GPX4500 - discrimination - coins & relics

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GPX4500 - discrimination - coins & relics

Post  dabber on Sun Apr 19, 2009 1:59 am

Hi all,i live in europe (belgium) and i use the gpx4500 for coin and relic hunting.
The fields where i search for antic coins and relics are mostley much iron crap.
i use the 4500 now for 1 year and i think i could handle it well.
the problem i have,is when i use disc,even only set at 2 ,the treshold blancs out good things that i don't want to loose.
my englisch is no good bad i try to explane and hope somewhone coild tell me of this is normal ore is the 4500 faulty.

when i come to near with the coil to a good target,it depend on how big is the target,lets say a brass statuette of 100 gram. the treshold blanc it out,the machine is not overloaded .if i set disc off its keep giving a good signal even when i hold the coil verry near to the target.
little coins are not so a problem with the disc at 3,they give a good signal only when i hold the coil verry verry close to the coin somtimes it blancs out.
the coins that i search have a whight from 0,5 to 6 gam.
i send u a picture of a coin i found with the gpx 4500.
it is 1,2gram and a dia of 12mm, the gold percentage is 49 procent.
the coin is from the year 670
value=+/- 3000euro.
i hope somewhone could help to my problem,because i don't want to lose wanted targets because this.
thanks in advants

dabber
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Re: GPX4500 - discrimination - coins & relics

Post  alchemist on Mon Apr 20, 2009 11:15 am

G'day dabber,
What coil are you using?
The manual says iron reject will give the best results when a specially designed GP series, or Commander DD (Double D ) coil is used. They will have the balance phase set correctly.

Do you have the Coil/Rx switch in Double D mode?
I know from experience that if the switch is in Cancel mode, it can cause good targets to be rejected, and M (mono) will cause iron reject not to work.

Also what Ground Balance type is selected?
You should use General and run it in Fixed.

Additionally try using the factory preset custom search mode Hi-Trash with the settings mentioned above.

Hope you get it working OK.

Cheers
Grey
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Re: GPX4500 - discrimination - coins & relics

Post  dabber on Mon Apr 20, 2009 3:13 pm

Hey grey i use the standaard 11 inch DD Commander +5x10DD +the 12x15DD Commander.
RX switch in DD.
Mostley i run the 4500 in special extra,or scharp because the soil is mild here.
groundbalance type general/fixed
Motion/slow
Man tuning for the best result.
audio/normal somtimes queitt.
i now nobody else here around ho's got a 4500,so he could do the test with his machine.

custom hi-trasch use disc at 6 and thats far to much,i would say try it on a peace of brass and let me now.
Thanks for your response.

groeten

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Re: GPX4500 - discrimination - coins & relics

Post  alchemist on Tue Apr 21, 2009 7:46 am

Hi dabber,
Is this an ancient piece of brass you are testing with? If it was made before the 18th century it will be calamine brass which is alloyed with a zinc carbonate, and if this is in the form of hemimorphite, it may contain iron oxides and other impurities that could affect discrimination. Especially so if the zinc was mined from surface gossans, highly likely if you are using a test piece from the ancient Greek, or Roman era.

I'll test a piece for you once I know if the test piece is modern or not. The disc is highly biased towards gold, and may give bad indications for other metals not having the same conductivity index, certainly alloys such as brass and bronze may be seen as undesirable whereas copper may not. It all depends upon how the discrimination circuit works, and I'm not certain about this, but it probably looks at the reactive component of the signal which should mean that only magnetic targets would be discriminated. If you've got a strong magnet, such as one from an old computer hard drive, does holding this up to the brass give a slight attraction?
How does your 4500 disc respond to gold and silver coins?

Cheers
Grey.
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disc

Post  dabber on Tue Apr 21, 2009 3:14 pm

HI grey,modern coins like a 50eurocent or even a peace of lead makes the treshold blancking away,before the 4500 i have the 4000 for a while and the same thing with that.
I thank you verry much for your response.

geert

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