messin' with my 505, 705 and a few coils.....

[Digger]

Id' be among the first to admit that airtests really don't tell us much about the depth capability of any detector or any coil. But I do think something can be learned by airtests when comparing the same coil on two different dectors. Or, by using different coils on the same detector. I got a little bored last night, so I set up my test bench for my 505 and my 705. I read a US quarter, dime, nickel and wheat penny with four different coils, on each detector. Being indoors, I was not able to ground balance. But I did noise cancel each detector with each coil. Both detectors were running with a barely audible threshold, max sensitivity, multiple tones and in the all metal mode. My airtest simply consisted of measuring the maximum depth that I could hear a repeatable tone, with each detector/coil combination. I did not check the TID as I was simply "hunting by ear" with the two different models, listening for a consistent, repeatable tone. I did not use any headphones, as I never thought of it at the time! I do know there were some audio tones heard "deeper" than the readings I've posted. But not consistent or repeatable. At least not without my headphones.

For this test I used the 9-inch concentric at 7.5 kHz, the 9-inch concentric at 3 kHz, the 6 inch concentric at 7.5 kHz and the 6 inch DD at 18.75 kHz. I used the metric side of a wooden yardstick to provide more accuracy in the measurements. One cm = .39 inch.

(Would you still call it a yard stick, when you use the metric side?)



6-inch concentric at 7.5 kHz
X-505
quarter 21 cm, nickel 18 cm, wheat cent 17 cm, dime 17 cm
X-705
quarter 22 cm, nickel 22 cm, wheat cent 21 cm, dime 20 cm


6-inch DD at 18.75 kHz
X-505
quarter 20 cm, nickel 23 cm, wheat cent 20 cm, dime 18 cm
X-705
quarter 23 cm, nickel 25 cm, wheat cent 20 cm, dime 20 cm

9-inch concentric at 7.5 kHz
X-505
quarter 26 cm, nickel 25 cm, wheat cent 25 cm, dime 24 cm
X-705
quarter 28 cm, nickel 26 cm, wheat cent 27 cm, dime 26 cm

9-inch concentric at 3 kHz
X-505
quarter 27 cm, nickel 20 cm, wheat cent 23 cm, dime 23 cm
X-705
quarter 30 cm, nickel 21 cm, wheat cent 26 cm, dime 26 cm



Again, I don't profess that this has any scientific meaning. Just a few airtests from someone who is tired of snow!!! But if you notice, once again the higher frequency is "deeper" on the lower conductive nickel. And the lower frequency provided more depth on the higher conductive silver and copper. One other thing I noticed is that the 705 has a bit more depth than the 505, regardless of which coil was used. Could be the finer tuning? I don't think so, in this case. Being indoors, I didn't GB, and both detectors were set to max volume and sensitivity with a barely audible threshold. Could be the enhanced software? Could be. But I've not done enough testing to determine anything definitive. Just reporting my findings. JMHO HH Randy

 

[Mick in Dubbo]

I'm shocked Randy. An American using the metric system. Wonders will never cease! For once I won't have to convert the data.
Mick Evans.

 

[Mark in S.E. IA]

I have never cared much for air test, but I like what your trying to do by showing the differences in the coils, with the two MD'ers. It's too bad that you didn't have a 10.5 DD 7.5 kHz coil. It would of been interesting to see how it would of compared with the 9" coils. I'm sure that the 10.5 would of did a little better then the 9" but it would be interesting to know just how much.

One thing that I noticed between the two 9" coils is that over all the 7.5 kHz coil did better then the 3 kHz.

Thanks for doing the test. It was interesting.

 

[Dan-o]

Just curious, were the Quarter and Dime clad or silver?
I wonder if it makes a difference if the they were silver using the 3kHz coil.

Dan

 

[Steve(MS)]

I would be interested in how the 10.5 MF does in the test too, in fact I am looking for a used one somewhere.

 

[Digger]

Actually, I tested both silver and clad coins and couldn't determine any differences. Wear did seem to play a factor on some older coins. But I picked some SL and Bargers that were pretty good shape, and they tested spot on with the newer clad. I am doing quite a few tests at this time, in an effort to prove or disprove some new theories I'm working on. But at this point, it looks to me that if two coins are the same size, shape and have the same TID, they will detect at the same depth. JMHO HH Randy

 

[MXTerer]

n/t

 

[Hawkeye Jim]

Interesting results Randy --- was the quarter and dime silver or clad???

Hawkeye Jim.

 

[Hawkeye Jim]

n/t

 

[Digger]

Like you, I don't give much creedance to air tests, when referencing how well a detector hunts in the field. But I do find that comparing coils on the same detector, or the same coil on two different detectors, does provide some usable information. Since Minelab doesn't make a 10.5-inch concentric, or a 9-inch DD, comparing what they do have available really isn't comparing apples to apples. My 10.5 inch coils are "on loan" at this time. So I didn't add them to this test. Frankly, after having used them for several years, I kept going back to the 9-inch concentric due to the results I got in my moderately mineralized soil. However, if I can pry them away from the guy who has them, I may include them in some "in the dirt" testing when the ground thaws.
As to comparing the different targets using the two 9-inch coils, I suppose which one you prefer will depend on what you are hunting for. True, the 7.5 kHz did have deeper air test results than the 3 kHz on nickels and one cm that wheat penny. But on both silver coins, dimes were equal and quarters were deeper on the 3 kHz. Again, I think that lends credibility to the theories of lower frequencies being better suited for higher conductive targets, higher frequencies being better suited for lower conductive targets, that lower frequencies are better suited for larger targets and higher frequencies are better suited for smaller targets. JMHO HH Randy

 

[Donut]

Great job Randy i think that will help a lot. I wish you would have compared the 5x10 18.75 DD Elliptic and the 10.5 18.75 DD and also , (heck all of the coils on hand (LOL) and air tested the X705 compared to the X70.

 

[Digger]

I have put all the coils through quite an extensive testing process. I could say those test results were the reason I was willing to set some of them aside, and continue using the coils I chose. But with a bit more explanation, I found the 6 X 10 Elliptical to do what it was designed to do (in my opinion). At 18.75 kHz, it is a "longer" version of the 6 inch DD at the same frequency. Frankly, when comparing these two in my moderate soil, I found very little (if any) difference in the depth of detection. There is a little more difference in airtests. But I believe the effects the soil has on the larger "footprint" of the elliptical cancels out any increase in actual hunt depth. They are both DD coils operating at 18.75 kHz. As such, it seems the "width" of the coil is a very important factor when comparing depths. Since both are nearly identical in "width" the main difference I found is in the amount of turf covered with each sweep. Therefore, if I am needing a coil that separates better than the concentrics (which the DD design does), my preference is for the smaller of the two (comparing the elliptical 6 X 10 with the 6-inch DD) simply because the 6-inch round DD does not have to analyze as much soil at any one time. (again, footprint) "Left to right" target separation is nearly equal between these two. But we must consider that adjacent targets are not always to either side of the primary target. Sometimes they are toward the tip or heel of the coil, depending on your direction of sweep. And it those instances, the 6 inch out performs the elliptical. (once again, due to the smaller footprint) As to the round 10.5 DD coils...... since the depth of detection is somewhat dependent on the width of the coil, the "wider" 10.5 round coils will be deeper than an elliptical coil of the same "length". From my observations, the large round DD coils have +/- 40% more depth than the elliptical. I've found the 10.5 DD at 18.75 kHz to be more sensitive than the 10.5 DD at 7.5 kHz. As such, I usually have to lower the sensitivity setting to operate it without falsing. But with all those things considered, both are similar in performance, depth wise. I'm still convinced that I get more "raw depth" out of my 9-inch concentrics than I can either of the two 10.5 inch DD's. But my soil is moderately mineralized, with a typical ground phase reading in the 40's.

There is so much to consider when chosing the proper coil for a particular application. I believe lower frequencies are better suited for higher conductive targets and higher frequencies are better suited for lower conductive targets. I believe that lower frequency coils will detect larger objects at greater depths and higher frequencies are more "sensitive" to smaller targets. I believe that DD coils neutralize the effects of highly mineralized ground much better than concentric coils, making the DD coils a far better choice in those applications. And I believe that larger coils hunt deeper than smaller coils, simply due to the size and shape of the electromagnetic lines of flux being tranmitted into the ground. So when chosing a coil, one must consider the size of targets they are seeking, the mineralization of the ground they are hunting and the amount of "trash" they are likely to encounter. Remember that any of the coils are capable of finding anything metal. It is simply a matter of chosing the best tool for the job. And there are more factors than simply the conductivity of target you are searching for.

I've made many comparisons with my X-70 and X-705. I believe that the software enhancements in the new series of X-Terra has resulted in an increase of detection depth in all models. In the case of the 70 vs the 705, I would estimate that difference as being 10%. During the thousands of hours I spent using the X-70, I dug some pretty deep coins. But the 705 is capable of providing an audio response on some targets that were too deep to signal on the X-70. In one particular "controlled" site (my coin garden), the 705 will produce "whisper" tones on some very deep targets that the X-70 does not respond to. I suppose the question for many would be: is the 705 enough "deeper" than the X-70 to consider a trade-in? My short answer would be probably not. At least not if depth is your only consideration. However, I was interested enough in some of the additional functionality that I bought a 705. Now that I've spent some time with it, I have come to really appreciate several features of the 705 that have made it my "go to" machine. I enjoy being able to offset my tracking GB. I like the sizing pinpoint functionality. And although I never thought I'd use it, the backlight feature is really nice when the sun starts setting and you're not ready to call it a day. The extra depth doesn't hurt my feelings either! JMHO HH Randy

 

[Goes4ever]

I would love to see you do a test between the 9" 7.5 and the 9" 3khz coils over buried coins in a test garden. When I did that I got an EASY extra inch repeatable signal when I used the 3khz VS the 7.5 KHZ on wheats, silver dimes and clad quarters

 

[Digger]

With the 30+ inches of snow we have on the ground now, it will be a few months before I can do some actual "in the dirt" tests. As such, air tests are simply an exercise to keep my mind occupied! However, and I think I may have mentioned this once or twice before, , the 3 kHz concentric coil is a coin killer. Particularly on silver and copper coins, which is about 95% of what I dig. Nickels, gold coins and other low conductive targets...... not quite as good as the 7.5 or the 18.75. But it still hits them hard.

As I mentioned below, the higher the conductivity, the better the 3 kHz responds. I ran several hundred coins past each of these coils. On all the nickels, the few gold coins I have, a small handful of the older IH cents and for an unknown reason, a few select wheats, the 7.5 does just as well or better than the 3 kHz. And on those coins with lowest conductivity, the 18.75 does even better than either the 7.5 or the 3 kHz. But honestly, neither the 7.5 or the 18.75 are going to make me take that 3 kHz coil off when I'm coin hunting open areas. Not unless I get into a spot with half dimes and silver 3-cent pieces. That is where I am now with my airtests. I'm trying to define that point where the lower frequency's ability to be better on higher conductive targets "gives way" to the higher frequency being better on the smaller targets. Right now, my tests are inconclusive because there are many more considerations (in an actual field hunt) than what an airtest can provide. But like I said, it keeps my mind occupied! HH Randy

 

[Donut]

Great info thanks Randy.

 

[lurksalot]

n/t

 

[sonny32]

I did the same test and also recorded the ID's of each target including a 4 gram gold nugget but all the coins I used were of the era in which I expected to find,,All coins predated 1950 including a dollar piece,and a Large cent,,, And as soon as I find the paper that I wrote it all on I will pass on the information......