GPX 17 Coil Commentary

[Swegin]

On 8/15/2021 at 5:34 PM, 1515Art said:

Bluetooth device from Amazon

Which did you end up buying?

[VicR]

Hi G - i think you gave more away trade secrets as the test bed was in South Australia - so looking forward to visiting the Golden Triangle Victoria  again when the borders are open and giving the 14 inch DD a go.

Now where exactly was your patch?😊

[1515Art]

11 hours ago, Swegin said:

Which did you end up buying?

This one

https://www.amazon.com/Bluetooth-Transmitter-Receiver-SONRU-Headphone/dp/B08B3P7GH1?pd_rd_w=lAznU&pf_rd_p=f8048a1b-0abf-4d1a-a91b-cb558d45ad96&pf_rd_r=YT77C9CPKQYCE292ZTE4&pd_rd_r=6cb92448-c735-4873-8dc2-cb533b1933cf&pd_rd_wg=8vLb6&pd_rd_i=B08B3P7GH1&psc=1&ref_=pd_bap_m_rp_12_sc

 

[afreakofnature]

15 hours ago, VicR said:

When i used to work in Papua New Guinea the local saying was "expect the unexpected" which i think applies to metal detecting - you continue to learn and be surprised.

Yesterday three of us decided to test the GPX6000 with 11 inch mono, 14 inch DD and 17 inch mono and GPZ7000 with 14 inch stock coil at a local test site that has targets in situ for a number of years.

We were particularly interested in the deepest target that was buried at 400mm (about 16 inches) representing a large deep nugget.

The 7000 could not detect it in difficult setting only in normal setting -  i was told by the owner of the 7000 that normal is not his preferred setting.

The 6000 could not detect this deep target  with the 11 inch and even the 17 inch (we tried all settings)   - but get this - the 14 inch DD with EMI cancel on could hear it as good as (if not better) than the 7000 in normal mode . We were not expecting this result.

We though about this for a moment and the only conclusion we could come to was that the high environmental EMI was affecting the performance of the other coils & favoured the DD coil.

Any other thoughts as to why we had this result?

 

Hey Vic (and G), I have a couple questions.  Vic, what was the target size?  Vic and G, do you think that because the DD should smooth out the threshold/EMI/ground that you were able to hear subtle repeatable targets or was the threshold still a little chattery but the target signals was obvious?  

Thanks!

[Steve Herschbach]

20 hours ago, VicR said:

When i used to work in Papua New Guinea the local saying was "expect the unexpected" which i think applies to metal detecting - you continue to learn and be surprised.

Yesterday three of us decided to test the GPX6000 with 11 inch mono, 14 inch DD and 17 inch mono and GPZ7000 with 14 inch stock coil at a local test site that has targets in situ for a number of years.

We were particularly interested in the deepest target that was buried at 400mm (about 16 inches) representing a large deep nugget.

The 7000 could not detect it in difficult setting only in normal setting -  i was told by the owner of the 7000 that normal is not his preferred setting.

The 6000 could not detect this deep target  with the 11 inch and even the 17 inch (we tried all settings)   - but get this - the 14 inch DD with EMI cancel on could hear it as good as (if not better) than the 7000 in normal mode . We were not expecting this result.

We though about this for a moment and the only conclusion we could come to was that the high environmental EMI was affecting the performance of the other coils & favoured the DD coil.

Any other thoughts as to why we had this result?

 

DD coils back in the day were the go to coils on early Minelab SD and GP PI detectors, and it was not until the GPX series that a switch was made more towards mono coils, as the GPX design tended to favor those coils. However, DD coils do have inherent ground canceling abilities that mono coils lack, and in the case of the GPX 6000 extra EMI canceling properties (or salt, depending on the setting). Your guess as to what produced the result is as good as any, and shows how preconceptions based on simple tests can run afoul of reality. People have generally been writing the DD coil off as a no go due to simple depth comparisons in ground where the DD coil has no advantage. But in this case it shows that the GPX 6000 DD coil does have a place, and can produce good results. Areas with high mineralization, salt, and EMI, alone or in combination, may benefit from use of the DD coil. It's not that the DD coil goes deeper, it is that it loses less depth than other coils in certain adverse conditions. It's being included as the option in the U.S. and Oz for that very reason.

[Jonathan Porter]

EMI/Sferics are depth killers, this is why the GPX5000 came with the Stabilizer setting set on half way, however the GPZ7000 is far better for Sferic noise than the previous GPX machines but can suffer from it nevertheless. Salt is also a depth killer, in a lot of ways it is far worse than EMI due to swing speed having such a variable interaction with the noise generated (from micro variation to excessively loud depending on the location and speed of the coil).

400 mm is not that deep relative to what both these machines can achieve, I’ve dug stuff not much bigger than a gram at similar depths in the right locations, so I would say there was a combination of Salt and EMI present at the test site.

IMHO the Salt mode has better outright depth compared to Cancel assuming EMI is minimal (Cancel is the default setting when a DD coil is attached to the GPX6000) , Salt mode does have some noise cancelling characteristics so if the EMI/Sferics is not too bad then I will use that first before going to Cancel mode. There is a good reason for having a 14” coil size as the default DD coil with the GPX6000, essentially the Rx of GPX14DD it is a 7” Monoloop so the sensitivity to surface targets is off the charts but also the 14” overall size brings up the depth which is compromised when using a Cancel or Salt Tx/Rx format compared to a traditional DD receive or compared to to using a dedicated monoloop coil.

When using the DD, small targets are most sensitive on the left hand edge of the coil with some sensitivity in the centre like a traditional DD, for deep targets the whole left winding is alive with the bulk of the deep signal coming from the centre. It helps with visualisation to think of slower broad deep target noises coming from the centre of the coil. 

JP

[VicR]

7 hours ago, afreakofnature said:

Hey Vic (and G), I have a couple questions.  Vic, what was the target size?  Vic and G, do you think that because the DD should smooth out the threshold/EMI/ground that you were able to hear subtle repeatable targets or was the threshold still a little chattery but the target signals was obviou

Hi FON,

I was told the target was a largish piece of lead (maybe an oz) at 400mm, it & other targets was buried many years ago by a very experience local detectorist - now i have recovered a .5gram nugget at about this depth (same as JP) at Tibooburra NSW (desert country) with the 11 inch coil so i was very  surprised i could not pick it with the 11 and 17 inch mono coils on the 6000 but the DD 14 inch signal was clear as a bell. We had 2  6000 machines with us and both achieved the same results.  Also the 11 and 17 inch coils did not sound overly unstable - only when you put them up in the air could you tell you were in a high EMI area. After the testing we went detecting - I kept the DD coil on and could go right up to an electric fence without hearing the pulsing  - my mates with the 7000 and the 6000 with mono coil had to stay well clear of the fence as it made their machines very unstable.

JP and Steve - thank you for sharing your insights and contributions. Makes me realise i need to understand the environment and ground better to make the correct coil & setting choices. Nothing beats experience.

Also i have a unsubstantiated but credible rumour (apologies if this has already been report) that Minelab has already given a 3rd party permission to design and make coils for the GPX6000.

[dig4gold]

Are you not specifically referring to higher mineralised grounds. What about very mild ground & DD verse Mono. You still think the DD has it over a mono? Cheers 🙂 

 

[MSC]

JP, I have had tennis elbow a couple of times in the past, I purchased an elbow "sleeve" I guess you would call it. It took some time but eventually ( within months ) it healed and have not had problem's for a long time.  The tightness and heat to the elbow it provided is what helped me. Hope you get better. 

[PhaseTech]

On 8/18/2021 at 9:29 AM, VicR said:

Hi FON,

I was told the target was a largish piece of lead (maybe an oz) at 400mm, it & other targets was buried many years ago by a very experience local detectorist 

 

Hi Vic, myself and two other customers set up that test bed initially to test a range of coils. It was just supposed to be for a quick comparison, so we did some crude measurements and target size estimations, most of which have since been forgotten. But the targets have surprisingly remained buried for many years, and I have used the test bed so many times now that I know how different machines respond, so I have avoided the temptation to dig them up and record the weights and depths accurately. I still may do that some day. There is a hackly bit of lead, about 2.5g that is also buried quite deep, and this is a great "challenge" to newbies with any machine, as coil control and positioning is critical. 

From the best of my memory the largest target is a 7g lump of lead, and depth was initially at about 45 cm. The ground to the side of the hole is quite mineralised clay, so mono coils in Normal timings often perform poorly. 

The best combos I've found on this target are: 

Any GP series machine with Detech 15" DD coil

GPZ7000 in General/Difficult 

GPX4500 in Enhance with 12" Evo

GPX5000 with 17x13" Evo (Enhance or Fine Gold). The Commander 15x12" also responds well 

The 15" Evo & Detech 15" super deep also gets it easily, but the signal response is broader, not as crisp as the 17x13".

The 6000 with 11" mono really struggles. The 14" DD in Normal and Salt is the best combo. 

Ground moisture and EMI levels vary the results slightly, which can be quite interesting.