What Difference Does 1khz Have On The Equinox From 5khz To 4khz?

[RickUK]

Folks i have had my Nox a for maybe 4 years,i rarely use it if i am honest,but one that i have still not fathomed out yet is what difference does the 1 khz do on the frequencies ??

I am totally aware that lower freq's go deeper and the Nox originally came with the 5khz as the lowest freq and when coupled with the larger 15x12 that would give you greater depth,but when the update was available the lower freq was reduced to 4khz which i installed that update,but still cannot fathom out why or how just 1 khz can make a massive difference or am i missing something here.

As i dont use this detector as a everday machine,i am plan on using it with the 15x12 coil for deeper larger artefacts.

[Dug D]

That 1 khz has a big change in EMI, 4 seems much better than 5 Khz. 🙂

[Digalicious]

1 hour ago, Dug D said:

That 1 khz has a big change in EMI, 4 seems much better than 5 Khz. 🙂

Hmmm.

I'm not understanding how 4 is better than 5. Not just because it's only a 1 khz change, but also because both those frequencies are very low, and in general, the lower the frequency, the more suspectable it is to EMI.

In my area, anything below around 15 khz is very suspectable to EMI, but still much less suspectable than any SMF mode. 20 khz is significantly better, and 40 khz is more or less dead quite, as it's outside the range of EMI. Well, that's been my experience, and up until this point, the experience of every other hunter that I've discussed it with, or read about.

So ya, Dug's post is a surprise to me. Unless I'm missing something, the only way I could see 4 being better than 5, is if the EMI is being emitted by a single strong source at specifically 5 khz.

 

[Chase Goldman]

Minelab introduced 4 khz as a feature "upgrade" a few years after release.  Minelab stated that it was at the request of Asian "horde hunters".  Yes, most were skeptical and scratching their heads regarding the additional frequency given that it was so close to the existing 5 khz setting.  I am pretty sure ML was experimenting with SF noise mitigation, ground handling, and signal processing algorithms as many users noted that 4 khz was incrementally more stable and perhaps had incremental improvements in detection depth on high conductors vs. 5 khz.  In hindsight, it was probably a stealth field test of single frequency enhancements that ML was considering for incorporation into future detectors such as the Manticore, but more likely, this was a test case for enhancements that were eventually incoporated into the X-Terrra Pro.

[Chase Goldman]

34 minutes ago, Digalicious said:

Hmmm.

I'm not understanding how 4 is better than 5. Not just because it's only a 1 khz change, but also because both those frequencies are very low, and in general, the lower the frequency, the more suspectable it is to EMI.

In my area, anything below around 15 khz is very suspectable to EMI, but still much less suspectable than any SMF mode. 20 khz is significantly better, and 40 khz is more or less dead quite, as it's outside the range of EMI. Well, that's been my experience, and up until this point, the experience of every other hunter that I've discussed it with, or read about.

So ya, Dug's post is a surprise to me. Unless I'm missing something, the only way I could see 4 being better than 5, is if the EMI is being emitted by a single strong source at specifically 5 khz.

 

First of all, one needs to be careful about generalizing EMI and the impacts based on operating frequency.  Different detector operating frequencies have different susceptibilities to different EMI sources like 60 hz power line or florescent light balun noise vs. GHz wireless device noise (cell towers, phones, and wifi) and everything else in between.  So its hard to generalize that high frequencies are generally quieter than lower operating frequencies.  There are scenarios that I have encountered that are just the opposite of that.

Also, EMI can interfere with detector operation from several different avenues and can enter the detector from more than just through the coil acting as an antenna.  Operating frequency selection determines how target signals are filtered as they are processed.  But the control box can pick up sources of EMI independent of the operating frequency selected and changing the operating frequency (the typical noise cancellation algorithms) doesn't necessarily fix those issues. 

Regarding the update, ML apparently did something to address EMI and ground handling with the 4 khz "mode" vs. the 5 khz "mode" and it had little to do with the actual operating frequency other than ML probably surmised that if they could make a lower operating frequency mode less susceptible to EMI then whatever they were doing could be used effectively across the board.  Furthermore, they also needed to be concerned about unforeseen consequences such as reduced depth or target sensitivity, hence they left 5 khz alone in the event their "experiment" had unintended consequences.  True, in general there is nothing that makes 4 khz signficantly less susceptible to EMI than 5 khz, but ML must have incorporated some secret sauce to make the added 4 khz mode to be less susceptible or more stable than the existing 5 khz mode.  That extra 4 khz can also make a significant difference on detection depth for large, high conductive targets.

[Digalicious]

14 minutes ago, Chase Goldman said:

  I am pretty sure ML was experimenting with SF noise mitigation, ground handling, and signal processing algorithms as many users noted that 4 khz was incrementally more stable and perhaps had incremental improvements in detection depth on high conductors vs. 5 khz.  In hindsight, it was probably a stealth field test of single frequency enhancements that ML was considering for incorporation into future detectors such as the Manticore, but more likely, this was a test case for enhancements that were eventually incoporated into the X-Terrra Pro.

Thanks for that Chase, because simply going from 4 to 5 should not have any effect on EMI noise. BUT, as you explained, it seems as though 4 is more of an "experimentation" SF, that uses different algorithms than the other SFs. That would explain why some might experience less EMI in 4 khz.

Given past precedence with previous manufacturer's "solutions" to EMI noise, it wouldn't surprise me that if indeed 4 is quieter than 5khz in EMI, then it's a result of dropping the base sensitivity of 4 khz, or some other algorithm that will reduce EMI, but cause a performance hit in another aspect.

EDIT: Oh oh. As I was finishing that last paragraph, I got a notification that Chase posted again 🙂 Let's see...

[Digalicious]

5 minutes ago, Chase Goldman said:

First of all, one needs to be careful about generalizing EMI and the impacts based on operating frequency.  Different detector operating frequencies have different susceptibilities to different EMI sources like 60 hz power line or florescent light balun noise vs. GHz wireless device noise (cell towers, phones, and wifi) and everything else in between.  So its hard to generalize that high frequencies are generally quieter than lower operating frequencies.  There are scenarios that I have encountered that are just the opposite of that.

 

I don't think it's hard to make that generalization, because, by far, that generalization is empirically and experientially true. Granted, there can be exceptions to that general rule, but there are exceptions to just about everything. That's why they're called "generalizations" and not "absolutes".






 

[Chase Goldman]

Without getting into a prolonged back and forth as to whether "...by far, that generalization is empirically and experientially true",  I'll simply link to this excellent thread by Steve that addresses that generalization but also discusses exceptions.  A deeper dive into the thread's technical references and the complex nature of EMI reveals that it's hard to lean too heavily on a single, convenient truism as the variables that affect the outcome of how a detector responds to the vast variety of EMI sources are also numerous. 

Nevertheless, some great nuggets about detector EMI susceptibility and what you can do about beyond sensitivity reductions and frequency shift based noise cancellation routines.

FWIW, I was still curious and asked an expert a general question about metal detector EMI susceptibility and operating frequency and this is what they said about it:

Metal detectors that operate at higher frequencies, typically above 10 kHz, are more susceptible to electromagnetic interference (EMI) than those operating at lower frequencies. This is because higher frequency signals are more prone to interference from other electrical and electronic devices, including power lines, cell phones, radios, and other metal detectors.

At higher frequencies, the metal detector's circuitry and coils are more sensitive to changes in the surrounding electromagnetic field, which can cause false signals and reduce the detector's overall performance. In addition, the higher the operating frequency, the more likely the metal detector is to generate EMI, which can interfere with other electronic devices in the vicinity.

To minimize the effects of electromagnetic interference, metal detector manufacturers often incorporate features such as ground balancing and sensitivity adjustments, as well as shielding to protect the circuitry from outside interference. However, even with these measures, it is still possible for metal detectors operating at higher frequencies to be affected by EMI, particularly in areas with high levels of electromagnetic activity.

That expert...ChatGPT.  🤣

Clears things right up.  SMH

[Digalicious]

Thanks for the Link to Steve Herschbach's thread.

The first thing I noticed was Steve saying:
 

Quote

As a rule, the lower the frequency, the more issues you have with EMI. It is especially bad under 10 kHz. DEUS owners may see significant EMI at 4 kHz, only a little at 8 kHz, and none at 12 and 18 kHz.

That of course has been my experience, and just about every hunter's experience that I've come across. Steve was a little braver than I in saying "As a rule", whereas I was a little more subdued by saying "In general" 😁. I think his "as a rule" was much more accurate than my "In general".

Steve also mentioned that Fisher detector that I couldn't recall the exact model of. It was the F75 in which the EMI noise reduction merely reduced the sensitivity (among other possible dialed down settings) to give the illusion that EMI was being legitimately mitigated. Minelab has previously done the same on one or more of their models. As such, and along with a few other reasons, I don't believe that there is a practical way to truly mitigate EMI without sacrificing performance, nor do I believe that the Manti's long press does anything more than what the F75 and that other Minelab detector did. Although with the Manti, it's also possible that the long press could change the SMF to be ludicrously weighted toward 1 single frequency. That would significantly reduce EMI noise, but also lose the advantages of SMF.

EDIT:

Oh ya. That ChatGPT answer was kind of bonkers lol
 

[Chase Goldman]

Taking the time to read the technical references reveals that the rule or generalization or whatever you want to call is applicable mainly to power line noise sources.   But given the growing proliferation of 5G transmitters and WiFi 6, solid state switching power supplies, and LED lighting, even detectors with higher operating frequencies will be affected more in suburban and even rural areas as time goes on as evidenced by Steve's anecdote about his noisy 19 khz detector.