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Bounty Hunter II coil shielding question

BFO Guy

New Member
Joined
May 18, 2020
Messages
23
I just picked up an old Bounty Hunter II in like new condition. This is one of their early BFO’s. I am wondering if they had faraday shields on their coils. I can put the coil on my hand and I don’t notice any effect but if I wrap my fingers part way around the coil (its an open loop) it has a nulling effect. The coil is inside a potted body so I’m not physically deforming the coil. I notice a similar but much less noticeable behavior when doing the same test on my home made BFO on which I implemented a wrapped aluminum foil shield. But on that one the coil is not potted. It is only taped so I’m sure I’m compressing the coil a little.
The Bounty Hunter almost certainly is shielded or it would react to my hand when just getting close. It seems ok until I wrap my fingers part way around it.

Is the shielding just not good enough or what?

Is there a shielding technique that will totally eliminate the capacitance effect of wrapping my fingers around the coil?

Well......just as I was typing these questions I had a thought to test something. I put my hand across the bottom of the coil and there was little to no effect. I put my hand across the top of the coil and it nulls. They only shielded the bottom! I guess they used a carbon sheet or some other flat shield on the bottom? I guess it’s cheaper and easier to manufacture that way.

I guess I answered my own question but maybe it’s interesting to someone so I’ll leave it here. lol.
 
I have 1980s Fisher VLF 551-D and do agree with your concept. The coil is BFO with VLF GNC discriminator.

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The Bounty Hunter 1/2/3 had shielded coils. But they run at 1MHz, the highest frequency I've ever seen in a BFO. As such, it is probably the body salts in your skin it is reacting to. The high frequency also causes most nails to be detected as non-ferrous.
 
BFO Guy: said:
I just picked up an old Bounty Hunter II in like new condition. This is one of their early BFO’s. I am wondering if they had faraday shields on their coils. I can put the coil on my hand and I don’t notice any effect but if I wrap my fingers part way around the coil (its an open loop) it has a nulling effect.

The coil is inside a potted body so I’m not physically deforming the coil. I notice a similar but much less noticeable behavior when doing the same test on my home made BFO on which I implemented a wrapped aluminum foil shield. But on that one the coil is not potted. It is only taped so I’m sure I’m compressing the coil a little.
I'm sure Carl-NC answered your questions, and I agree that it is typical for your body salts to be causing the audio response from your hand. Some folks are 'saltier' than others and we used to have a lot of fun with many of those earlier detectors doing those 'hand' comparisons of people.



757vnvn: said:
I have 1980s Fisher VLF 551-D and do agree with your concept. The coil is BFO with VLF GNC discriminator.
Your VLF Fisher 551-D does not use a BFO coil. It is a VLF (GB All Metal mode) / TR-Disc. that operated at 4.5 kHz.

Monte
 
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