High perforance large 36" coils?

[Infamy]

Is this one of those ox+morons? I have the feeling that there is nothing to be gained in building a high quality large coil, (based on
geotech1 forums) but I'm not so sure. Has there been much focus on this field? If you had a coil that could change shape would it need shielding? I ask that question as it may help in depth or size prediction. Thanks

Performance not.

[Carl-NC]

Big coils can find big targets deeper. Large coils tend to be limited to PI mono coils which are easy to build. Large IB coils for VLF are more difficult, especially mechanical stability. However, Nexus makes a 41-inch IB coil for their VLF models. They also make 32" and 42" concentrics for Minelab PIs.

[Infamy]

I was reading up on Litz wire last week and they are listed with strand size and frequency, can this be used to improve performance, eg 10/30 being listed for 1-10KHz.

[Carl-NC]

Litz is commonly used in higher frequency detectors like VLF gold models and PI. Mostly on the transmit side.

[Infamy]

I'm asking the question about Litz because I don't fully understand PI pulse and how that relates to frequency. Is 300 pulses closer to 1KHz than say 1000 pulses or is it something different?

If I use carbon fibre rods to stiffen a light weight plywood coil base, will that create problems? I plan to do a paint on shield of say 2- 3 inched wide that will be running on top of the ply under the coil.

PS I'm reading ITMD3 along side watching Woody's coil videos, this helps me with the tricky stuff. Having just bought a working Sovereign in need of total servicing, I'm looking forward to Opening up the Metal Detector; its a much larger market.

[Carl-NC]

With PI it's less about pulse rate and more about the speed of the pulse itself. That's why you need high bandwidth.
Not sure about the carbon fiber rods, might depend on how they are used. My guess is they won't cause any problems.

[GeoMax]

"..... Is 300 pulses closer to 1KHz than say 1000 pulses or is it something different?....."

.

Hi Infamy,

now I understand why you were asking before in another post for complete building manuals for the Delta Pulse detector. FYI... 1kHz is 1000Hz and 1Hz is 1 pulse per second (pps). This should answer your question above.

[Infamy]

Del

[Infamy]

Hi Infamy,

now I understand why you were asking before in another post for complete building manuals for the Delta Pulse detector. FYI... 1kHz is 1000Hz and 1Hz is 1 pulse per second (pps). This should answer your question above.

Thanks just the sort of info for OUT MD. For setting up a damping resistor can you use an adjustable instead of having to swap resistors. Is there any benefit to fine tunning, is that even possible?

This is very much the last part of a project I've had going for more than 20 years on and off. Basically low cost high precision semi autonomous surveys using numerous detectors to build up a picture of a target. I use to work in the mining industry in Australia doing surveying and gps machine guidance. Before that I had been trying to locate a hoard of silver but it eventually occured to me that it was located in an estuary and I would need a whole new approach.

So after leaving mining I built mini survey vessels and detector barges and tested using basic gps until the system worked. Now besides building the detectors and coils what is left is figure out is optimum swing speed and search patterns.

Back to coils, I might build two large mono coils, one in copper tinned strands to iron problem then one in litz and see what the differences are. I'm particularly interested in sound variation, I record the sounds and I know from fixing hifi systems the high quality even new capacitors can improve a sound system. A shame Minelab takes a dump over all theirs. Probably illegal in the EU along with inability to use different coils, maybe a file needs to be opened.

PS for OUT MD what does "high bandwidth" mean Carl, thanks.

Is there and advantage is using 1.6 dia litz compared to 1mm litz.
Thanks

PPS. I would hold on to all your Minelab bills.

[GeoMax]

.....Is there and advantage is using 1.6 dia litz compared to 1mm litz.
Thanks.... .

Hi Infamy,

Actually, it depends on what your transmitter circuit looks like. It also depends on how many strands your litz wire has. For example, I would prefer a 1 mm diameter wire with, say, 48 strands to a 1.6 mm diameter stranded litz wire with only 16 strands. Of course, the TX circuit and the damping resistor must be adapted to the coil.

[Carl-NC]

PS for OUT MD what does "high bandwidth" mean Carl, thanks.

Usually high bandwidth (>1MHz) is needed for early sampling (<10us) that increases sensitivity to small gold (nuggets or jewelry). If you are looking for a big silver cache then you don't really need to sample early (25us should be OK) and therefore you don't need such a high bandwidth. Also, litz is used to improve a high-bandwidth response, probably won't help with what you're doing.

[Infamy]

[QUOTE=GeoMax I would prefer a 1 mm diameter wire with, say, 48 strands to a 1.6 mm diameter stranded litz wire with only 16 strands.[/QUOTE]

Would this apply to tinned stranded wire, & why?

[Infamy]

Also, litz is used to improve a high-bandwidth response, probably won't help with what you're doing.

Probably.

[GeoMax]

Would this apply to tinned stranded wire, & why?

Not really,

stranded tinned wire is a different type of wire compare to litz wire.

[Infamy]

I'm guessing that there is not much hard data in the public domain that has investigated large coils made of litz wire due to the cost. Small coils & gold seems to be well understood, but at over 120 Euros for ever experimental large coil, its a bit prohibitive for an individual.