Reminder: Use Single Frequency to Eliminate EMI with Multifrequency Detectors

[LawrencetheMDer]

I’m currently using a Manticore with M15 coil. Have a particular hunting area where EMI makes hunting extremely difficult and probably missing those subtle targets. Was reminded recently by Andy Sabisch’s book on the Manticore as well as by the Manticore User’s manual; when faced with excessive EMI switching to a single frequency can eliminate EMI. In my case I switched to 40 khz because I was looking for small gold. I was surprised how much of the interference was eliminated (all of it). I know I must have read this before, but being reminded of it when you need it can make all the difference.

Happy Hunting

[F350Platinum]

Good tip and reminder, LTMDer. 🏆

While @Joe D. and I were hunting a particular beach the EMI was extremely strong, so much so that it had to be skipped by us, but there were huge erosion bags there anyway 🤷‍♂️ I wonder now if that would have helped. 🤔 It's all hindsight. 

I do have a Single Frequency program on my Deus 2 that helps sometimes, and turning down Audio Response will also help in extreme situations. Lowering sensitivity will help on the Manticore if ya want to cut EMI too.

[Knomad]

Any multi frequency machine is more prone to EMI simply because there are more frequencies for the EMI to hit.

SO, yes switching to a single frequency will usually eliminate some if not most EMI.

BUT, you do lose the advantages of the multi mode.

What I would like is an option to eliminate one frequency at a time to find what one or ones are picking up the EMI, while keeping the ones that don't.

[Chase Goldman]

1 hour ago, Knomad said:

Any multi frequency machine is more prone to EMI simply because there are more frequencies for the EMI to hit.

It's a lot more complicated than that but you are sort of on the right track.  It has a lot to with how much input filtering is applied to the recived target signal.  With a multifrequency machine the detector receiver has to be able to "see" a wider range of target signal frequencies therefore the input filters have more bandwidth and can see a wider range of possible EMI frequencies too.  Single Frequency mode allows more selective/narrow filters to be used which can filter out a lot of randon EMI frequencies.  The reason why higher detector operating frequencies tend to be quieter is because higher frequencies are attenuated more so you have to be closer to the source of the EMI if you are filtering out everything but 40 khz target signals vs. 4 khz target signals.  Also, EMI can get into the circuits directly through poor shielding of the control box (vice through the coil).  That's typically how your cell phone interferes with your detector.

When combating EMI it's all about trading off the lesser of several evils.  Going to single frquency is a little bit down the list for me for the reasons cited by Knomad, I hate to lose the superior ground handling and target ID that MF brings to the game.

The first thing you should attempt should be obvious to most, redo a noise cancel if you encounter EMI.  If that is ineffective, see if you can get away with a slight lowering of sensitivity.  Sometimes increasing recovery speed can help too.  Obviously, these both affect depth.  So if you find that you are severely handicapping yourself with a significant sensitivity reduction or high recovery speed setting, try a different MF mode (e.g., go from Park to Gold mode).  If all of that proves ineffective, then pull the trigger on single frequency mode and go from low to high to trade off noise vs. the optimal frequency for the primary targets of interest.  If going for small gold or similar targets proceed right to 40 khz or whatever is your max frequency.  If going for high conductors choose the lowest frequency that still cuts the noise to acceptable levels.  That may still mean you're stuck at 40 khz.  In that case you just have to take what you can get.  HTH.

[Salone]

An excellent discussion.

5 hours ago, Chase Goldman said:

When combating EMI it's all about trading off the lesser of several evils.

This states the heart of the matter to my mind. Well said. I use the Legend in high EMI urban areas with good result by using this mindset. Because I am hunting recent drop small jewelry where depth is not the goal, the strategy is more straightforward. My soil is generally mild so using 40 kHz single is a more attractive option than in the more mineralized soil that others have.

For me and what I do, Higher sensitivity with a higher recovery speed is the more desirable, and when EMI is bad single frequency in goldfield mode is very helpful. I do not know detector engineering like you folks, this is just what works for me. Small shallow targets in mild soil do not demand the enhanced ground handling of more mineralized ground but needs the sensitivity and separation to pick these things out of the modern junk. Or so it seems to me.

The one exception to this has been one place near a railway switching yard. To get the legend to run even close to stable there demanded severely reduced settings and I could find no way to get even close to what I consider good detector operation. Those trains and whatever else was in that place was terrible, and I was unable to come up with a good solution for it. Even hunting near the international airport was nothing near as bad, though often it requires considerable fiddling if under an active runway zone.

The small round coil also really helps in my opinion. Being able to hunt in EMI is a real help for me. I so much appreciate these excellent posts.

[UKD2User]

I notice in the OP "...with M15 coil..." followed by "...because I was looking for small gold...".

Of course the M15 can find small gold, but maybe not ideal? Choosing a smaller coil (if available, of course!) would have been my first attempt to mitigate EMI (and to increase the odds of spotting small gold, all else equal) in this case.👍

[Joe D.]

   Going from @LawrencetheMDer picture, I'd say he was using the M15 for coverage; or else trying to speed detect while kite boarding!🤔😜

   I do much the same on my beaches! But, @UKD2User you are correct about the smaller coils helping (some) in EMI mitigation! As @F350Platinum mentioned, we had this same issue recently in a smallish spot we were at! We used the M15, and the M9 on two different days, and while moderately reduced, that spot was still pretty overwhelming! I did not switch my program or frequency though, and should have thought of that! We were preoccupied with dodging frequent slamming waves and rocks, to fiddle much! There was also a ton of iron targets and destroyed house parts (copper, brass, aluminum) intermingled with the good, that didn't help matters much! And the M9 obviously did better at sorting through the trash!🍀👍👍

[LawrencetheMDer]

On the beach small gold means something different than in gold fields with milligram targets.  But given the targets I have found over the past 2 yrs with the Manticore M15, I sure wouldn't want to find anything smaller.  As a matter of fact, my custom program de emphasizes targets with a VID below 9 since measuring over 50 gold rings found that none fell below a VID of 9 (they do occur if broken or sub 1g weight, but rare).  [And in contrast to what is stated in Andy Sabisch's book on the Manticore, gold rings can have a VID greater than 60; these are typically verty large or/and have very high (22, 24) karat weight.]  On well visited (and hunted) beaches it is all about coverage and depth is really secondary.  But using 40 khz, even for a short period of beach hunting, opened my eyes about using more of the potential of the Manticore in varying conditons.  Guess that is why I just bought an M8 coil, but that is for another discussion.

[Knomad]

On 2/18/2026 at 10:04 PM, Chase Goldman said:

t's a lot more complicated than that but you are sort of on the right track.  It has a lot to with how much input filtering is applied to the recived target signal.

True,

But the reality is if the EMI happens to hit smack in the middle of a particular frequency, filtering is just not going to get rid of it nearly as well as just eliminating that frequency.  Like I said, I wish we had the option of eliminating just one or however many frequencies we want, and keep the rest.