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

[Jeff McClendon]

I read it very carefully several times along with your posts.

Instead of using words like seems, apparently, surmised, maybe, in general, possibly, secret sauce, I just turn on my Equinox 800 or Equinox 900 in my house, in front of my wireless streaming flat screen TV, next to my wireless streaming iPad and iPhone 13, directly over my wireless router a floor below, with LED and halogen lights switched on that use rheostats, and I listen to how quiet 4 kHz and 20 kHz and 40 kHz are especially compared to 5 kHz and 10 kHz and to a lesser degree 15 kHz.

Endless argument, speculation and regurgitation of theories and current technology will not eliminate EMI in metal detectors that are acting like broad spectrum antennas. I don't expect EMI elimination when I turn on a metal detector especially one that is using SMF technology. A reduction in EMI interference to where I can effectively detect is good enough for me at this time.

[Steve Herschbach]

First comment - chill out folks. Like seriously take a chill pill. It's just metal detecting. 

Of course just changing base frequency can reduce EMI by shifting away from what caused the EMI. And no, there is not and will not be any magical fix short of basic trade offs. The detector is just a dumb machine and can't tell signal generated from a target by that caused by spurious EMI. Reducing a particular EMI problem can also reduce a certain target signal because they are identical as far as the detector is concerned. The engineers can shift frequencies or use frequency comparison tricks to try and sort this from that, but the bottom line is any filtering always comes at a cost. A trade off where you gain something but lose something else. I'm not just speculating here - I was very involved in working on EMI mitigation with Equinox and it is not ignored at all. The solutions are just not as simple as people think. Well it is I guess. Go back to using a lower gain 1980s detector that will be nice and well behaved. It's the fact we are pushing the tech to the limit and running extremely high gains that are the source of the issue here. The solution is simply turn down the sensitivity until the EMI goes away. Happy?

[Digalicious]

Yes Steve, I'm happy that you are saying what I have been saying all along. Although, my explanations are much more wordy than yours 😉

[GB_Amateur]

20 minutes ago, phrunt said:

FREQUENCY SHIFTING
One disadvantage of a highly sensitive metal detector is its susceptibility to electrical
interference from other electronic devices. If the detector chatters while the search coil is not in
motion, the cause is either electrical interference or internal circuit noise due to a high
sensitivity setting. If the detector chatters or emits intermittent false signals in the field, you are
also probably experiencing electrical interference. If you suspect electrical interference, you
may change the T2’s operating frequency. This is a trial and error method to try to find a
frequency different from the suspected source.

Each actuation will shift the frequency by one value.
The LCD will display the frequency, from F1 to F7. The
default frequency is F4. The T2 will default back to F4 when
the power is switched off

Although the Fisher F75 is a different detector, it has common DNA with the Teknetics T2.  Here is what the F75 manual (black model w/DST) says about the similar frequency adjustments on the F75:

The middle (default) frequency is 12.987 kHz and the increments above starting at this base value are respectively (in kHz units) 0.056, 0.057, 0.058 and going below baseline respectively 0.056, 0.055, 0.055.  Pretty small changes on the scale of things, but apparently (from phrunt's video) sufficient in some EMI situations.

[phrunt]

The frequency shifting would be an awesome feature to have on something like a Nox 900, and something they should have done for it's single frequency modes, how cool would have have been if you could switch to 4khz, then also adjust it in small increments like the T2/F75 to get it fine tuned to the local EMI.  Perhaps this is what the noise cancel tries to do, and you can manually adjust the noise cancel channel.

As Steve said though, get it as good as you can, lower the sensitivity if need be which often it is, or just change to a smaller coil which helps a lot.  There are ways to deal with it.

One thing I've found is you're better off lowering sensitivity to clear up EMI than trying to detect through it, you get better performance with sensitivity and depth by lowering sensitivity than you do trying to fight it.

[Digalicious]

2 minutes ago, phrunt said:

 

As Steve said though, get it as good as you can, lower the sensitivity if need be which often it is, or just change to a smaller coil which helps a lot.  There are ways to deal with it.

I'm glad you mentioned using a smaller coil, because using a smaller coil makes a phenomenal difference with EMI noise. Strap on a stock 11" coil and the EMI is overwhelming. Switch to something like a 9x5, and wow, the silence is deafening (comparatively so lol). Plus, with the 9x5, sensitivity can be run much higher than the round 11", and the added bonus of a 9x5 is superior separation and unmasking ability.

[Chase Goldman]

Dig - none of us can prove or disprove any of this because we didn't design these rigs.  So if you want concrete answers about what's going on under the hood.  Ask the manufacturers directly.  Who knows, maybe they can answer your questions without giving away state secrets.

Those using the Equinox don't really care how ML made 4 khz quieter, they just know from experience it is, they can run higher gains than 5 khz, find decent targets at depth, and are not seeing any noticeable performance hit (even if there is a slight gain reduction).  Simple as that.

[Jeff McClendon]

11 minutes ago, phrunt said:

The frequency shifting would be an awesome feature to have on something like a Nox 900, and something they should have done for it's single frequency modes, how cool would have have been if you could switch to 4khz, then also adjust it in small increments like the T2/F75 to get it fine tuned to the local EMI.  Perhaps this is what the noise cancel tries to do, and you can manually adjust the noise cancel channel.

As Steve said though, get it as good as you can, lower the sensitivity if need be which often it is, or just change to a smaller coil which helps a lot.  There are ways to deal with it.

The Equinox 800 and 900 have 19 different increments within each SMF or selectable single frequency setting that can be automatically or manually shifted. On the 600 (don't know about the 700) automatic small incremental shifting of frequencies was the only option.

[Skyshark]

14 hours ago, Jeff McClendon said:

I really don’t know why 4 kHz is less interfered with here in the USA than 5 kHz. Maybe the 60 Hz USA and 50 Hz difference in the UK and most of Europe and Asia has something to do with it.

Perhaps this a silly question, but if the primary driver from ML was to give users in Asia a "better" frequency for that region, wouldn't we be best to get feedback from someone in Asia or who has used it in Asian soils? Do we have anyone on the forum like that?

Also, I echo the comment about asking manufacturer direct. I sent them an email, we'll see if they respond.

[phrunt]

5 minutes ago, Jeff McClendon said:

The Equinox 800 and 900 have 19 different increments within each SMF or selectable single frequency setting that can be automatically or manually shifted. On the 600 (don't know about the 700) automatic small incremental shifting of frequencies was the only option.

Thanks Jeff, yea I'm not sure if that is switching frequencies or if it was something else the way it's called noise cancelling and channels.  I have no clue how it works but I do know the good old fashion frequency shift works pretty good 🙂