What primarily affects recommended sensitivity

[lomoch]

Been a while since I've been on these forums.
Running my CTX in our favorite site, the machine adjusts the recommended sensitivity low...~8-13. I'm trying to figure out if this is to mineralized ground, EMI, or what.
Site is neighborhood home, plenty of power lines but typical for an old neighborhood. Ground is not necessarily red, but brown and lots of rocks.
When run in auto, or even manual in conservative settings, the machine runs quietly.
Was hoping you guys could tell me what primarily affects the sens on this unit. If I knew confidently it was the soil/minerals, I explore either BBS or PI, but if it's mainly EMI that's telling the machine to run in low, that's good to know as well!

Is there anything I can do with the machine to narrow down what would cause this?...some method that would point one way or another to help answer why?

Appreciate the thoughts/education.

 

[MI-AuAg]

When starting out in a detecting session, doing the "noise cancel" sets the machine to the quietest channel in terms of ambient EMI, from electrical interference sources.

The machine sets sensitivity based on ground phase, so it can basically ignore any ground mineralization in that area, that would otherwise give a false positive, reading the ground mineralization as a target. Some choose to run manual sensitivity, a little hotter than the recommended setting, in seeking a bit more depth. Some choose to run auto. In auto the ground phase is continually monitored and the machine adjusts to those conditions.

I have found the CTX to be the smoothest operating machine I have ever used, without question.

 

[bklein]

Try manually setting NC to 1,6, 11 and record the auto sense for each. Also set a test target 6" or so and check how the settings affect detection.
May be better to live with EMI and use high settings to get the targets.

 

[trojdor]

Running my CTX in our favorite site, the machine adjusts the recommended sensitivity low...~8-13. I'm trying to figure out if this is to mineralized ground, EMI, or what.
When run in auto, or even manual in conservative settings, the machine runs quietly.
Was hoping you guys could tell me what primarily affects the sens on this unit. If I knew confidently it was the soil/minerals, I explore either BBS or PI, but if it's mainly EMI that's telling the machine to run in low, that's good to know as well!

Is there anything I can do with the machine to narrow down what would cause this?...some method that would point one way or another to help answer why?

Appreciate the thoughts/education.

1. It's mostly the ground.
and
2. There's not much you can do about it, other than PI.
(I realize on Dankowski's the flavor of the month is BBS, but if your ground is that bad...skip directly ahead to PI.)

The sens levels really don't look at emi. That's what noise cancel does.
And the ground signal/noise to target signal ratio is the biggest limiting factor on a VLF detector.

Ground conditions can be bad because of high mineralization and/or salinity. Sometimes, really bad mineralization can also have high salinity...a knockout one, two punch.

If you try to compensate and run at too high of a manual sens setting, you'll miss faint signals hidden in the noise 'floor'.

I've found it best to tame the noise, and learn to listen for the subtle, faintest 'hints' of targets.
However, if (as you say) your machine is running quietly at the auto settings, you might try cranking it up till it gets 'nervous'...and see what happens.

Gool Luck,

mike

 

[lomoch]

Huge thanks to all. Mike? Thought that might be you. Appreciate both responses...in both forums!!
Yes...was hoping it was one or the other...ground or EMI. I guess ground is mineralized in some fashion....know we're leaving targets.
As much as I want to try the PI, hat to think of what that yard would look like after trying with all the nails and junk!
And yes, you are right...started to get excited about the whole Sov discussion.

Randy

 

[trojdor]

 

[Bryan V]

A lot of the ground I hunt in is similar to yours, recommending single digits to high teens at best.
If you want the deeper coins you need to run in manual sensitivity in the low to mid 20s.
You will get some noise and false signals but with practice you can learn to hunt with the noisy detector.
I try to run at 23 or better but never below 20. My CTX loses 2 or more inches when I run less than 20.
Visual ID can get REAL jumpy at the upper sensitivity levels in bad ground so I hunt by sound.
If I need to check a signal sometimes I will drop back to Auto +3 to get a good VID on the target.

It took me awhile to work up to the higher manual levels and I'm still working on it.
I run with an open screen but I might start introducing some discrimination to help with the falsing which can get pretty bad in mineralized ground.

 

[Rex123]

Read this post with interest, as I've just come off a field/site that is the most contaminated I've got. I'm in the UK and this site has regularly been flooded, it had a blacksmiths workshop on it for over 100 years, so you can imagine the color of some of the soil from ash etc, iron nails and slag.

I haven't had the CTX long and I've had enough of the false information it gives me, so I went back to basics.

1. full reset

2. coin mode selected pattern 2

3. SUGGESTED sensitivity was 13/14

4. DROPPED it to 7 yes 7 this was a little trick I learnt from the XS

5. covered the screen and just listened.

6. up popped the little mount from 4 inches, nice clear low tone..... the thing is when I upped the sensitivity to recommended I got a null, due to what? I repeated this with a further 4 targets all with the same result.

Have converted image to black and white, metal is pewter, and measures 12mm x 10mm and almost as thin as foil.