Emi In Relation To Depth

[Digalicious]

Hello everyone.

The following is an air test using the Legend with the 11” coil, all metal, max sensitivity, default recovery speed, on a silver dime and a large diameter 10k gold ring. I tested in my backyard that has what I would call “medium” EMI (3 medium power lines, and 1 low power line). I would consider being near those large power towers as “high” EMI, and out in the country with no power lines near, as “low” EMI. I’ll follow up tonight or tomorrow with the results of the same test in a low EMI area.

Even though I tested using the Legend, I’m thinking the results would be similar with other similar detectors and the same testing methodology.

M1 is mid weighted, M2 is high weighted, and M3 is low weighted.


Silver dime / Gold ring

M1 - 13” / 17”
M2 - 13” / 19”
M3 - 13” / 17”

4 khz - 12” / 14”
20 khz - 13” / 19”
40 khz - 13” / 17”

I’m giving my margin of error as ½” either way, but realistically, there was no “oh wow” air depth difference on the silver dime using any SMF or SF mode. However, there could very well be a depth difference based on the ground mineralization. But, I’m testing EMI in relation to depth, so the air test will suffice for this type of test.

[phrunt]

I wonder why 4kHz was the worst for the silver coin, as I find 4kHz on the Equinox 800 the deepest frequency for silver coins in the ground.

 

[Digalicious]

10 minutes ago, phrunt said:

I wonder why 4kHz was the worst for the silver coin, as I find 4kHz on the Equinox 800 the deepest frequency for silver coins in the ground.

 

Hi phrunt.

A video would have been better, because that way the EMI noise can be heard. There was so much EMI noise in the SMF modes and 4 khz, that it got somewhat hard to determine the target signal from the EMI noise, when the target was far from the coil. In 20 and 40 khz, there was almost no EMI noise to contend with. Then again, when the coil is swinging on the ground, EMI noise diminishes significantly. Plus, if the targets were in the ground, the actual depths could very well be different.

I'm mainly trying to find out if EMI will affect depth, so the air test "should"? be fine to do that. I'm going to that low EMI site tonight, and really looking forward to seeing the results when I duplicate the test there.

 

[Digalicious]

I repeated the experiment in the low EMI site.

On both the silver dime and the large diameter gold ring, there was a 2-3" depth gain in all SMF and SF modes. Thing is though, the depth increase also occurred in the SF modes that had no audible EMI noise in the first mid level EMI test. Does that mean that EMI doesn't have to be audible for it to affect performance?

Further to that, this experiment was comparing the air depth difference between low and mid EMI sites. I wonder how much more depth loss there would be in a high EMI site.

With all that said, the depth loss for in ground targets, probably wouldn't be as significant as this air test. Reason being, EMI is notably reduced when the coil is swinging on the ground.

[Chase Goldman]

On 9/14/2023 at 9:21 AM, Digalicious said:

Does that mean that EMI doesn't have to be audible for it to affect performance?

"Silent EMI" is indeed a thing.  It typically results from inter-detector interference but any near-field EMI source such as a cell phone or other radio transmitter or powerful EM fields from power lines can result in target signal attenuation without an accompanying audible "noise" effect.

[Digalicious]

2 hours ago, Chase Goldman said:

"Silent EMI" is indeed a thing.  It typically results from inter-detector interference but any near-field EMI source such as a cell phone or other radio transmitter or powerful EM fields from power lines can result in target signal attenuation without an accompanying audible "noise" effect.

I wasn't so sure about the silent EMI thing, but I am now.

It's as though the coil's balance gets so "saturated" by the noise, that the target now has to present a notably more powerful signal to overpower that saturation threshold. Is that what you mean by target signal attenuation?

On a side note, we would all prefer to not have to lower the sensitivity any more than necessary, and thankfully, the EMI noise is almost nonexistent when swinging the coil on the ground. However, once the detector is set down to dig, the annoying noise returns. That makes me wonder why detectors don't have a simple mercury switch or gyro, that you can enable or disable, and would mute the detector when it's horizontal. Heck, that feature would save on battery power too. Or, instead of muting the detector, it causes the detector to go into an "instant on sleep mode", which would save even more battery power.

[Chase Goldman]

19 hours ago, Digalicious said:

That makes me wonder why detectors don't have a simple mercury switch or gyro, that you can enable or disable, and would mute the detector when it's horizontal.

Already exists.  The new Quest SMF detectors do have a gyro/accelerometer.  They use it to auto initiate GB (operator just starts pumping the coil) and to put the detector into sleep mode if it is no swing is detected after a preset time period.  I use a set of phone where you can just flip a switch and mute the headphones during recovery.  I thought Nokta had a mute feature so that Pinpointer interference could be muted during target recovery.  Easy issue to address multiple ways.

 

[Digalicious]

The sleep mode on the Quest sounds interesting, provided that the sleep process is initiated immediately upon setting the detector down, and the wake time is instant as well. For the purpose discussed, I'm thinking a simple mercury switch would be better, and it costs almost nothing.

Yes, the Legend and Simplex have a mute feature. For the Legend, the Frequency button is held down to mute, then pressed again to unmute. I'm glad it has that feature, but it's just more damn buttons to push every single time a target is retrieved. I have the same "button pushing for target retrieval " ire for pinpointers. All SMF detectors should have said mercury switch or similar, and all pinpointers should have a magnetic switch holster.

/end old man yelling at clouds rant 😁

[Chase Goldman]

7 hours ago, Digalicious said:

The sleep mode on the Quest sounds interesting, provided that the sleep process is initiated immediately upon setting the detector down

As stated in the screenshot, the Quest initiates sleep mode within 5 seconds of detecting no motion.  Gyro much more versatile and robust than a merc switch. Seriously though, first world problems.  Like I said, I just flip a toggle right on my phones. Or if I'm using my wireless pinpointer, it mutes the detector anyway.  The Quest magic pinpointer holster is also a great little gadget.