Noise Cancel Frequencies

Found this very interesting frequency test on the mine lab owners site. Very interesting. Now I'd like to know if this might hold true for the Etrac.
I read a year ago something simular, but just the opposite, low number noise cancel was equal to lower frequencies on the Etrac, but in this video low noise cancel numbers were the higher frequency with the Explorer.


[www.youtube.com]

Minelab gives you the option to acomplish this manually or automatically and whatever works.

I really like the automatic and feel an Explorer can do it better automatically but then again its an option as we are all individuals.

Always remember hunting the front area of a High School and when the lights were turned on at dusk my Explorer went erratic but the simple automatic feature just made it run smooth and like magic was back to a stable unit.

If you feel you can do it better manually be my guest but the automatic feature is quick simple and works for me

I imagine same might be the same for a talented individual under extreme circumstances and guess thats why Minelab gives us that option..

................ and why this would not be advertised in the owners manual is beyond me. If this is truly the case...... it would be a major attribute/tool and a major selling point. I would adjust my frequency (via channel selection) in accord to what my surrounding conditions presented...... and what type of targets I'm looking for.

Dan, I think what Mark was getting at (moreso) is that the different channels respond differently to different targets. The lower ones on the E-Trac (from someones testing) are much lower in frequency set than the higher ones. So, low ones for silver and high ones for jewelery, for example. Of course there is the actual act of quieting down your machine as well.

Here is an interesting thread that talks about this: [www.minelabowners.com]

And from that thread I found the following post from Arihadj particularly interesting (I'm curious what Tom and others have to say about this "pulse rate". Tom has spoken of something relating to "decay rate" on an E-Trac before, similar?):

""This is something that I posted on another forum recently:

I was once told that the operating frequency of the E-Trac varied depending on the noise cancel number you were using so if you wanted to use the highest frequency then use the lowest noise cancel number. This didn’t agree with some sensitivity tests I carried out on thin pieces of foil so I set about measuring the transmit frequency with an oscilloscope (after all that’s what I do for a living), and as I suspected the reverse is true.

On noise cancel 1 there’s a burst of pulses every 0.72ms (1.39KHz) and each pulse has a rate of 45 us (22.2KHz)

On noise cancel 11 there’s a burst of pulses every 0.6ms (1.67KHz) and each pulse has a rate of 36 us (27.78KHz)

Does this mean if you want the highest sensitivity to thin hammered coins then its best to use a high noise cancel number, and for less sensitivity to foil and greater depth use a low noise cancel number? This is assuming of course that there’s no other detectors around and you have a choice of numbers.

I would be interested on other peoples thoughts and tests. ""

edit - Agree with your comment Tom. But Minelab, unfortunately, seems secretive. Typical corporate mentality, no all, but many...



Edited 2 time(s). Last edit at 02/03/2012 03:24PM by earthmansurfer.

Here is a picture of the ETRAC transmitted signal. The small pulse frequency burst is 45KHz, +/- 5KHz.



I would really like to see what a V3i output signal looks like.



Edited 1 time(s). Last edit at 02/03/2012 03:59PM by Yeasty.

Far from sinusoidal.

EMS, per your test. Is that a big enough of a spread to make a difference. Doesnt look like it to me. Maybe some?? Your thoughts??
John

Yeasty - Excuse me ignorance but what is significant in your photo? I mean what does that do to a target relative to another detector?

John - I'm a bit over my head here. I didn't test anything, it was another poster I quoted. Or do I misunderstand you? I was just hoping someone here could start to make sense of this all as far as PRACTICAL results. I think the theory part is getting covered. ;-)

EMS

The photo shows that the ETRAC signal is square waves. Square waves generate harmonics. My conjecture is that when a target is hit with them it responds with harmonics of the transmitted signal which the ETRAC recieves and sorts out target information. The Noise Cancel function varies the transmitted small pulse frequency burst +/- 5KHz. No other manufacturer does it this way.

Am I missing something here...Noise cancel to me is to have your unit run stable rel EMI etc. and whatever else would cause unstability....suppose you did find or prove one way or the other one freq. was better for gold silver or even perhaps lead and metal for you relic hunters and you were after any of the above mentioned and setting if that setting caused unstability especially after the sign and lights were turned on in my post and my unit ran unstable would I leave it at the hot number for silver if I was after silver or would I just run the automatic noise cancel to have a stable unit...I may be a layman of sorts and some of you members may be tech's of sorts but somewhere along the way you lost me and probably a bunch of other hunters as we are over analyzing at best or are we not????.

The primary function of Noise Cancel is obviously to cancel noise. In Auto Noise Cancel the machine seeks out the quietest frequency. By manually decreasing or increasing the transmitted frequency it is thought to be able to enhance the machine's response to lower or higher conductive targets. By how much is speculative. I suspect it is not much. If the manually selected frequency is being interfered with by EMI it's all a moot point.



Edited 2 time(s). Last edit at 02/03/2012 06:42PM by Yeasty.

Yeasty - Can you explain a few of these things deeper and perhaps how it can apply to detecting as well? I enjoy reading your responses.


>On noise cancel 1 there’s a burst of pulses every 0.72ms (1.39KHz) and each pulse has a rate of 45 us (22.2KHz)
>
>On noise cancel 11 there’s a burst of pulses every 0.6ms (1.67KHz) and each pulse has a rate of 36 us (27.78KHz)

The above seems to indicate that there are more frequent pulses at the lower Noise Cancel Channels AND the frequencies are lower. ( I think). Now, you say "The Noise Cancel function varies the transmitted small pulse frequency burst +/- 5KHz. No other manufacturer does it this way." Where are you getting the +/- 5KHz? What are the potential implications or results of all this? In a practical way, in my 1% highly iron mineralized soil, the E-Trac was substantially better at depth than my V3i (in 3 frequencies). All the detectors I have operated here (T2, Omgega and V3i) have had fits at around the 7" level with VDI consistency. The E-Trac was very consistent, at least with the CO number.

Thanks,
Albert

> On noise cancel 1 there’s a burst of pulses every 0.72ms (1.39KHz) and each pulse has a rate of 45 us (22.2KHz)
> On noise cancel 11 there’s a burst of pulses every 0.6ms (1.67KHz) and each pulse has a rate of 36 us (27.78KHz)

I don't recall the numbers, but these seem perfectly reasonable. There is about a 20% variation over the noise cancel range or, if you take a midpoint (Noise Cancel 6), about +/- 10%. As I mentioned in another thread, the nominal high frequency is 25kHz (which you see as the 8 high pulses) and the nominal low frequency is 1/8th of that, or 3.125kHz, which you see as a single large pulse. That's all; there are only 2 frequencies. Noise Cancel slightly shifts everything, but not by enough to make any difference on target sensitivity.

Here's a pic of the transmitted signal at Channels 1, 6, and 11. I measured the channel 6 frequency of the short pulse train, and indeed it's at 25KHz.





I might be wrong but I believe the large pulse is used for the auto gound balance and FE measurement.



Edited 1 time(s). Last edit at 02/03/2012 10:13PM by Yeasty.

Thanks for that reply Carl. I haven't found a difference on coin hits at 8" or so from changing the noise channels. I've heard on small gold there is a difference and have seen that in videos though.

Yeasty, thanks for that last pic but can you take a stab at my last question please? The pics don't have any meaning to me - I mean I don't understand that as they seem to be the same.

Thanks for your work,
EMS

Yeasty im surprised you didnt post this from Gordon; [www.minelab.com] You are right about it might not be worth while if the channel you select is being interferred with. However, EMI tends to affect the lower freqs more than the upper. The machine might be adjusting for smooth operation, but this operating freq is lower than say small gold item and the machine would still function well if manually adjusted. It would be kind of like auto sensitivity vs manual. Ive found it very odd ML refuses to post these random freqs.... unless for some reason it would be detremental to the sell of their detectors in some way. Ive never asked Ralph at Sunray he may know..... id be very surprised if Gordon doesnt have information necessary to make his post.

Dew

EMS, my last pic shows the transmitted frequency differences of Noise Cancel channels 1, 6, and 11. Notice that channel 1 is the lowest and 11 is the highest.

Yeasty Wrote:
-------------------------------------------------------
> EMS, my last pic shows the transmitted frequency
> differences of Noise Cancel channels 1, 6, and 11.
> Notice that channel 1 is the lowest and 11 is the
> highest.

I'm sorry Yeasty but I am not understanding this. It looks like some of the picture lengths are shorter - like the last long line was truncated.

Can someone help me out here? Would love to understand this and see how to apply it practically.

Thanks for your efforts Yeasty,
EMS

Facts:
Low conductor targets (gold, etc) respond better to higher frequencies
High conductor targets (silver, etc) respond better to lower frequencies
Noise Cancel #1 operates at a lower frequency than Noise Cancel #11

My WAGs:
By using Noise Cancel #1 the ETRAC would be more sensitive to high conductors (silver, etc).
By using Noise Cancel #11 the ETRAC would be more sensitve to low conductors (gold, etc).

With all that said, I use NC #1 over dirt and NC#11 over beaches. I could be wrong because the frequency differences between NC #1 and #11 are not significant enough to make a difference. But even if the difference gives me 1% improvement, I want to take advantage of it. Again, assuming that there is no EMI at my selected NC. I also assume that ground mineralization could also throw things way off.

Side Note:
I think about these things when the weather is crappy



Edited 1 time(s). Last edit at 02/04/2012 09:14PM by Yeasty.

I'm with you on your side note Yeasty! LOL (Ground is frozen here and its around 14 degrees).

I will test this more when I come across coins at 8" and deeper. So far I have played a little with coins at 8" and changing the Noise Cancel channels and I didn't notice a difference, but it wasn't in depth, so I have to do more. I believe there is a difference and testing will show us (at least in each of our own soils).

I'd still like to understand the "pulses" and such...

Albert

Arent there even differences in sensitivity to gold at higher freqs? For example an MXT is a tad lower ... around 13khz and the DFX can be 15 kHz..... yet the MXT is a better gold machine.

Dew

Andy's eTrac and Explorer book has a section on this. Can't type it here due to copyright but its in there.

2008 when I bought my waterproof expII back I tested it many many time once I started using the new pro coil on it and for the beach...NC 9 always hit better.

2009 I sold it and got a new SePro......tested it many times as well and like u, I manually set to 11 and never change it....water or dirt

Fyi

.
.
<")))))<>(