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New 705 owner - coin ids

jjbunn

New member
I just received a 705, and have been testing it outside against a set of old British coins laid on the ground. I first did the auto ground balance. I'm a bit puzzled by a couple of results, shown in the table below:

  • 1941 Farthing (Bronze) ID = 28
  • 1885 Florin (Silver) ID = 42
  • 1797 Cartwheel Penny (Copper) ID = 44/46
  • 1965 Penny (Bronze) ID = 42
  • 1945 Threepence (Brass) ID = 34/36
  • Gold Ring ID = 18
  • Iron Nail ID = -6

So, the two bronze coins show very different ID values (28 and 42) ... is this a measurement error on my part, or a usual variation? I'm also surprised the silver florin IDs the same as the bronze penny - again, maybe my measurement error?

Comments on these measurements would be welcome :)
 

Old Longhair

Crazy Ol' Foole
Staff member
Size (diameter), total mass, and actual alloy composition, all could easily account for the variation(s) that you're experiencing.

BTW, good on you for testing them on the ground. Most people don't get why "air testing" is worthless. :thumbup:
 

Old Longhair

Crazy Ol' Foole
Staff member
jjbunn said:
At least the gold is radically different - no chance of misidentifying that :)
Unfortunately, gold can come in almost anywhere. It tends to be more toward the lower end of the scale, but it's not a hard & fast rule. Again, size, mass, and specific composition all play a role.
 

jjbunn

New member
It's all moot, as all I'm finding in my back yard are nails - I can open a hardware store soon.
 

metalpopper

New member
Old Longhair said:
Size (diameter), total mass, and actual alloy composition, all could easily account for the variation(s) that you're experiencing.

BTW, good on you for testing them on the ground. Most people don't get why "air testing" is worthless. :thumbup:

*********************************************​

Well ......It appears that YOU don't understand the correct meaning of AIR TESTING, ...and the reason why it is a valid function.

AIR TESTING is the method used to obtain the UNIVERSALLY APPLICABLE DATA on a target. (i.e. a coin)

The coin has a definitive VDI related to the FREQUENCY applied/used in the examination, due to its metallic alloys; and dimensions. (ware will modify matters)

Those results are the same ' ANY WHERE IN THE WORLD'......and that is utilizes when scientifically analyzing a coin....

When searching for 'in-ground' coinage, the detector's VDI generally varies due to the local soil conditions....and the same coin's ID can read differently depending on soil 'conditions'.etc.

Different detectors /or design......may produce different VDI's for the same target.



So now you know the full fact ........IN AIR FIGURES ARE THE ONLY ONES YOU CAN QUOTE ....anything else is as variable as the soil you search..!!!!!!!!!
,
 

Old Longhair

Crazy Ol' Foole
Staff member
:rofl: Yeah....I don't understand. That's rich!

Getting a general idea of VID is THE ONLY thing that "air testing" is good for, and when using a machine that has GB Tracking like a 705 has it's best done with the coil on the ground so that the machine has something to GB on, which will give you a more accurate "impression" of what those targets will register in your soil conditions.
Audio nuances of target responses are far more revealing in real world application. If a potential target gives an audio response that is consistent with a coin or ring I'm going to dig it regardless of what the VID indicates.
AUDIO RULES!

Air testing to get any sort of the depth and sensitivity capability of a machine like a 705 is as pointless as it is inaccurate, because of all the variables involved that directly effect conductivity and target response.
 

metalpopper

New member
Old Longhair said:
:rofl: Yeah....I don't understand. That's rich!

Getting a general idea of VID is THE ONLY thing that "air testing" is good for, and when using a machine that has GB Tracking like a 705 has it's best done with the coil on the ground so that the machine has something to GB on, which will give you a more accurate "impression" of what those targets will register in your soil conditions.
Audio nuances of target responses are far more revealing in real world application. If a potential target gives an audio response that is consistent with a coin or ring I'm going to dig it regardless of what the VID indicates.
AUDIO RULES!

Air testing to get any sort of the depth and sensitivity capability of a machine like a 705 is as pointless as it is inaccurate, because of all the variables involved that directly effect conductivity and target response.

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^​

Indeed,,,,you post implies a limited comprehension regarding the science involved and its practical application.

I quote your own words...

Air testing to get any sort of the depth and sensitivity capability of a machine like a 705 is as pointless as it is inaccurate, because of all the variables involved that directly effect conductivity and target response


Now LH, let us see you prove your point, by you DETAILING A FEW TESTS, USING US COINS.... 2 off is sufficient, (homogeneous alloys).

(1) Quote search-head model, frequency, dimensions.

(2) Define sensitivity setting and threshold level.

(3) State Detecting MODE. (Coin?)

(4) Now list Maximum distance in air, that produced CONSISTENT audio tone.

List your IN-AIR results.

^^^^^^^^^^^^^^^^^^^^^^^^^

Now bury the coins at depths ... 'deeper, equal or less than ' the IN-AIR ranges, and lets see how well you've performed the task.

AGAIN...list the 'IN-GROUND' results, so that we may rationally examine the outcome.

Please remember to quote your GB reading for the ground involved....matt
 

metalpopper

New member
New 705 owner - coin ids
Posted by: jjbunn [ Send a Message ]
Date: April 03, 2019 08:08PM Registered: 3 months ago
Posts: 3
I just received a 705, and have been testing it outside against a set of old British coins laid on the ground. I first did the auto ground balance. I'm a bit puzzled by a couple of results, shown in the table below:


• 1941 Farthing (Bronze) ID = 28
• 1885 Florin (Silver) ID = 42
• 1797 Cartwheel Penny (Copper) ID = 44/46
• 1965 Penny (Bronze) ID = 42
• 1945 Threepence (Brass) ID = 34/36
• Gold Ring ID = 18
• Iron Nail ID = -6

So, the two bronze coins show very different ID values (28 and 42) ... is this a measurement error on my part, or a usual variation? I'm also surprised the silver florin IDs the same as the bronze penny - again, maybe my measurement error?

Comments on these measurements would be welcome
******************************************************************************

Hello UK jjbun....

Xterra 705 .....Alas, no indication of what search-coil used, so we do not know at what frequency the testing was done....but the listing is nicely presented and from that I will assume it was a 7kHz coil ...?

Based on that assumption, I will estimate the theoretical VDI :-

The 1941 farthing, quoted as ‘bronze’; is normally 20 mm in diameter.

If it were ‘pure’ annealed copper, its relative conductivity would be 100.

‘Bronze’ as an alloy of copper, and the 1941 farthing I approx. rate at 88.

What then do I theoretically estimate its VDI ?

Theoretical calculations produce, 27.6 Rounded-up, 28 QED.








Now for the 1885 Florin, (Silver) ID = 42
????????????????????????????
1885 Florin..’Silver’......but we ask, “What specific quality of silver dose that equate to?”
Web search:- % silver 92. Diameter = 30 mm.
My estimation of VDI using X-terra 705 @ 7.5KHz. = 43.3...rounded-down....43 QED.
“”””””””””””””””””””””””””””””””””””””””””””
Now for the 1797 Cartwheel Penny; History and Inflation.
By Ozcopper



The 1797 cartwheel penny is an important coin because it is the first coin made using a steam driven stamper, They were made by Matthew Boulton’s famous Soho Foundry in Birmingham.
Each coin contained an (Av) ounce of near-pure .999 copper.
Thus we know copper was worth a penny an ounce in 1797. The weight of these coins also made them ideal as substitutes for weights in measuring produce, a task for which they were intentionally designed.
???????????????????
So, they were ‘pure’ copper ! (99.9%) and 36 mm in diameter.
My estimated VDI then is approx. 47.1 Rounded-down = 47. QED.
<<<<<<<<<<<<<<<<<<<<<<>>>>>>>>>>>>>>>>>>>>






Now for the 1965 penny; (Bronze) ID = 42.
Dates Composition Mass (grams) Diameter mm)




1925–1943, 1945–1954 Bronze (95.5% Cu, 3% Sn, 1.5% Zn)
9.4 31
1944, 1961–1970 Bronze (97% Cu, 0.5% Sn, 2.5% Zn)
9.4 30
“”””””””””””””””””””””””””””””””””””””””””””””””””””””””
The approximate calculations for the 1965 penny initially indicated an ID of 46, but then I noticed an increased Zn content of 2.5, which reduced the ID to 41.5
So rounding that up, gives us the same figure quoted by you 42. QED.

Well JJ..I think that brief assessment of your ‘IN-AIR’ tests demonstrate the significance of the process AND your competence of doing it correctly.
”Well done”
With regardes to the ‘sameness’ of ID’s for differing targets…..
That’s the enigma of single-entity identity limitations method, for the majority of hobby-detectorists who don’t have the deeper, technical background qualifications or interests. That’s not a critisimn; simply a fact of life!
The FREQUENCY factor involved in all these complex calculations plays a major role. If you use a relatively lower frequency, then depending on the ‘other’ factors involved, the target’s ID significance will be ‘more individualistic.’
Because you GB’d initially, and coins were on its surface; its contribution was negligible.
Perhaps you can therefore appreciate the ‘benefits’ of the E-Trac’s 2 dimensional VDI methodology.
I hope you enjoy your Xterra…its lightweright…its options…..and its limitations.
At 18 KHz, its gobbles up the thinner class of coins, rings etc ( 1 mm or less)
……matt
 

Old Longhair

Crazy Ol' Foole
Staff member
While I appreciate your obvious knowledge in general, I must say that I find it almost comical that you jump in to challenge my statement, then lay out a list of parameters for ME to perform a test with to prove YOUR assertion, and then in your next post you note "other factors" that include variables that affect ID accuracy. Frequency selection has a bearing on more than just target response, because the ID segment bin widths also vary between frequencies with an Xterra, and it does affect ID accuracy..
When you ask for GB numbers in your test parameters, are you expecting me to run w/o GB Tracking turned on? (something that I virtually never do)
Do you allow, anticipate, or take into account that I may run Tracking with Offset? (I often do)
Do you find any deviation between the response produced by fresh planted targets and those in an environment where the soil matrix is undisturbed prior to digging?
And finally, do you only dig targets that produce a consistent ID? (I don't)

Perhaps we can get YOU to run your test with your parameters, and report back with your findings. That could be very interesting and informative.
 

metalpopper

New member
Old Longhair said:
Perhaps we can get YOU to run your test with your parameters, and report back with your findings. That could be very interesting and informative.


Thanks for your reply LH.....I will do that as soon as local weather conditions improve...(Heavy rain storms locally)....matt
 

metalpopper

New member
[attachment 369930 Testin705Coindata-2.jpg]

Well LH, at last I've managed to test a couple of US coins, and list the results.

You can see the 'In Air VDI at the recorded ranges.

Compare those to the indicated VDI as each coin was incrementally inserted into the soil of my garden's lawn.

At an inch or two depth the VDI climbed higher and became erratic, until the audio response ceased.

Now you can hopefully understand why I wanted you to personally do the same type of test, and then

tell me and other readers, what you thought about the 705's VISUAL performance.

This was all done using the 9x5 inch elliptical coil operating at approx.18 KHz.

Maybe other readers will do the same kind of tests using other frequencies coils?

Whenever I used the 705, I only use two-tones....and set my rejection level at about +6.

Anyone have any comments on the 705's visual VDI vagaries?......matt
 

metalpopper

New member
So LH advocates tonal response rather than Visual Indication by numbers.....
r
I acknowledge his reasoning, based on the fact that the 705's limited ability to better resolve a target's VDI as its depth increases.

My posted tests illustrate two typical examples.

So how then is Tonal differentiation more informative, when the tone's 'pitch' is related to the VDI's value ???

Under such circumstances, I prefer the simplified TWO-TONES audio mode.....Low = Rejected, and High = Accepted.

Then, if the target's shallow enough, I can relate its VDI to my experience of [size=large]IN-AIR classification[/size] grouping.

Ultimately....you simply 'dig-it' ....and compare reality with your anticipations.....that's the limitations of the 705.

The 705's excellent user interface, is marred by its poor 'target resolution at depth'.

Presently, I only have the 9x5 18 Khz elliptical to relate to, but suspect the concentric coils may offer an improvement.

Any comments from 705 users regarding other coils?.....matt
.
 

Old Longhair

Crazy Ol' Foole
Staff member
metalpopper said:
So LH advocates tonal response rather than Visual Indication by numbers.....
r
I acknowledge his reasoning, based on the fact that the 705's limited ability to better resolve a target's VDI as its depth increases.

My posted tests illustrate two typical examples.

So how then is Tonal differentiation more informative, when the tone's 'pitch' is related to the VDI's value ???<snip>
.
What you've failed to grasp is that tonal response involves more than simply pitch. There are tonal nuances that play heavily in determining whether I deem a target worth digging or not.
 

metalpopper

New member
Old Longhair said:
metalpopper said:
So LH advocates tonal response rather than Visual Indication by numbers.....
r
I acknowledge his reasoning, based on the fact that the 705's limited ability to better resolve a target's VDI as its depth increases.

My posted tests illustrate two typical examples.

So how then is Tonal differentiation more informative, when the tone's 'pitch' is related to the VDI's value ???<snip>
.

What you've failed to grasp is that tonal response involves more than simply pitch. There are tonal nuances that play heavily in determining whether I deem a target worth digging or not.

************************​

Rick.....You've not answered my post regarding the 705's VDI on two sample US coins....Why?

As for tonal nuance, and your interpretation , well that is a personal matter...dictated by your settings and sweep 'modus operandi'.

Can you apply your 705 experience to the charted results posted, and comment?.....matt
 

metalpopper

New member
Found this post on a Minelab com. related forum; just one of many similar opinionated commentaries.


Jeremy on July 1, 2018 at 04:21

I don’t agree........ For one, tests of these sorts are not limited to post purchase. Some people will look at data to decide if it’s what they are looking for. Even where that is not the case and it’s a post purchase interest, air tests and test gardens are very useful. An air test will tell you what you should be able to do in mild ground. Remember that the argument against air tests is that they are not representative of real world conditions. Well that’s only partly true. That depends on your level of mineralization. And if air tests and garden tests were not instructive, we would not see the deepest machines always putting up the highest numbers. So air tests are informative to the extent that they will show you what you should expect as a maximum under ideal conditions. Garden tests are informative if they are qualified by the settings used and the mineralization level of the soil, as well as maybe the region. Back when machines were limited to 6-8″ of ground all this old timer bluster about testing was more relevant. Machines are hitting deeper and they are unmasking better etc. There are more disc features and so tests are helpful. Experimenting with features and combinations and testing against the baseline is helpful to determine if your getting the most out of a given machine or if you want it in the first place. .
 
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