Can someone confirm this?

I posted this on the official Minelab forum and got a very surprising answer.


This is a quote from page 11, of Andy Sabich's book, The Minelab, Explorer & Etrac Handbook



"Unlike the BBS circuitry
which spaced each
frequency by 1.5 kHz, the
FBS circuitry could select
one of 11 possible "sets"
with each providing a
slightly different spacing
between the 28 frequencies
and the upper and lower
frequencies. The benefit
this provides was that
unlike detectors that use
one or two fixed
frequencies which can be
adversely affected by
varying ground conditions or outside interference, the Explorer could pick the optimal set of
frequencies to best handle the precise conditions present at the hunt site. This is done automatically
in less than 30 seconds through the use of the NOISE CANCEL touchpad on the control housing face
(or manually through the NOISE option accessible through the menu system).


This statement is better than I thought. My thinking was that you have a constant 28 frequencies being used all the time, but his writings state the machine actually adjust the spacing of the 28 frequencies according to the noise cancel setting chosen. So the actual frequencies will change with each channel chosen by the noise cancel feature.


The replying quotes states that the Explorer and Etrac only use two frequencies eventhough they advertise 28. They are stating the this is proved by the use of scope.


"If you look at the oscilloscope reading in the other post about sens you see two frequencies.

The Minelabs seems to be transmitting two frequencies at a time and use 28 as advertising boost. There is always alot of harmonic spill off that can be used as such But there is only two main frequencies running any given time. "

It's obvious that FBS technology transmits a level pulse train. Since pulses generate a wide range of harmonics (sidebands) I suspect that Minelabs' magic is sorting out the sidebands to determine the conductive and ferrous properties of a targets' signal and assign numeric values to each. What this means is that Minelab has solved the age old problem of using single frequency transmitted pulses and extracting conductive/ferrous information from the received signal.
But then again, I could be wrong.



Tom being an electronics expert should be able to prove or dis-prove this statement.



_________________

Certainly not a technical answer but I was under the impression when you arrived at the site you noise cancelled, saw the dirt color change or have interference noise cancelled again and if you changed sites same procedure.
This seems like manual changes to me unless the unit has the unit has the ability to slightly change within the parameters of your original noise cancel..I just reread that and said HUH myself so lets have Tom make a stab at it...

Confused/incongruent statement. "Noise Cancel" is for airborne noise (EMI).....and you must hold the coil completely still/stationary. This obviously has nothing to do with 'ground' or 'dirt'.............of which..............the coil would require sweeping motion over the dirt......so as to change frequencies to best suit the dirt/mineralization. What am I missing?

The way I took it was that it would adjust the frequencies based on the "noise cancel" meaning if there is interference, it would shift the receiving frequency to a more optimum setting.

Tom is correct, noise cancel is to be performed with the coil 1 to 3 feet above the ground. It selects the best Freq that are preset on 10 different channels for the EMI that is present. So ground change does not
require a new Noise cancel. Just when you get close to power lines, Houses, buildings etc....


Tom in SC

GO GAMECOCKS, 2011 CHAMPS

Only time you should need to noise cancel on the ground is when EMI is coming from under ground as in buried power or communications cables....

I seldom need to noise cancel - only when I'm hunting with another Explorer or ETrac user. Also, someone I trust told me that the FBS patent says that three frequencies are chosen and used based on live feedback.

TOM, read this article posted on the Minelab web site and you'll see there is more to noise cancel than just EMI. I know they start off talking about sensitivity settings, but read to the end.


[www.minelab.com]





NASA-Tom Wrote:
-------------------------------------------------------
> Confused/incongruent statement. "Noise Cancel" is
> for airborne noise (EMI).....and you must hold the
> coil completely still/stationary. This obviously
> has nothing to do with 'ground' or
> 'dirt'.............of which..............the coil
> would require sweeping motion over the
> dirt......so as to change frequencies to best suit
> the dirt/mineralization. What am I missing?

Tom...plain and simple...does the Explorer series have the abilities to change frequencies on the swing(no pun intended) for us layman to handle the ground..
As far as noise cancel seems to be a difference in opinion some say flat on ground motionless which would to me indicate a sort of ground balance or several feet off the ground motionless which to me would indicate EMI..
Inquiring minds would like to know your opinion....
Finally does it run on two frequencies one for the ground and one for the EMI also comes to mind..
I know technician to layman must be frustrating at times but we are all trying to learn and heck someone has to do it...

The minelabs cant be operating on 28 frequencies as we know frequencies from other manufacturers. Then we would have both excellet sensitivity on silver and on gold nuggets at the same time. But we have not.

The depth and id capability on high conductors on non masked targets are top notch. While depth and sensitivity to small nuggets is useless. Very high conductive biased so the main peak frequencies has to be on the lower range of what we are used to.

I believe the noice cancel actually change frequencies for you as you manually go through the 10 channels. 2 or 3 peak frequencies are addressed to each noice cancel number.

You can actually try this with both a very low conductor like a small gold jewelry item and a silver dime.

Adjust noice cancel to see what nr has best sens on the jewelry and what has best sens on the dime.

I believe you are thinking along my side. The post on the Minelab site [www.minelab.com] confirms what you are saying. The article states, if you are running in manual sensitivity with low discrimination and conductive tones the noise cancel needs to be set from 1 to 4. Now if the noise cancel only adjust for EMI why would this be.

Noise cancel..................this is F1 - F7 on the T2's/F75's...............will 'shift' the operating frequency of the unit .... by a VERY slight amount......which may have a dramatic effect on EMI. The same case holds true for the Minelabs...........changing channels will VERY minutely' shift its operating Freq ( in this case.... operating freq(s).)....... for more stable operation. In concert...........this frequency channel....appears to alter how the unit responds to (in particular) small/deep conductors.........especially in manual Sens mode.

I am uncertain (without reverse-engineering) if the Explorers/E-Tracs utilize all 28 freqs at all times.........or selects a 'sub-set' of those 28 freqs. It could simply be a dual-freq unit......or maybe utilize 3 freqs. In any case...........it's designed for Aussy high-mineralization lateritic bad dirt.

Also.........of honorable mention........I believe the Explorer/E-Trac is in a 'form' of a 'salt' mode at all times.........as you can walk straight into wet salt....without changing anything on the control panel. It may be multi-freq platform driven utilizing complex waveform analyzation........or simply 'phase shifted' all of the time....in a 'salt' mode phase. Hence; it's insensitivity to small low conductors. A small (paper thin) silver coin .... does not quite constitute 'low conductor'. A small (paper thin) gold coin of the same size.... would be another story.

He didnt say it adjusts the freqs... he said those freq are RANDOMLY set unlike the Sov that is set at evenly at 1.5. I believe it was on this site that someone really explained how it worked. They discussed that it used the BEST two and one was used for ground i believe.... so basically 3 freqs. Ive talked to ML and tried to get the tech to tell me the settings for each of the 11 channels. Obviously knowing if channel one has the all randomly set near the 1.5 frez and 11 has them higher they could be an advantage to self set them.

Dew

Dewcon may be correct.
From what I have heard, ML uses one frq to sort of take a reading of the ground and uses
2 other frqs to do the work.
I have noticed decreased depth on certain channels, this was done by me many years ago.
The best I can remember, several of the very low numbers and 2 or 3 of the highest numbers.
So I don't use auto noise cancel and start out at 5 or 6 and if I have no problems I leave it there.
I also noticed I could do a auto noise cancel at the same exact place and would end up with 3 different settings....
I may have actually ended up with more than 3, it has been a long time ago when I was doing that.
Tom is correct also in that the channels are more or less a slight shift so a change of a point or 2 will likely not matter
unless there is significant electrical interference at work.
I think ML engineered it so that it wouldn't be as sensitive on very low conductors on purpose since it would likely
be difficult to control interference......ever notice high frq detectors tend to have more trouble with interference?
Yet no doubt the ML's multis will still freak out at times around a bunch of powerlines....

I have nearly always performed a Noise Cancel on the Minelab..............with the mindset that 'this is the correct thing to do' ,,,, especially since the owners manual recommends it. And now.........this may not be the case......especially if you are seeking a certain conductive-band of targets............say; 'silver'........a high conductor............or alloyed gold...... a low conductor. Indirectly........it may infringe upon a trade-secret if Minelab were to publish the data for each channel intent.

TOM, could a person disconnect the connector coming from the unit and hook up a oscilloscope and run through each channel and find the information that way?


NASA-Tom Wrote:
-------------------------------------------------------
> I have nearly always performed a Noise Cancel on
> the Minelab..............with the mindset that
> 'this is the correct thing to do' ,,,, especially
> since the owners manual recommends it. And
> now.........this may not be the
> case......especially if you are seeking a certain
> conductive-band of targets............say;
> 'silver'........a high conductor............or
> alloyed gold...... a low conductor.
> Indirectly........it may infringe upon a
> trade-secret if Minelab were to publish the data
> for each channel intent.

No need to disconnect the coil. All you have to do is wrap a couple loops of wire around the coil while the machine is on and hook up the scope to the wire. Scope signal input to one end of the wire and ground to the other. The coupled signal shows up nicely. Here's a pic of the ETrac transmitted signal I took using my scope :
[p.briggs.home.comcast.net]

I would be very interested in what the V3i transmitted 3 frequency signal looks like using this method.

Welcome Yeasty,
Will you explain what the dashes represent? Am I looking at sent frequencies? What does the scope show when there is a metal target involved? Very interesting.

What you see is the recurring magnetic square pulse train transmitted by the ETrac. This is the signal sent into the ground and is not affected by a target. I haven't been brave enough to break into the wiring to monitor the return signal of a target.

THE FOLLOWING IS FOR TECHNO-GEEKS ONLY!!:

Here is the transmitted waveform again:
[p.briggs.home.comcast.net]

What I have seen when NOISE CANCEL is set to 1 the pulse train repeats itself every 420usec (2381HZ) . When NOISE CANCEL is set to 11 the pulse train repeats itself every 350usec (2857HZ). When I measured the short pulses only, they are 22usec wide (45.45KHZ) when NOISE CANCEL IS set to 1. With NOISE CANCEL at 11 they are 18usec wide (55KHZ). Remember, this is the transmit signal. I have no idea what goes on in the receive side of the machine when NOISE CANCEL is changed. I find it interesting is that each increment of NOISE CANCEL changes the short pulse frequency by 1KHZ.
The NOISE CANCEL function is the only control which affects the transmitted signal. All other MENU functions only vary the display or received signal properties.
My WAG is the conductive/ferrous properties of a target are measured from the short pulses and the data is processed during the wide pulse.



Edited 1 time(s). Last edit at 07/02/2011 01:48AM by Yeasty.

Right up my alley!