SP24 coil and air test depth

[mts]

So I just got the new SP24 coil and was doing air tests against the stock coil. At full sensitivity on both coils, I am seeing about a 2" decrease in air test depth with the new SP24 coil. I don't know how this will end up translating out in the real world and we all know that air tests aren't a good indication of real world results.

The new coil does seem a bit quieter so perhaps some people will be able to run their Simplex at full sensitivity where they couldn't before. This could help equalize the depth results for them for the two coils. Perhaps the SP24 at full sensitivity is about as deep as the stock coil at one level down in sensitivity. I tend to run my stock coil all the way up anyway so we'll have to see what kind of results I get.

It is to be expected. Smaller coils almost always give you less depth. But I had read quite a few reviews and watched a few videos from people who said they noticed no reduction of depth with the new coil so I was hopeful that I wouldn't see any reduction either.

I still have to test it out in the real world. If the weather ever improves and I get the chance to get out detecting again I'll do some better testing and give an update.

 

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[Richard Guy]

Have you tested Park1 with v2.77, full blast?

 

[mts]

Have you tested Park1 with v2.77, full blast?

Yes. Park1, v2.77, max sensitivity. That is what I always use out in the field and what I did my test with. It was a very noticeable difference between the depths of the two coils. About 2 inches less on every target with the SP24. Again, this was just in air testing but it was pretty easy to recognize the difference.

 

[mts]

I'll add a little more info about my results. First off, air tests are funny things and people tend to let their desire to prove a machine's depth run wild with them and skew the results. You see people on youtube swinging a quarter past a detector chattering like a mad squirrel and declare that it can detect the quarter at 16 inches! Well, not in such a way that you would ever stop and dig that signal in the real world. But that is another topic.

So for me, my test was specifically designed to test the difference between two different coils. And I wanted it to be a reasonable real world test. So as you pass the target over the coil, there are two output scenarios that are easy to recognize and thus compare.

#1 - The first one is the point where you stop getting a VDI number and depth reading completely but you still get some sort of beep. I consider this to be the maximum depth of the machine but you may not be able to recognize it in the real world. I chose not to use this technique because it is a little harder to get repeatable results.

#2 - The second technique is where the detector still shows a VDI number, but the depth indicator just goes blank. This is usually about 2 inches shallower than the technique discussed in #1 above. At this point the detector can't really determine depth because it is not getting enough of a response back but it still has enough of a signal to guess at a target ID. TID will bounce around a bit but it is still a recognizable signal and you would dig it knowing that it is really deep and thus something potentially really old. I was also receiving more consistent and repeatable measurements using this technique which made a direct comparison of coils more valid.

So I used technique #2. Here are my results. Keep in mind that with all the depths listed here, the true maximum depth (still get a beep but no target ID or depth indicator - ie - technique #1 above) is probably up to 2" deeper. All depths are to within half an inch.

Stock Coil: (results listed as "Target Type - Depth - TID")
Zinc Cent - 9" - 67
Copper Cent - 8.5" - 78/79
Nickel - 10" - 24/25
Clad Dime - 8" - 77/78
Clad Quarter - 10" - 90/91
Silver Dime - 8" - 85/86
Silver Quarter - 10" - 93/94
Silver Half - 11" - 95/96
14k Gold Ring - 10" - 52/53

SP24 Coil: (results listed as "Target Type - Depth - TID")
Zinc Cent - 7" - 67
Copper Cent - 6.5" - 79
Nickel - 8" - 30/31
Clad Dime - 6.5" - 78
Clad Quarter - 7" - 90/91
Silver Dime - 6" - 85
Silver Quarter - 7" - 92
Silver Half - 8" - 95
14k Gold Ring - 7" - 55/56

So most targets were about 2" less with the quarters both being 3" less. Not sure why that is and could just be my testing technique which is not exact. But it was very easy for me to tell that I was just not getting as much depth out of the SP24 coil. Also, as others have noted before, the TID numbers can be a bit different with the new coil, especially on the lower end of the spectrum. Nickels come up 30/31 on the SP24 coil and 24/25 on the stock coil.

And, as stated before, the depths listed here are for air tests and are not really maximum depths. This test is designed to compare two coils and not to determine the maximum depth capability of the machine. Although my SP24 depth value for a silver dime is 6", it may still be possible to detect a silver dime at 8" with this coil. You will only get a beep and no TID or depth reading, but you will still be able to potentially detect it being in the ground. Depending on where you are, digging those signals may give you some great results.

Finally, as I've stated before, depth is not everything in metal detecting. It certainly helps. But the unmasking capabilities of the SP24 coil may result in better finds anyway. Especially in trashy sites. I tend to hunt a lot of trashy streams and river banks where you are usually close to bedrock anyway. I don't need extreme depth there so hopefully the SP24 will be a game changer in those types of environments.

Hope this is helpful. I can't wait for the weather to get warmer so that I can go out and put this theory into practice.

 

[Richard Guy]

I'm seeing a vdi increase in quarter, dime, nickel, pennies, ... especially pennies, both zinc and copper using v2.77, either coil

 

[mts]

Interesting... I definitely see a big difference in the VDI for lower end signals like nickels and rings. But my upper end signals seem to be around the same. Perhaps a single digit increase on pennies and such. Instead of 77 I might be more likely to see a 78. But I never looked at them that closely anyway out in the field. Thanks for the info.

 

[pescadore]

Thank you so much for the information. I ordered my SP24 coil and carbon fiber shaft last night. Now all I need is some waterproof headphones and my package is complete.

 

[mts]

Ran my tests again and got much better results. I have no idea why my results were much poorer last time. Here are the updates. The main thing here is that you can still see that the SP24 coil is about 1.5" to 2" less on depth. Keep in mind that these are not "max depth" numbers. These are numbers for the point where you still get a target ID number but no depth indicator. The detector will detect at least 2" deeper than these numbers but with no target ID and just a beep.

Air test with 2.77, full sensitivity, park 1, stock and SP24 coils. Stock coil is significantly noisier than the SP24 coil.

Stock Coil: (results listed as "Target Type - Depth - TID")
Zinc Cent - 10.5" - 67
Copper Cent - 9.5" - 78/79
Nickel - 10.5" - 24/25
Clad Dime - 9.5" - 77/78
Clad Quarter - 10.5" - 90/91
Silver Dime - 9" - 85/86
Silver Quarter - 10" - 93/94
Silver Half - 11.5" - 95/96
14k Gold Ring - 11" - 52/53

SP24 Coil: (results listed as "Target Type - Depth - TID")
Zinc Cent - 8.5" - 67
Copper Cent - 8" - 79
Nickel - 9" - 30/31
Clad Dime - 8" - 78
Clad Quarter - 8.5" - 90/91
Silver Dime - 8.5" - 85
Silver Quarter - 8.5" - 92
Silver Half - 9.5" - 95
14k Gold Ring - 9.5" - 55/56

 

[pescadore]

Seems odd that the silver dime would do better than the quarter

 

[mts]

Seems odd that the silver dime would do better than the quarter

Nice catch. That was a typo.

Also, all of these values are +/- 0.5". I just can't get that accurate when swinging over a wooden ruler with parallax error. So take them with a grain of salt.

 

[Richard Guy]

Has anyone air tested Park1 and Field settings, SP24 and stock coils with v2.77

 

[Rmeav8r]

I’ll add this to the discussion. I’ve had the SP24, Park 1 and v2.77 for about 6 weeks. Very pleased with it, separation and locating targets are the biggest improvements. Yesterday I went back to an old church yard where the church was demolished a few months ago. I had been hunting there a few times a week and thought I’d switch back to the stock coil and try it...thus was due to the discussion on this thread. First impression with the stock coil, I was totally lost trying to separate targets from trash, pinpoint skills were terrible too. I dug a few coins but had a heck of a time at it. I then found a pretty good target that hit 80-82, it was a weak signal and I couldn’t get a good pinpoint on it to dig. At that point I was flustered with the stock coil and went to my truck and changed it out. I changed to the SP24 balanced it and headed back. The target was gone! Tried Field, Park 1 and 2 full blast and no luck. So I’m think there is a difference in depth, how much I have no idea. I kept the SP24 on and stayed with it but I’ve got the spot marked to return to later. I’m still happy with the SP24 because it’s more productive in the long run.

 

[pescadore]

I’ll add this to the discussion. I’ve had the SP24, Park 1 and v2.77 for about 6 weeks. Very pleased with it, separation and locating targets are the biggest improvements. Yesterday I went back to an old church yard where the church was demolished a few months ago. I had been hunting there a few times a week and thought I’d switch back to the stock coil and try it...thus was due to the discussion on this thread. First impression with the stock coil, I was totally lost trying to separate targets from trash, pinpoint skills were terrible too. I dug a few coins but had a heck of a time at it. I then found a pretty good target that hit 80-82, it was a weak signal and I couldn’t get a good pinpoint on it to dig. At that point I was flustered with the stock coil and went to my truck and changed it out. I changed to the SP24 balanced it and headed back. The target was gone! Tried Field, Park 1 and 2 full blast and no luck. So I’m think there is a difference in depth, how much I have no idea. I kept the SP24 on and stayed with it but I’ve got the spot marked to return to later. I’m still happy with the SP24 because it’s more productive in the long run.

Getting my SP 24 coil today and put my detector back to Ver 2.77 to give it a try. 2.77 seemed to do a little better with the 11" coil than 2.78.

 

[pescadore]

Getting my SP 24 coil today and put my detector back to Ver 2.77 to give it a try. 2.77 seemed to do a little better with the 11" coil than 2.78.

Tested the SP 24 on a 8-9 inch silver dime I have buried in my yard. I used Ver 2.77 first and got a good audible signal but the VDI was very jumpy. I messed around with 2.77 awhile and it seemed a little more unstable and noisy than 2.78. I switched back to 2.78 and tried the dime with very similar results. I prefer 2.78 because it seems a little more stable and quieter. I am running the detector on Park 1 with the Sensitivity all the way up.

 

[Capncrunch]

I'll add a little more info about my results. First off, air tests are funny things and people tend to let their desire to prove a machine's depth run wild with them and skew the results.

So most targets were about 2" less with the quarters both being 3" less. Not sure why that is and could just be my testing technique which is not exact. But it was very easy for me to tell that I was just not getting as much depth out of the SP24 coil. Also, as others have noted before, the TID numbers can be a bit different with the new coil, especially on the lower end of the spectrum. Nickels come up 30/31 on the SP24 coil and 24/25 on the stock coil.

And, as stated before, the depths listed here are for air tests and are not really maximum depths. This test is designed to compare two coils and not to determine the maximum depth capability of the machine. Although my SP24 depth value for a silver dime is 6", it may still be possible to detect a silver dime at 8" with this coil. You will only get a beep and no TID or depth reading, but you will still be able to potentially detect it being in the ground. Depending on where you are, digging those signals may give you some great results.

Finally, as I've stated before, depth is not everything in metal detecting. It certainly helps. But the unmasking capabilities of the SP24 coil may result in better finds anyway. Especially in trashy sites. I tend to hunt a lot of trashy streams and river banks where you are usually close to bedrock anyway. I don't need extreme depth there so hopefully the SP24 will be a game changer in those types of environments.

Hope this is helpful. I can't wait for the weather to get warmer so that I can go out and put this theory into practice.

Excellent information! I'm glad you made an apples to apples comparison, with a very good explanation of your process and specifically designed to show coil-depth differences!
I do want to add (as you may have alluded to) that there is the 'Halo Effect'- where the ground around the metal target actually becomes a portion of the what the detector 'sees' with ALL metals- even coins. It can cause a small target to 'appear' to be a larger target- to the detector. So that, air-testing, while good for depth comparison may vary wildly from actual (in the ground) results, based on the amount of time that the coin has been in the ground. which is actually good for detectorists, since the target MAY be easier to detect, the longer it's in the ground!
And yes, I have been re-hunting trashy sites and finding all kinds of new goodies with the SP-24!

 

[louisianaman]

Park 1 ground balanced will get deeeep with that 24

 

[Capncrunch]

I then found a pretty good target that hit 80-82, it was a weak signal and I couldn’t get a good pinpoint on it to dig. At that point I was flustered with the stock coil and went to my truck and changed it out. I changed to the SP24 balanced it and headed back. The target was gone! Tried Field, Park 1 and 2 full blast and no luck. So I’m think there is a difference in depth, how much I have no idea. I kept the SP24 on and stayed with it but I’ve got the spot marked to return to later. I’m still happy with the SP24 because it’s more productive in the long run.

Did you ever go back and dig the 80-82 target? Just curious if it was a good find?

ALSO: I was detecting a relic site (1850 house) and found this TINY baby ring, at about 5-6"! It said about 14-16 on TDI, BTW. I air tested it and found that the SP24 hit it at about 7" and the SP28 at about 7.5"! Because the site is so old and trashy, it is extremely difficult to hunt with the stock coil (because of chatter, false-signals, and general instability-- I TRIED, to get the extra depth). But the SP24 is quieter, and has found DEEP items (up to 12" on old pocket knives!) and I have began carrying a plastic plate to put all the dirt BELOW my 4-6" plug onto!

 

[Rmeav8r]

I did go back and it was a clad dime. Also some nearby trash that made it harder for me to locate it.

Did you ever go back and dig the 80-82 target? Just curious if it was a good find?

ALSO: I was detecting a relic site (1850 house) and found this TINY baby ring, at about 5-6"! It said about 14-16 on TDI, BTW. I air tested it and found that the SP24 hit it at about 7" and the SP28 at about 7.5"! Because the site is so old and trashy, it is extremely difficult to hunt with the stock coil (because of chatter, false-signals, and general instability-- I TRIED, to get the extra depth). But the SP24 is quieter, and has found DEEP items (up to 12" on old pocket knives!) and I have began carrying a plastic plate to put all the dirt BELOW my 4-6" plug onto!View attachment 1920990

 

[Capncrunch]

Park 1 ground balanced will get deeeep with that 24

Yes it will! I have dug deep coins, knives, etc.
BUT, I have started re-hunting an 1850s site that I had hunted all of, 2-3 times (N-S, E-W, and even some diagonal) with the SP24, and did awesome! IDK if it's because I am now using the SP28 or because I have started doing my 'Simplex Shimmy' (where I swing only partial sweeps, and barely move forward, tightening the swings for any questionable tone until I either dig or eliminate it)- or BOTH. But, I have now found 8 (EIGHT!) silver dimes- ranging from a 1902 to 1943- that I had missed with the SP24!
My last outing, I even dug a .100" X .210" Brass Berdan primer, that was several inches deep!
To be fair, I HAVE tried the SP24 on some of the questionable targets, after locating them with the SP28, and some of them it picked-up too, but some of them it did not!
There is a lot more EMI and extra signals to deal with, but I am finding too much 'new' stuff to ignore the difference. IF I can do it, with the EMI being higher in some areas, I intend to re-hunt the entire (2 acre) yard!
So, I am not sure what to say, I love my SP24, BUT...

 

[Richard Guy]

That shimmy-wiggle pops! slowly raise while wiggling, if the target ID stays, its usually not trash, ... as I dig my 945,000th bottle cap