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Cache searching using Standard model F75 (also Eqx)

Posted by Pimento 
Cache searching using Standard model F75 (also Eqx)
September 26, 2015 01:23PM
I had been intending to start this thread for a while, but the other recent thread (on CL mode) reminded me:

I'm detecting European farmland, searching for non-ferrous items. I have done quite a few trial runs at this over the past year, but I would be interested to see if you experts could contribute, too.

I'm using a Standard model F75, with the stock 11" x 7" coil. I'm using 'Stat' non-motion all-metal mode, with the coil at about 14 inches clear of the ground. Ground Balance is functional in this mode, and I have found that setting it in the GB = 40 -> 50 region will give a 'positive' ground response. I'm holding the detector stem at the lower end of the S-bend (for balance), and I've found that the trigger-switch can be be deftly pushed back with the back of my thumb to re-tune the threshold when needed. Having the positive Ground response means I can fine-tune the threshold by slightly raising/lowering the coil height, and if it seems to have drifted off enough, I can then re-tune it. Physically, I'm walking 'lanes' in a straight line, not swinging the coil, though if I get a 'hit', I will slowly swing from side-to-side to get the pinpoint. Having found a target, I then use the detector 'normally' and see if it's iron (99% of the time it is, usually medium large, and shallow).
So far, I have had one 'success', a 150 gram ( 1/3rd pound) lump of lead at 10 inches, though this would likely have been detected 'normally'.
My feeling is the stock size coil is too small for this job, a 13", 15" would go deeper.

What have you guys done, any tips?

Edited 3 time(s). Last edit at 08/28/2021 12:46PM by Pimento.
Re: Cache Searching with the Standard model F75
August 23, 2021 07:01PM
Sounds like a very interest project,i have a basic idea on what you are doing and it certainly is very interesting in what you are trying to achieve.

As i have my Nexus with the dual 9'' coils and a Fisher TW-5 twin box i guess i could use it in a similar fashion with either of these machines.

May give it a go with both of these machines this coming weekend on one of my local permission,smaller targets are getting harder to find,bu as i am right next door to the main roman road going north its possible than items are much deeper than say what a normal detector with a stock coil can reach.

Have been aware that you have mentioned this method before but never tried it myself that is when both the Nexus or twin box could come into play.
Re: Cache Searching with the Standard model F75
August 23, 2021 07:50PM
The SEF 15" X 12" will get inches more depth than the stock coil on coin-sized targets in clean unmineralized ground and get incredible depth on cache-sized targets. I had it on my T2 and F-75 for years and was amazed at the difference in depth compared to the stock coil in my test garden.

Fisher does not make very good coils, IMO.

I tried the Ultimate 13" and it did not seem to offer any advantage over the stock coil. I also tried the NEL Attack and Thunder and while they did get good depth, they seemed heavy and out of balance compared to the SEF.

Edited 5 time(s). Last edit at 08/23/2021 08:07PM by Badger in NH.
Re: Cache Searching with the Standard model F75
August 23, 2021 09:04PM
Thank you, J&D for taking the time to reply.
I never did get a Fisher 15" coil, they rarely came up for sale, and the prices did not seem attractive ( I wanted it cheap ).

I now also have the Equinox, and have tried this technique out, using the stock 11" coil. It has promising performance, and I did recover a couple more deep non-ferrous items that would possibly have been missed if detecting normally. The self-adjusting pinpoint function can be troublesome at times, but with care it can be worked around. I have secured a short-term loan of the ML 15" coil for the Eqx, and will do some tests with it, as well as real-world trials on cultivated farmland with plenty of history.

As an offshoot of a thread on Geotech1 about testing machines, I came up with a standard "Large Test Target", which I've used for a few experiments. It's reproducable, with some effort, so other people could make their own and do comparisons etc.

Test Target 1:
A cast lead disc, 60mm diameter and 5mm thick , made from 150 grams of lead.

No picture, but it's plain to see it's a giant coin. The round shape gives it symmetry, so swing direction issues won't occur, but also allows for 'on-edge' tests. It's also slightly representative of real world targets - lead pots were sometimes used as the container for coin caches, and large lumps of lead casting waste are not uncommon here in Europe.
It can be simply cast in a thick aluminium foil mould. I made mine from the foil used for food products, like pies, ready-meal trays etc.

The Eqx with 11" coil can detect this at 70-75cm / 27-30 inches in air, using pinpoint mode.

And thanks, Badger:
I did briefly try out a Mars Tiger on my F75, and found it most disappointing. It's definitely a tricky machine to get the 'right' coil for. I hoped the Fisher coil would work for non-motion hunting, even if it was underwhelming ( like so many state ) when used for general searches.

Edited 3 time(s). Last edit at 08/28/2021 12:50PM by Pimento.
Re: Cache Searching with the Standard model F75
August 23, 2021 09:17PM
@Pimento,i had the same bad experience with my Mars Tiger coil on my T2 as well,although i still have it but not used it for maybe 2 years.
I will agree that the SEF 15x12 Coil which you repaired does work exceptionally well on not only small coin size finds but also much bigger finds,possibly one of my all time favourite combinations.

The jury is still out on my Nox and have all 3 coils but still have a love/hate relationship with this detector...the T2 still is my favourite detector and certainly found me the most gold coinage by a mile.
Re: Cache Searching with the Standard model F75
August 23, 2021 11:14PM
Pimento, is your objective to get cache-sized objects ? (as the title of the post implies) ? If so, then if I were you, I would not be using a coin machine, of any sort, at all. Instead, why not just get a 2-box machine ? Like a Whites TM-808 or similar ? They will not find an object smaller than a tennis ball or soda-can size. Thus they are the perfect discriminator for all small items (tabs, foil, nails, individual coins & rings, etc.....).

I realize that some people will say that by-the-time you add on a really big coil to a standard machine, that the depth is probably just about equal for toaster-oven-sized objects . But the problem is, you will be bedeviled by hearing all the normal coin-sized stuff. Even if you try to put your mind to "ignoring all the small beeps", yet you will be perpetually digging a bunch "just to be sure". Because go figure : A mason Jar or shoe box sized target, at 18" deep might mimic a half dollar at 3" deep. Contrast to using a 2-box machine, you simply hear none of the small target in the first place.
Re: Cache Searching with the Standard model F75
August 24, 2021 02:19AM
@Tom in CA,must admit that is the route i would of also gone down as well,i have the Fisher twin box which is basically exactly the same as the Whites TM-808 and if you are only interested in the real deep larger than tennis ball size items and larger then a twin box is the way forward.

I picked mine up some years back with possibly 1 hours use for stupid low price less than what you would pay for a stock coil,so even if it comes out to play say once a year it does not owe me anything.

But i will possibly dig it out again is week and play with it again on my roman site.
Re: Cache Searching with the Standard model F75
August 24, 2021 01:34PM
"Why not just get a 2-box machine ? Like a Whites TM-808 or similar ?"

A few reasons:
*I don't want to spend much money, so would prefer to use what equipment i already own.

*Based on info generally gleaned from the web, they aren't that good on caches; for example when Carl Moreland recreated the 'Gary's Hoard Test' , he tried many machines/coils, including some two-box units, and they were universally a fail. ( Deus with large coil was one that got it, but running at 18kHz, I recall .. I'll find some links later )

*They seem more suited to very large targets, at significant depths. I'm after moderately large, at more modest depths, and I feel a good conventional machine with a decently large coil would be capable of this.

* I'm unsure about the discrimination capabilities of the various two-box units, so it would be a tedious process involving marking some targets then going back with a conventional machine to investigate further. The land I'm searching has been heavily used for centuries, and has huge numbers of large iron targets, one every 2 or 3 metres in some places. A ten acre field could have 5000 such trash items in it.

I have wondered what the 'equivalent coil size' for a two-box machine is. My hunch is 1.5 to 2 metres. It's not an easy one to measure, a mathematical simulation would be one way. Over on Geotech1, we did discuss comparing mono / DD / concentric behaviour, but two-boxes were never mentioned.

Edited 1 time(s). Last edit at 08/28/2021 12:52PM by Pimento.
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