Sensitivity Level Compared To Depth

[Digalicious]

Hello.

I did an air test to give me an idea of how much depth is lost when the sensitivity has to be reduced due to EMI or other factors. Although depending on the ground conditions, a SF can be used to mitigate EMI.

I used the 6” coil, a silver dime, M3, and the default of 5 for the recovery speed.

30-10”
29-9.5”
28-9.5”
27-9.5”
26-9”
25-9”
24-9”
23-8.5”
22-8”
21-7.5”
20-7”
19-7”
18-6.5”
17=6.5”
16-6”

 

[oldcoinhunter]

Maybe should try on M1, M2, and single frequencies just to see the difference.

[Digalicious]

Hi oldcoinhunter.

Dropping the sensitivity level in any frequency mode, will produce the same depth percentage loss 🙂



 

[schoolofhardNox]

7 hours ago, Digalicious said:

Hello.

I did an air test to give me an idea of how much depth is lost when the sensitivity has to be reduced due to EMI or other factors. Although depending on the ground conditions, a SF can be used to mitigate EMI.

I used the 6” coil, a silver dime, M3, and the default of 5 for the recovery speed.

30-10”
29-9.5”
28-9.5”
27-9.5”
26-9”
25-9”
24-9”
23-8.5”
22-8”
21-7.5”
20-7”
19-7”
18-6.5”
17=6.5”
16-6”

 

Interesting. Just goes to show you that increasing from sens at 23 to 26 doesn't gain you anything but noise. Even running it at 30 only gains you 1". So it's really best to know what your acceptable lowest number for sensitivity is.  On that chart 24 seems good if you can maintain it. Dropping sensitivity seems to have a greater adverse effect than raising it. 24 - 30 (6 steps up) gains you 1" -  dropping it from 24  to 18 (6 steps down) loses you 2 1/2" . Lesson is -  don't drop sensitivity too much or you lose out, and don't put too much faith in raising sensitivity - it doesn't gain you much at all. Thanks for doing the chart.

[Digalicious]

You're welcome.

There is one site I have that has giant high voltage "power towers". The only way I'm able to use my Vanquish 540 or Legend there, is to significantly drop the sensitivity. On the Legend, the EMi wasn't mitigated until I lowered the sensitivity to about 20. 4 khz and 10 khz were still noisy. It wasn't until 15 khz before the EMI really quieted down. I chose to use 15 khz with max sensitivity instead of SMF with 20 on the sensitivity and a 3" depth loss.

[Jeff McClendon]

That was an interesting test. Thanks for doing it and for giving me something else to do on a cold day.

My air test results were slightly different and a little more incrementally predictable which is what I would expect from Nokta Engineering.

I used a clad US dime, clad US quarter and US nickel in Park M1, M2 and M3. My coins are glued to what amount to medical tongue depressors so I didn't have to worry about keeping my fingers perfectly aligned and I could see the coin clearly at the end of the tongue depressor. I kept the swing roughly the same length, the same speed and at the same height near the center of the 6" coil. I was listening for when the coin stopped giving an audible beep on each left and right pass across the center of the coil. Recovery speed was 5, the frequency scan for each mode ended up being 3 and I used 6 tones.

It turned out that reducing the sensitivity by two digits starting from 30 down to 15 resulted in approximately 1/2 inch of distance lost for each coin. So for instance in Park M3 at sensitivity 30 and 29 the clad dime result was 10", quarter was 11" and the nickel was 11". Park M3 at sensitivity 28 and 27 the clad dime was 9.5", clad quarter was 10.5" and the nickel was 10.5". This pattern was continued all the way down to where I stopped at 16/15 where the dime was 6.5", quarter was 7.5" and the nickel was 7.5". With the two sensitivity setting pairs, there might have been a 1/8th inch difference just beyond or short of the recorded distance for each coin but I just kept it simple. There were eight roughly 1/2" changes in air test results between sensitivity 30 and sensitivity 15 for each coin.

The Park M2 results with the same settings had roughly the same 1/2 inch change per 2 increments of sensitivity. At 30/29 sensitivity the clad dime was 10.5", the quarter was 11.5" and the nickel was 12". At 15/16 sensitivity the clad dime was 7", the clad quarter was 8" and the nickel was 8.5".

The Park M1 results had roughly the same 1/2" change per 2 increments of sensitivity too. At 30/29 sensitivity the clad dime was 11", the quarter was 12" and the nickel was 12". At 16/15 sensitivity the clad dime was 7.5", the quarter was 8.5" and the nickel was 8.5".

[Digalicious]

Hi Jeff.

I made it a point to be as consistent as possible as you described. Regardless, both our test results are similar enough to arrive at a similar conclusion.

Curious though. Why bother with different frequency modes and types of targets, because neither of which should be relevant with this type of test.

...unless I'm missing the obvious?

[Jeff McClendon]

21 hours ago, Digalicious said:

Hi Jeff.

I made it a point to be as consistent as possible as you described. Regardless, both our test results are similar enough to arrive at a similar conclusion.

Curious though. Why bother with different frequency modes and types of targets, because neither of which should be relevant with this type of test.

...unless I'm missing the obvious?

I don’t assume anything. So I didn’t assume that the same targets would have the same results in different frequency modes considering their different sizes, densities and conductivity.  The 3.5” difference between the maximum and minimum setting and the approximately 1/2" increments were consistent. The actual air tests distances were not.

So, I like to do some testing and I like to be thorough and double check everything and assume nothing.

[Digalicious]

I normally don't assume much of anything either. However, the target characteristics and frequencies have no bearing on the percentage of depth loss when reducing the receivers gain.

 

[JCR]

I have noticed that M3 & the single frequency choices hit a target with a slightly softer response than M1 or M2 at the same settings. I have always wondered about why this is.