combating surface foil with a negative threshold

[scoopjohnb]

Just a thought on small surface foil and the X-terra 705.

Several of my beaches have these beach cleaning machines pulled behind tractors and although they do a great job.
Well they do have their negative effects towards detecting.
Small jewelry chains get ripped and foil gets eaten and shredded into freakishly small bits.
Usually the wind will lift it and send it to the other side of the beach, but it always ends up here or there.

I've read the E-book regarding the X-terra.
It states that a slightly negative threshold will counter small surface finds.

But I do have this niggling thought in the back of my head.
Would a slightly negative threshold not also be a negative towards finds at depth??

So you are actually "selecting" or "zooming in on" a detection depth ranging from:
A) somewhat below the surface
to
B) somewhat above maximum detection depth

Any thoughts on the matter are very welcome.

 

[DirtAngler]

I was under the impression that a slight negative ground balance setting can increase depth. Will see what others say.

 

[Old Longhair]

I didn't read anything in the book about beating shreaded foil. Offsetting the GB Tracking can help over-neutralize ground minerals and sharpen the responce of deeper targets,,but I don't think that it can compensate for foil covered ground.

 

[scoopjohnb]

I don't know if we are talking about the same thing.

Don't want to mess with the GB yet, just the threshold hum in the headphones.
Dipping it slightly below audible, hence the volume of a very small surface target or deep target would need to push up the volume slightly to be audible.

 

[Old Longhair]

I'm sorry. I did mis-understand your first post.

Randy does say in the book that a friend of his does what you're talking about. He runs a "slightly" negative threshold, and says that it acts as a "surface blanker" against foil and hot rocks. He also warns that you will likely miss small pieces of jewelry and chains.

 

[Digger]

The manual states that having a Threshold set to a negative value can result in small targets not producing a target response big enough to go above the threshold of audibility. They also say that having the Threshold at zero will disable the Threshold, allowing only for the audio response of targets. And they also say that having your Threshold too high can mask the audio response of small targets. Those suggestions were reiterated in my eBook. I typically set mine so that it is just barely audible. I want the Threshold to be "soft enough" so that it isn't distracting. And, I want to hear a Threshold as it tells me (through nulling) when the coil has passed over a target who's value has been set as rejected. (target blanking). With that said, a few years ago, my brother and I were hunting an old site that had produced a few nice old coins over the years. We both had our X-70's and both were using the 6-inch DD coils. I hit a target that gave a sharp TID 24, and pulled out a 3-cent silver. I tossed it back on the ground, kicked a little dirt over it, and told my brother to come over and see what he thought. (one of those detecting "games" we've played for over 40 years) He swept over the spot and couldn't get a thing. I swept over it and it rang out loud and clear. He tried it again.... nothing. We checked all our settings...... same discrimination levels, same ground balance, same Sensitivity, same Auto NC number (after I shut off my X-70), same sweep speed etc. We were even using the same make and model of headphones, with the volumes turned to the max. The ONLY difference between how he had his set up and mine was the Threshold. If I recall, mine was at 7 and his was at 14. We lowered his to where mine was, confirmed he could hear it, and he reswept the area. Walla! He hit the 3-cent silver clear as a bell. So that is when I became totally convinced that having too high of threshold was detrimental to the hunt.

HOWEVER, I've not been able to duplicate those results with any test procedures. In fact, when I listen to the audio response of the Threshold compared to a target signal, they are two totally different sounds. When you sweep over an accepted target, the Threshold goes goes away for a split second, before the audio response from the coin "kicks in". You have to listen carefully because it is very quick. But it is there. The Threshold will go away just as the coin tone comes in. Then, as the coin tone leaves the field of detection, the Threshold resumes. Two entirely different tones from two entirely different sources.

I'd encourage you to try this exercise at home.......Auto NC the detector, set the Sensitivity to the max, All metal mode, turn the Volume up to 30 and set the Threshold to a level that is barely audible. Now, sweep a small coin under the coil. Take a measurement of how far away you can hear the coin, before it is out of range. Leaving all other settings as they were, set the Threshold to minus 5. Repeat the tests and see if you find any difference in how far away you can hear the coin, compared to the barely audible threshold tone. Then do the test again using the maximum Threshold setting. I know, the sound of the max Threshold is way too loud to want to hunt that way, but try the test with the coin and see if you have any difference in "depth". After the experience we had with that 3-cent silver, I know I was very surprised with my results. I won't share them at this time as I would like to hear "other reports". But I was very surprised. Any takers??? HH Randy

 

[T.A.L.LasVegas]

I will run this excersise with my 705 6" HF coil and post me results, I will try and do this tomorrow
Thank you for the project Randy!

HH
Todd

 

[DirtAngler]

Randy,
Will this work indoors? I tried it using a clad dime and the 6" HF DD coil but indoors so no ground balance used. Doing it this way using -5, 7, and 25 threshold settings, my results were as follows: -5 threshold - faint but clear audio at 8 in.
7 threshold - faint but clear audio at 8.5 in.
25 threshold - faint but clear audio at 8.5 in.
Used a fairly fast sweep speed.

 

[Digger]

Your results mirror mine in that there seems to be very little "detectability" difference, with various Threshold volumes. Now you know why that silver 3-cent find has me scratching my head. Had I not witnessed it in person and compared all those settings, I'd have been sceptical myself! Thanks for helping out. I appreciate it.

By the way, did you hear the two totally different tones and the "break" in between them? HH Randy

 

[scoopjohnb]

Thanks for all the info.

I need to do the threshold test, but if I understand it correctly. The threshold on the X-terra 705 is designed to be an alert to discriminated targets, at very much any setting you choose to set it.

Haven't noticed it dropping away just before a target is reported. But the 705 does BEEP at you, whereas some of my other detectors let you feel up a target in the audio response.
In order to get an idea about the target size and shape, I usually flick it into prospecting mode and feel up the target with a slow sweep.

Again thanks for the info, .... it seems my surface foil idea will need further investigation.
I'm on the prowl for small jewelry, so need to be care full I don't mess things up in the settings.

 

[Old Longhair]

In fact, when I listen to the audio response of the Threshold compared to a target signal, they are two totally different sounds. When you sweep over an accepted target, the Threshold goes goes away for a split second, before the audio response from the coin "kicks in". You have to listen carefully because it is very quick. But it is there. The Threshold will go away just as the coin tone comes in. Then, as the coin tone leaves the field of detection, the Threshold resumes. Two entirely different tones from two entirely different sources.

I've heard exactly what you're talking about. There is a distinct threshold break when a target is reported.

When running in Disc rather than the usual AM, I pay peticular attention to the null, and especially when working around trash. I trace the null perimeter looking for good targets. Repeatability becomes a necessary component when tracing disc'd objects, as they tend to be one way hits. Then pinpointing either verifies a good target, or confirms a bad one,
I've also noticed that a lot of false high tones occur when the coil changes direction over a nulled piece.

 

[Digger]

n/t

 

[scoopjohnb]

Needed a set of those earbuds and carefull listening.
Yep, the threshold dips a fraction of a second before a target tone is reported.