Emi Vs Smf

[JCR]

You might want to take a little time and prove to yourself what kind of depth you get in SMF modes with low levels of Sensitivity. I mean in the ground, not air. I think it will surprise you.  This is a comforting thing to know because it allows you to have confidence in your detector and not second guess yourself when you have to really run it low.  With the level of trash you mention, a low to very low Sensitivity setting will be a two fold step in the right direction. You mentioned going below 15 with no success. Try it  all the way down just to see if it will settle down enough to hunt. You may just have to find a point where you can listen through the noise. Pitch tone may help also.

Chase mentioned Recovery speed adjustment to help with EMI. It will, but my experience with the Legend has been Lower settings help mitigate, not higher. It may very well depend on the type of interference. It would be more important to set Recovery to handle the Ground conditions as it’s primary focus.

[HardPack]

44 minutes ago, JCR said:

You might want to take a little time and prove to yourself what kind of depth you get in SMF modes with low levels of Sensitivity. I mean in the ground

The EQX 900 manual on page 25 suggests adjusting the Sensitivity level if some audible noise remains after Auto Noise Cancel. So it appears Sensitivity is not just for ground noise. Also Manual Noise Cancel may help in areas with lots of electrical interference. I may be spending some time adjusting & balancing to see if there is method to fine tune the machine.

[JCR]

If there is an Audio Gain feature try lowering that also.

[HardPack]

11 hours ago, JCR said:

If there is an Audio Gain feature try lowering that also.

On the ML EQX 900 no gain control only volume.

[GB_Amateur]

22 hours ago, Chase Goldman said:

...you can try some Hail Marys like increasing recovery speed,...

14 hours ago, JCR said:

Chase mentioned Recovery speed adjustment to help with EMI. It will, but my experience with the Legend has been Lower settings help mitigate, not higher.

I was detecting a curb strip with underground power lines buried in it.  I don't remember what mode, but probably Park 1 multifrequency.  When I lowered the RC from 5 to 4 I got a quite noticeable improvement in EMI noise, enough to allow me to detect (but still with a bit of EMI noise).

However, Hardpack mentions considerable iron trash and that often means faster recovery speeds, so there may be a tradeoff.

With the Eqx 800, when the EMI was unbearable in multifrequency (at least down to sens of 15), I found that 10 kHz, 15 kHz, and 20 kHz worked best, staying away from the extremes.  So far the Manticore has been much quieter for me, but I've still not given it the anything close to the workouts the Eqx 800 got.

[Chase Goldman]

17 hours ago, HardPack said:

So it appears Sensitivity is not just for ground noise.

It's not for ground noise, no one said it was..  What JCR was saying is don't rely on air tests to determine your depth loss with reduced sensitivity, you need to see what you depth loss is with targets actually in the ground.   In other words, you may see significant reduction in air test results with reduced sensitivity but your actual depth loss in the ground may be much less.

Folks, since EMI is such a situation specific thing with plenty of exceptions to the rule depending on hundreds of different variables, please focus less on which way I recommended you should tweak operating frequency or reactivity/recovery and just know those are parameters that you can tweak to potentially get relief and experiment by turning the knobs in either direction to see what works.

Regarding the SMF modes on Nox, the Park/Field "1's" are low frequency weighted and the Park/Field "2's" are high frequency weighted, Beach 1/2 is low, and Gold 1/2 are equivalent and high weighted.  HTH.

[HardPack]

“ The Equinox Series detectors are highly sensitive and have adjustable Sensitivity. Setting the correct Sensitivity level for individual detecting conditions will maximize detection depth. “  ML EQX 900 manual Page 18.

So is Minelab saying the stronger the transmit signal the stronger the return signal. The higher the ground mineralization the higher return ground noise. If so then reduce Sensitivity level?

“Note: While Auto Noise Cancel selects the ‘quietest’ channel based on several criteria, the selected channel may still have some audible noise. To try and reduce noise further,  consider adjusting Sensitivity.”  “ Auto Noise Cancel: #1 Hold the coil stationary and away from the ground.”  ML EQX 900 manual Page 25.

So what is being adjusted here with the Sensitivity settings. Does EMI affect detection depth. Should the coil be held away from the ground when adjusting the Sensitivity level?

I do not engage in air tests, nor has it been a topic on this post.  Thank for your reply.

[Chase Goldman]

On 12/7/2023 at 6:52 PM, HardPack said:

“ The Equinox Series detectors are highly sensitive and have adjustable Sensitivity. Setting the correct Sensitivity level for individual detecting conditions will maximize detection depth. “  ML EQX 900 manual Page 18.

So is Minelab saying the stronger the transmit signal the stronger the return signal. The higher the ground mineralization the higher return ground noise. If so then reduce Sensitivity level?

The Sensitivity setting only adjusts the gain of the signal as sensed by the receive coil it has no impact on the power/strength of the magnetic field transmitted into the ground by the transmit coil.  This received signal is a combination of ground noise, EMI, and target signal.  Hence, increasing sensitivity increases all of the above (i.e., target signal +  noise (EMI and Ground Noise)) but it does not increase or decrease them by equal amounts.  If your target signal to noise ratio is high, then increasing sensitivity generally increases detection depth.  If your noise floor is relatively high compared to your target signal (i.e., a low signal to noise ratio) and is continuously present due to EMI and EMI noise cancel is not effective, then lowering sensitivity from say 20 to 15 may decrease continuous but lower amplitude EMI noise to a sufficiently low audible level such that you can retain the SMF mode or operating frequency you want for your desired target objectives while still being able to detect targets at reasonable depths (though there will be some loss in detection depth).  If this doesn't work. You can potentially mitigate EMI further by adjusting SMF mode or switching to single frequency and adjusting frequency or by adjusting recovery speed or notching out specific target IDs where the noise is prevelant.  The latter may be impractical as EMI can show up simultaneously across multiple target IDs or affect specific target IDs of desirable targets.

Ground noise typically manifests on the Nox as continuous noise with IDs in the -7 to -9 range and is generally mitigated or completely cancelled by doing a proper Ground balance first and foremost.  If mineralization levels are high, using a coil with a smaller footprint helps to mitigate Ground feedback as does lowering transmit power.  However, on the Nox, the user has no ability to independently adjust transmit power. Beach 2 does have reduced transmit power compared other modes to better handle black sand and high salinity conditions.  In addition, the Beach modes can sense extreme changes in mineralization due to Black sand and will automatically reduce transmit power and provide an onscreen notification to the user (see p. 13 of the 900 user guide).

Using tracking ground balance can help mitigate ground noise "spikes" when ground conditions are highly variable due to mineralization or moisture content variations in the field or due to black sand or salinity level variations in surf.

Regarding the specific section you quoted above and to answer your question, ML is saying nothing explicit about transmit signal or ground noise in this sentence.  ML is only pointing out the basic relationship between sensitivity and how it directly affects target signal strength and hence target detection depth as I described above.  Transmit power does affect detection depth, but adjusting sensitivity has no impact on transmit power.  And, if EMI noise is present, increasing sensitivity may be counter productive while decreasing sensitivity may be beneficial as both signal and noise are amplified or attenuated (though at different rates) as you raise or lower sensitivity.  

On 12/7/2023 at 6:52 PM, HardPack said:

 

“Note: While Auto Noise Cancel selects the ‘quietest’ channel based on several criteria, the selected channel may still have some audible noise. To try and reduce noise further,  consider adjusting Sensitivity.”  “ Auto Noise Cancel: #1 Hold the coil stationary and away from the ground.”  ML EQX 900 manual Page 25.

So what is being adjusted here with the Sensitivity settings. Does EMI affect detection depth. Should the coil be held away from the ground when adjusting the Sensitivity level?

Regarding what is being adjusted here, see my previous discussion on how the sensitivity adjustment affects the received target signal and the components of noise (ground noise abd EMI).  EMI can affect target depth in the sense that it can overwhelm faint target signals at the limits of detection.  There is also a phenomenon known as "silent" EMI that can interfere with the detectors' receiver in a manner that effective target signal sensitivity is reduced (with a commensurate reduction in effective depth performance) without audible noise being heard by the user.

The reason ML states that the coil should be held away from the ground is to maximize the received EMI noise signal (and to also eliminate any ground noise effects) so the noise reduction channel scan is more effective in finding the receive channel with lowest detected EMI.  If you have an idea of where the most prevelant source of noise is coming from, pointing your coil in that general direction during the noise cancel routine can be effective.

On 12/7/2023 at 6:52 PM, HardPack said:

I do not engage in air tests, nor has it been a topic on this post.

In a previous post, you specifically quoted JCR who WAS referring to depth reductions in air vs. ground as a result of sensitivity adjustment reductions, in which you appeared to be confused by his mention of "the ground" as it relates to ground noise, so that's why I mentioned Air Tests previously (to clarify JCR's intent in the statement you quoted and that appeared to confuse you).

HTH

[midalake]

I hunt in mineralized black sand 100% of the time. I do not care what MF detector you are talking about. 

You need to strike a balance that will allow you the highest sensitivity for fringe targets. Mineralization REQUIRES high sensitivity to penetrate it. Without sensitivity all you lose is depth with mineralization.  

One has to understand the difference of mineralization noise and deep fringe targets. There is no such thing as trying to run silent in mineralization and getting deep fringe targets. 

[Chase Goldman]

22 hours ago, midalake said:

I hunt in mineralized black sand 100% of the time. I do not care what MF detector you are talking about. 

You need to strike a balance that will allow you the highest sensitivity for fringe targets. Mineralization REQUIRES high sensitivity to penetrate it. Without sensitivity all you lose is depth with mineralization.  

One has to understand the difference of mineralization noise and deep fringe targets. There is no such thing as trying to run silent in mineralization and getting deep fringe targets. 

Agree, Dave.  But let’s not forget that the original topic of this thread was how to combat EMI.  Any recommendation on reduction in sensitivity setting (at least on my part) was solely focused on mitigating EMI, not ground noise (I have edited my my prior post to ensure that was clear).  Agree that lowering sensitivity in mineralized ground or black sand without EMI present accomplishes nothing.  However, lowering transmit power can help reduce reflected near field noise off black sand/surface mineralization - to compensate for this, increasing sensitivity is required to balance out the resulting loss of target signal strength provided any present EMI noise can be managed as well.  Even if transmit power is fixed, then reducing sensitivity to reduce ground noise (not EMI) is likely counterproductive.

Bottom line: Getting your detector set up optimally under challenging noise conditions (both EMI and ground feedback) means understanding how your settings affect all these competing factors impact your target signal and the degree of received noise.  Mastering the ability to balance these competing effects by making useful adjustments (in the right order and direction) to transmit power, sensitivity, discrimination and related filters, ground balance, recovery speed, and operating frequency requires some basic general knowledge as well as trial and error in the field.  There are few magic bullets or “catch all” default settings that work for the infinite combinations of variables in these situations, the best you can do is balance the trade offs.