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Treasure Hunting & Metal Detecting Forum Message Boards - Detector Hunter Whites Minelab Tesoro XP > General Discussion - By Location > Treasure Hunting Abroad >

Detecting in South Africa

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gambol1

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	Re: Detecting in South Africa « Reply #2330 on: April 14, 2012, 06:32:40 pm »

Pgill, I borrowed a friend's 9x12" ace 250 coil and did an air test with it. It made a 1" difference in depth. The ground test difference may be greater. It does give a wider sweep and may be worth it for that. It takes a long time to cover a ball field with the 6x9 coil. gambol.

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Pgill

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	Re: Detecting in South Africa « Reply #2331 on: April 15, 2012, 12:34:49 am »

Hi AU Fever, do your self a favour and give the black powder a go, it is a great morale booster Great

this friend also has a black powder double barrel shot gun which we are going to shoot soon.... cannot wait Pray

Gambol, I have been watching the guys on YouTube with larger coils, and they definitely make a great difference, especially on ground coverage... But the depth is deeper. Larger does make the coils not as sensitive on smaller items, but what the guys do is to cover the ground with the large, and if there is stuff, they do that bit of ground again with the small coil.

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God Bless
Peter
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xavier

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	Re: Detecting in South Africa « Reply #2332 on: April 15, 2012, 02:28:09 am »

Hi GD

I think that I know where my problem is. I did the calculation using a 0.47uF giving me an inductance of 210uH for the coil at 16Khz. My coil is 200mm in diameter and only needs 18 turns. This is running at 16Khz and it just does not work. So what I did was I left the 0.47 but I reduced the frequency to 7.37Khz I now have a coil with 35 turns and an inductance of 992uH now things are starting to happen. As I do not have any thinner wire at the moment than 0.35mm I want to use a capacitance of 340nF (330nf + 10nf) in the LC circuit to bring the resonant frequency back to 7.37Khz from 6.23Khz (On the RX side) or should I just use a tuning cap between the bucking coil and the TX coil?

All the best
Xavier

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gambol1

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	Re: Detecting in South Africa « Reply #2333 on: April 15, 2012, 03:49:40 am »

X-it seems to me a 0-15 nf trimmer parallel to the rx coil will let you match the freq.......I've been wondering about my Fisher 75 Elliptical coil. I was forced to open up the connector pod on the coil to dry it out and found it contained a small circuit board with a capacitor and a resistor. Both were parallel to the same coil. I don't know which. I figured the capacitor was for tuning but the resistor? Huh?

? I know more resistance in a tank circuit changes the freq. but it also eats up power. I concluded the resistor must also serve some other function. Possibly dampening the response of the coil?

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xavier

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	Re: Detecting in South Africa « Reply #2334 on: April 15, 2012, 06:53:49 am »

Hi Gambol1

I have made a new coil and like I said previously with more windings, that brought the frequency down but the result is far better I also changed the capacitance on the receiver side and I can now say that I'm 70% happy with it. Now I will make a coil with the same inductance but using 0.5mm wire for the TX and 0.35mm for the RX just to see what the turn ratio will be for the same inductance. I have posted a DOC that I found on one of the thunting threads some time ago, any how it looks a lot like what you have just told me about your coil

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Xavier

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GoldDigger1950

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	Re: Detecting in South Africa « Reply #2335 on: April 15, 2012, 08:59:59 am »

Xavier, in the future, perhaps you might consider taking this kind of discussion to the tech forums. Just saying.

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It's all about that moment when metal that hasn't seen the light of day for generations frees itself from the soil and presents itself to me.

Let's Talk Treasure!

xavier

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	Re: Detecting in South Africa « Reply #2336 on: April 15, 2012, 09:12:03 am »

Hmmm yes I think you're right GD but it sort of just happened. In fact I think that I will start a new thread about coils, should be quite informative.

Regards Xavier

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Pgill

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	Re: Detecting in South Africa « Reply #2337 on: April 15, 2012, 10:05:03 am »

Hi X, glad to see you are coming right with the coil Great

maybe you can now find my gold coins Grin

Are you weekend on or off? Umm we need to find somewhere to get out and do some detecting, this long grass is not doing good to my morale Thumbs Down

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xavier

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	Re: Detecting in South Africa « Reply #2338 on: April 15, 2012, 10:56:50 am »

Hi Peter

Buddy was sick this week so I took over for him and the week before he was on holiday so I stood in for him then too, so I guess that I'm off for two weeks if all goes well Grin

Have you got a place to go and detect? as you said the grass is long but the fires are starting so should not be to long before the good spots will be open again

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Pgill

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	Re: Detecting in South Africa « Reply #2339 on: April 15, 2012, 11:18:49 am »

X, we do not have any fires around our side yet, but one way or another, we need to get out there and find some good stuff Great

Lets do some thinking and see where we can go Clapp

Next Sunday should do great.... normal time Great

I will boot up Google Earth and look around Funny

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