Emi Vs Smf

[HardPack]

Recently detected a ferrous rich old mining site for coins & relics using the Minelab EQX 900 experimenting with Park 1 in multi-frequency with factory settings except All Tunes and Iron Bias 2. A road crew was working within a 1/4 of a mile. The detector was definitely picking up EMI from the flagmen radio traffic. There is also an electrical power plant 4 miles line of sight to the north, an overhead high voltage electrical line 12 miles line of sight to the east and a mountaintop microwave station 14 miles line of sight to the northwest. Performed multiple frequency scans and adjusted the sensitivity down to 15 and below, neither reduced the EMI noise level. Five hours later the road crew departed but the EMI grew even stronger. (The power plant gearing up as folks return home from work?) The racket from the EMI was both tiring and annoying but I was able to separate out non-ferrous targets. I have detected this area for years with several single frequency & selectable frequency VLF detectors ranging from 15kHz to 54 KHz plus pulse induction detectors. I have never experienced this level of EMI in this area. I have been using Park 1 and Field 1 in an attempt to pull out deeper high conductors on heavy ferrous trash sites. Apparently that is a no go with SMF in either of these two search modes. The mining site is blanketed with ferrous trash, gold 1 & 2 would require a dig all approach without discrimination. It appears at this point the only option is  Park 2 and Field 2 in either multi or single frequency. Has anyone else experienced this EMI problem with a SMF detector?
 

[Valens Legacy]

I recently got back to Illinois and found more EMI than there used to be when I went to an area I have hunted before.

I turned off the bluetooth  on my 800 and it did help a lot, I really can't understand why but you may want to try it.

I do know that power lines for homes and buildings are now using smart meters and the power companies are placing wifi units about 3/4 mile apart from each other. Most of them are a square box with an antenna on the bottom side, or a square box with 2 antennas on top of it.

Good luck.

[Digalicious]

5 hours ago, HardPack said:

 Has anyone else experienced this EMI problem with a SMF detector?
 

I started using SMF detectors about 2 years ago. I was taken aback at how suspectable SMF is to EMI, compared to SF. For example, in high EMI, any SMF mode would produce massive noise, accompanied by a constantly fluctuating TID. Yet, I switch to a SF mode, and the detector is dead quiet. 

With SMF transmitting and receiving multiple frequencies, it's considered "broadband". As such, it's much more of an open door to EMI. But, I think it goes beyond that. For example, if I'm at a high EMI site, the detector is very noisy regardless of whether I use a low or high weighted SMF mode. If I use a high weighted SMF mode that is weighted around 30 to 40 khz, the noise is massive, yet if I switch to 20 or 40 khz, the noise is completely gone. I would think that the EMI noise level should be similar in a high weighted SMF mode, compared to 20 or 40 khz, but the noise level difference is night and day. That leads me to believe that SMF's eye opening susceptibility to EMI, is more complicated than "broadband vs narrowband"

 

[HardPack]

5 hours ago, Valens Legacy said:

turned off the bluetooth on my 800 and it did help a lot, I really can't understand why but you may want to try it.

I do know that power lines for homes and buildings are now using smart meters and the power companies are placing wifi units about 3/4 mile apart from each other. Most of them are a square box with an antenna on the bottom side, or a square box with 2 antennas on top of it.

Thankfully I wasn’t using the wireless headphones. The nearest ranch houses are half mile to the south and 4 miles over a ridge to the south. There are no buried utilities or overhead power line passing near the site. Vehicle traffic is light so I assume the cell phone signals would be intermediate. The stream channel vertical slate banks served as an EMI echo chamber. Perhaps there is a new unknown cell tower nearby?

4 hours ago, Digalicious said:

in high EMI, any SMF mode would produce massive noise, accompanied by a constantly fluctuating TID. Yet, I switch to a SF mode, and the detector is dead quiet. 

With SMF transmitting and receiving multiple frequencies, it's considered "broadband". As such, it's much more of an open door to EMI. But, I think it goes beyond that. For example, if I'm at a high EMI site, the detector is very noisy regardless of whether I use a low or high weighted SMF mode. If I use a high weighted SMF mode that is weighted around 30 to 40 khz, the noise is massive

On this specific site switching to a desired single frequency may be the only option. Ground balancing over the site ferrous trash presents its own unique problem of just finding a clean area to pump the coil. When a high tone is heard switching to “all metal” to check for ferrous then narrowing the coil sweep over the non-ferrous target works. I am thinking of switching to “ground tracking”, keep multi-frequency, switching to a single frequency and “all metals” as needed. If that fails a remote move inland may be in store for this SMF detector.

Thanks for the insight

 

[Digalicious]

HardPack,

When the coil is sweeping on the ground, the EMI noise shouldn't be heard. Targets should still be able to come through ok.

 

[Chase Goldman]

If SMF EMI is unbearable after you have tried all the usual remedies in order of preference:  Noise Cancel, lowering sensitivity, or selecting a low frequency weighted SMF mode (Park 1, Field 1, or Beach 1/2), then you can try some Hail Marys like increasing recovery speed, switching to fewer tones (stay away from All Tones or dPitch), or notching out the prevelant target IDs that are affected by the EMI, if possible.  Note that ground tracking and ground balancing will only affect ground noise and should have no affect on EMI noise, though EMI should be usually be less evident if your coil is near the ground (unless the EMI is coming from a nearby buried line).  If all that fails in SMF, then go to single (note that when going to single frequency in Park or Field modes, it doesn’t really matter at that point what mode you are in as the mode designation only determines the default disc, tone, and reactivity settings, beach is SMF only, and Gold is 20 or 40 kHz single frequency only which, in general, are not ideal EMI resistant frequencies, though I have encountered odd EMI situations where the higher single frequencies are more quiet than the lowe single frequencies).  When in SF, then take the EMI mitigations listed above in order of preference except substitute lower frequency for lower frequency weighted SMF mode.  HTH

[HardPack]

4 hours ago, Digalicious said:

When the coil is sweeping on the ground, the EMI noise shouldn't be heard.

1 hour ago, Chase Goldman said:

…switching to fewer tones (stay away from All Tones or dPitch)

Okay, took some notes. For now changed Park & Field search modes from All Tones to five tones. A storm is moving in so it will be a few days before I can get back out to the site. Thanks 

[UT Dave]

4 hours ago, Chase Goldman said:

...and Gold is 20 or 40 kHz single frequency only which, in general, are not ideal EMI resistant frequencies, though I have encountered odd EMI situations where the higher single frequencies are more quiet than the lowe single frequencies). 

That's interesting Chase.  The urban EMI in my area, with my Nox 800, for the most part, none of the lower SF's were any quieter than SMF.  Almost invariably ended up in 20kHz when EMI was bad.

Thankfully, I've not had to resort to SF at all since getting the Manticore.  I've been able to run it in SMF even in places I totally avoided with the 800.  Albeit, lowered sens, but have not had a situation yet where I felt compelled to abandon SMF with it.  Whereas, in many places, SF was a given with the Nox.

- Dave

[Digalicious]

16 minutes ago, UT Dave said:

That's interesting Chase.  The urban EMI in my area, with my Nox 800, for the most part, none of the lower SF's were any quieter than SMF.  Almost invariably ended up in 20kHz when EMI was bad.

 

It's interesting to me as well.

In all my urban sites, the higher the SF, the more EMI mitigation I get. 

[HardPack]

Want to get this out there:

The sites I am attempting to detect with a SMF metal detector have several conditions in common: old gold mining camps; located within the Melones Fault Zone (California Mother Lode) and the eastern gold belt; are carpeted with ferrous trash; loads of non-ferrous trash; coins, tokens & gold are all in short supply requiring a lot of effort to uncover.

Today the Melones fault plus the Feather and Yuba watersheds have become the home for water storage reservoirs, electrical generation stations and overhead high voltage transmission lines. These power station are not only located at the lower elevation dam sites but also near higher elevation reservoirs. Many of these power plants control rooms have converts from analog to digital. Microwave signals are often transmitted between a central control room to these remote power stations. Adding to this are the mountain top cell phone towers with G4 & G5 resulting in an abundance of Electro Magnetic Interference (EMI).

In order to deal with these site conditions and especially the EMI, I wanted to have some rough Idea of what the Minelab Equinox was transmitting into the ground. I recalled an older forum post (“What’s the Difference” comparing the ML EQX 800 to Nokta Legend, Dec. 30, 2021).

In that post PimentoUK provided the following information:

“…The Equinox simultaneously transmits 7.8 kHz, 18.2 kHz and 39 kHz in Park1/2 , Field1/2 , Gold1/2 modes, this is an easily observable fact.
My personal opinion is that:
Park1 and Field1 place the emphasis on the 7.8 kHz, and use the other two freqs to help reduce ground signal.
Park2 and Field2 place the emphasis on the 18.2 kHz, and use the other two freqs to help reduce ground signal.
Gold1/2 place the emphasis on the 18.2 kHz and 39 kHz , using the 7.8 kHz to reduce ground signal. The difference between the two gold modes is something I could only speculate about….
There was follow up discussions on the “return signal analysis”.

Prior to the VLF SMF detector the problem was using a VLF single frequency near iron rich ground. VLF detectors offer a discrimination feature Pulse Induction detectors do not. In the iron rich gold bearing regions EMI has added another problem especially for VLF SMF detectors. Other than switching the SMF detector to a single frequency, is there a real solution?