employed a bridge that took care of the Tx signal quite effectively. With proper distancing you'll need to reduce Tx by only 20dB or so because it will remain cyclo-stationary, whereas the targets will have responses variation over time as your cart moves.

Hi Davor, thanks for idea. But I have a little pictorial mind and I am not sure If I understand your concept properly. Can you provide us with some shematic or at least block shema of your construction?

[Tepco]

Craziest way of RF metal detection I've ever seen is “ballistic radar”, device capable to track single 7g cal 303 bullet some 2000m downrange, and measure it's velocity. May sound like high-tech, but it is not, some 30y+ machine. Technical description goes like this: around 150mW GUNN diode source, at 10.5GHz, nice invar resonator for good thermal stability and low phase noise, diplexer and mixer, to produce Doppler signal. Followed by simple but effective filter, few CA3130 amps and precise LC filtering. Computer was based on some obsolete TI 16bit microprocessor, output on LED display and thermal printer (also HPIB). RF head was something like 20cm parabolic antenna, simple portable device most probably modified old live broadcast STL link adjusted for this purpose. Later, some modified version actually worked with 20mW Gunplexer, like in door-openers. Unbelievable, I have some experience with microwaves, radars and all that, but still can hardly believe this can work (well, until I see it it in action). Imagine just all noise and interference from nearby objects, trees and all, compared to reflection of very small target. Unfortunately, useless for normal metal detection, MD's are near field devices, not based on EM radiation. RF is strongly absorbed or reflected from surface, GPR tries to solve this problem with some limitations, UWB have great potential, but for normal purposes: business as usual, good old coils and all...


(now, exceeding #300 posts I have to retire here)