Fisher F70 Coil help

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Fisher F70 Coil help

Post by skunkrider2 » Wed Jan 03, 2018 10:48 pm

Hi all, bought a fisher f70 a week ago. Took it to beach last weekend and after 4 hours had found nothing. thought nothing of it until today when I placed a 5p coin and a gold earring on the floor and tried to see if detector would pick up the signal. It has no trouble at all finding coin, but very poor at the gold earring?
My question is, should I change the coil for a better one (as far as I know it has the standard coil on it , as it says F70)
I have reset detector back to factory settings, but was shocked at how poor it was at finding gold????? as I thought these machines had good name.

Any help would be appreciated as I'm new to metal detecting and after spending £350 on the machine don't particularly want to spend another £150 on another coil. :-SS

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Re: Fisher F70 Coil help

Post by Blackadder43 » Wed Jan 03, 2018 10:58 pm

What sort of gold earing was it?
If its a hoop they are notoriously difficult to pick up..
Same as gold chains, in your hands it might appear to be a decent lump of gold, but its only small touching links that holds it together, so the detector often only sees individual links
I'll let the more experienced beach detectorists and fisher users come in, but thats my bet
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Re: Fisher F70 Coil help

Post by Fusion » Thu Jan 04, 2018 2:22 am

A small gold earring is a very difficult target - not only is it small, thus it gives a weak response, it's also not made from the most electrically-conductive metal. This makes it have a very high "corner frequency" so the ideal detector operating frequency should be similarly high, 30kHz - 100kHz, much higher than your 13kHz Fisher. And just as large targets are found more readily with large coils, small targets are best located with small coils. You'll find the Fisher 5" circular DD coil will find the earring deeper than the stock (10" ?) coil.

And .... regarding the beach environment, the F70 is not the best weapon. Most single-freq machines struggle with the salt-water , especially higher-freq machines like the F70. Coinshooters at 5,6,7 kHz are more stable, but then their low frequency makes them less able to detect gold rings, for which 15kHz - 25 kHz might be best. The 5p cupro-nickel coin is not a bad representation of a ladies gold ring, ID values of 20 - 30 would be expected.

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Re: Fisher F70 Coil help

Post by skunkrider2 » Thu Jan 04, 2018 12:40 pm

Thank you very much for the informative information. I feel a bit better now knowing the machine is working as it should. Maybe I was just expecting too much, with too little knowledge. rl;

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