Power vs Depth - What is that really makes a detector go deep?

I hear the term power used a lot regarding finding deeper targets. I always thought about the snow storm analogy - turning on your brights in a snow storm does not help you see farther in fact in reduces your ability to see because of all the light scatter off the snow. Is it not more the receivers ability to resolve small signals that is most important not the transmit power. I am sure there is even more to seeing deep - and seeing deep with discrimination is the other half of that question. Would love to hear from the Professors of Detector U :-)

Bryanna - Nebraska

Current - New to me but not new MXT Pro and T2 SE2 - Previous Minelab Sovereign GT, Minelab Safari, Whites DFX, Whites Eagle Spectrum
Smile its a good for you!

Depends on the nut behind the wheel might be a good analogy.....

Distinguishing between the wobbling ground signal and the short blip up and down of a real target is the problem.
As a rough guide, a good machine could hit on a target that has a signal 1/20th - 1/50th of that of the ground.
Hence raw power, that disturbs the orbit of the Earth, doesn't help, as it makes all signal bigger.

Carl Moreland over on the Geotech1 Forum likens it to:
"listening to someone talking, when they're standing next to a loco sounding its horn"
Edit: This is an ANALOGY, its obvious flaw is the fact that buried targets and ground don't give any signal of their own. They do 'give off' a signal when you waft a magnetic field near them.



Edited 1 time(s). Last edit at 02/17/2015 08:03PM by Pimento.

Pimento Wrote:
-------------------------------------------------------
> Distinguishing between the wobbling ground signal
> and the short blip up and down of a real target is
> the problem.
> As a rough guide, a good machine could hit on a
> target that has a signal 1/20th - 1/50th of that
> of the ground.
> Hence raw power, that disturbs the orbit of the
> Earth, doesn't help, as it makes all signal
> bigger.
>
> Carl over on Geotech1 likens it to:
> "listening to someone talking, when they're
> standing next to a loco sounding its horn"

Since I work for the Railroad makes perfect sense :-)

Bryanna - Nebraska

Current - New to me but not new MXT Pro and T2 SE2 - Previous Minelab Sovereign GT, Minelab Safari, Whites DFX, Whites Eagle Spectrum
Smile its a good for you!

Bryanna, I recently engaged the good nerds at the Geotech forum on this Q and the link to the thread is here: [www.geotech1.com]

I think the thread answers your (and my) Q very well and in several thorough manners.

And if your technical curiosity continues, I highly recommend "Inside the Metal Detector" by Carl Moreland and George Overton

wirelessguy Wrote:
-------------------------------------------------------
> Bryanna, I recently engaged the good nerds at the
> Geotech forum on this Q and the link to the thread
> is here:
> [www.geotech1.com]
> 3-Transmit-amplification-mod&highlight=increase+tx
> +power
>
> I think the thread answers your (and my) Q very
> well and in several thorough manners.
>
> And if your technical curiosity continues, I
> highly recommend "Inside the Metal Detector" by
> Carl Moreland and George Overton

Thanks will checkout the link. I like to understand how things work. :-)

Bryanna - Nebraska

Current - New to me but not new MXT Pro and T2 SE2 - Previous Minelab Sovereign GT, Minelab Safari, Whites DFX, Whites Eagle Spectrum
Smile its a good for you!

Dan-Pa. Wrote:
-------------------------------------------------------
> Depends on the nut behind the wheel might be a
> good analogy.....


lots of "nuts" behind the wheels lately! dan!
ehe! he! he! he!

(h.h.!)
j.t.

Things like this are never simple... Moving the focus a few inches or levels of magnification, don't forget coil size (bigger is not always best, NASA Tom recommended the 10.5 as an optimal beach size on his DVD) and sweep speed as well as audio quality and ground and target variables. Then again skill and focus of the detectorist is a factor, isn't it? And everything may change by site conditions! 2 cents more free advice (musing?).

Past(or)Tom
Using a Legend, a Deus 2, an Equinox 800, a Tarsacci MDT 8000, & a few others...
with my beloved, fading Corgi, Sadie

There is Physics behind my question. My guess and it is an educated one is that transmit power is not the key to depth. It is the ability to listen to analyze the smallest of return signals. When we increase sensitivity we are making the receiver more sensitive received signals - thus the reason detectors become more noisy the higher the gain on the receiver. I think Fisher has been able to deal with this unwanted noise or at least suppress it after it is received so we can hear only the wanted signals.

Bryanna - Nebraska

Current - New to me but not new MXT Pro and T2 SE2 - Previous Minelab Sovereign GT, Minelab Safari, Whites DFX, Whites Eagle Spectrum
Smile its a good for you!

Quote:"My guess and it is an educated one is that transmit power is not the key to depth. It is the ability to listen to analyze the smallest of return signals"

No.... Read my first reply, (and the others). There is not any major problem trying to analyse small signals. If your signals are too small, use more transmit power to bring them all up in level. It's perfectly possible to make a detector that would airtest a dime at 24 inches. Small signals can be dealt with, with care. Significant ground signals can't.

Great question BryannaGirl!!!!!!

Pimento Wrote:
-------------------------------------------------------
> Quote:"My guess and it is an educated one is that
> transmit power is not the key to depth. It is the
> ability to listen to analyze the smallest of
> return signals"
>
> No.... Read my first reply, (and the others).
> There is not any major problem trying to analyse
> small signals. If your signals are too small, use
> more transmit power to bring them all up in level.
> It's perfectly possible to make a detector that
> would airtest a dime at 24 inches. Small signals
> can be dealt with, with care. Significant ground
> signals can't.

I have been reading - and I think I may be saying this wrong but from what I read the reaso we do not turn up power (talking VLF) is the ground response starts to overwhelm the good signals. So we do not change transmit power to go deeper we process the incoming signal and in simple words suppress the ground and Electo Magnetic Noise and pass the good signal from the conductor. But to increase depth do you not increase gain (sensitivity) to gain more signal.

So help me here. Is not sensitivity increasing the gain of the receiver, and does not that help see deeper targets.

Back to my original post and the snow storm analogy - Making your brights brighter (transmitt power) only increases the amount of light reflected back at the driver(coil/reciever) making it harder to see what's further down the road(deeper in the ground). So instead we can change to low beem and maybe fog lights to reduce the amount of light reflected from the snow (ground signal). Now the driver(coil/reciever) has less light noise (ground signal) so is able to pick up fainter (weaker signal) objects further down the road (deeper) to see even further we need to improve the drivers(receivers) night vision ( sensitivity to small signals) so he can see even even fainter (deeper) objects down the road.

Now that all sounded good but I know in detectors we do not change transmit power(lights) to reduce ground signal. Instead we adjust balance point of the detector so the effect of the ground is not to positive (ground reflection) or to negative - filtered. So in the above analogy we are filtering the light not changing its power so the light reflection of the snow (ground reflection) is neutral..

Am I getting closer to having this right?

Bryanna - Nebraska

Current - New to me but not new MXT Pro and T2 SE2 - Previous Minelab Sovereign GT, Minelab Safari, Whites DFX, Whites Eagle Spectrum
Smile its a good for you!

Couldn't we maybe first list/find out which detectors transmit the most power, and see how they compare in performance to say detectors which transmit less power???
I like to try and go from a known first (given) when I'm trying to figure something out (prove).

tnsharpshooter Wrote:
-------------------------------------------------------
> Couldn't we maybe first list/find out which
> detectors transmit the most power, and see how
> they compare in performance to say detectors which
> transmit less power???
> I like to try and go from a known first (given)
> when I'm trying to figure something out (prove)

The amount of power transmitted I think is very close - from what I read what limits the amount of power the unit can transmit is the noise generated by the ground. This came from a detector engineer Dave Johnson. He said that is the reason with current technology increases in depth come slowly. As Pimento said it is the ground that is the problem.

Bryanna - Nebraska

Current - New to me but not new MXT Pro and T2 SE2 - Previous Minelab Sovereign GT, Minelab Safari, Whites DFX, Whites Eagle Spectrum
Smile its a good for you!

Ok, the ground is the problem. I can agree with that. So what makes one detector disregard the ground or compensate for the ground better than the other?? Is it coil design??
Frequency?? Filtering??? Detector's ability to identify smaller signals(received)?? Detector's ability to clean up smaller signals(received)?? Detector's ability to generate a cleaner signal (transmitted)? Ground balance circuit ops (Do all really balance?)? The answer lies within one, some, or all of these, maybe?



Edited 1 time(s). Last edit at 02/17/2015 07:04AM by tnsharpshooter.

It is always about the ground. That is why so much computing power on modern detectors is taken up with dealing with the ground signal. If you really want to detect deep targets, hunt in ground with no ferrous mineralization.

The key to depth in any ground that has ferrous mineralization is found in addressing the ground response. First is alway using a detector that can cancel or null out as much of the ground signal as possible, Second is reducing the amount of ground signal the detector circuits have to deal with. Third is to keep as much of the target signal intact as possible.

If you really want to learn what is going on in a metal detector I would recommend that you buy a used DFX and have a go at learning the components of detector design and functionality first hand.

HH
Mike

Quote:"[so] the reason we do not turn up power (talking VLF) is the ground response starts to overwhelm the good signals"
No.....turn up the TX power, the ground responce goes up, the target response goes up. Both in perfect sympathy. So you've improved nothing.

The fog/headlights analogy is a poor one, avoid it.

For some bedside reading, buy a copy of the book:
"Inside the metal detector" by George Overton and Carl Moreland

And have a look here:
[www.minelab.com]

Basic MD operation
Ground mineralisation,
MD basics and theory

My once only edt:
The XP Deus coils have three levels of transmit 'power', user selectable. The resulting voltage on the TX coil are something like 40%, 63%, 100%. The receiver side of things is [in my opinion] adjusted in sympathy: 100%, 63%, 40% (done in software, I suspect).
Most users report no difference in air or in-ground 'depth'. If there's EMI about, the higher power would be a good choice. If you want maximum battery life, the lowest power would be your choice.



Edited 1 time(s). Last edit at 02/17/2015 10:20AM by Pimento.

Dave J said the transmit power is at max now. You would need 100×the battery power to increase it. Its not simple. Big engineers have tryed to solve this problem. Look at some of his essays on the fisher web page.

Ok its 4096 more times battery drain to double the signal output. Look at his Q&A on fishers web page.

Sigh. No... It's 4096 times the battery drain to double the depth, assuming all you did was simply up the TX 'power'. And this is in AIR.



Edited 1 time(s). Last edit at 02/17/2015 03:12PM by Pimento.

Pimento Wrote:
-------------------------------------------------------
> Sigh. No... It's 4096 times the battery drain to
> double the depth, assuming all you did was simply
> up the TX 'power'. And this is in AIR.

I really don't like talking out of my butt that's why I reread the article on fishers web page.

Here's the quote from the article:
"If everything else is maintained equal, doubling the depth requires 64 times as much signal. If this is done by increasing transmitter power, doubling depth requires 4,096 times as much battery drain"

The full article:
[www.fisherlab.com]

It's rather an attention-grabbing statement, as the idea of sticking 400 volts on a search-coil is a bit scary, not to mention the 100 Watts of heat produced will smoke the coil in seconds!

Lol yes it sounds scary.

hard to quantify as soil varies greatly around the world

But it seems that the detectors can send a signal deep enough. As was mentioned in another post 2ft holes - too deep unless you truly knew there was a silver at the bottom. I do not think it is not so much about getting more depth as it is getting depth with usable target information. Once we get much over a foot we are no longer digging we are excavating. So we really need to know more about the target before we make that investment in energy. I guess the exception is areas where you already know what you will be finding at depth then it may be worth the effort. So we need smarter detectors not so much deeper. An F75 can hit Keith's 13.5 inch Nickel with no problems. But what if it could hit it and tell you with high confidence it is a nickel - then we start to have something. I know in the right ground the FBS machines can tell you a lot about the target buried Deep. So I think we will see better and better target ID info as technology progresses.

Bryanna - Nebraska

Current - New to me but not new MXT Pro and T2 SE2 - Previous Minelab Sovereign GT, Minelab Safari, Whites DFX, Whites Eagle Spectrum
Smile its a good for you!