beach use vlf kit or project

[woodbob123]

Which of the many vlf MDs on forum would handle the wet sand / beach best prefer a silverdog kit to a schematic, don't fancy another pi dig too much iron. Hope to spend a few weeks on the coast soon. Thanks

[Koala]

Doubt any will work. All beaches are different. Don't live in your neck of the words but have tried Hunstanton beach with my IDX. Does not work at the pier but can be made to work near the lifeboat station


Done a few around Conwy very hit and miss. Some fine some can be made to work with reduced performance and others where it falls over all together.

Found reducing the sensitivity does not help on the wet and reducing the threshold is the only way. Depending how bad the ground is it may have to be reduced so much that you are only detecting the top few inches.


As another example Talacre where some flat wet areas are okay were a few yard away the detector is unusable

[Davor]

GB of all traditional VLFs expects soil to respond at angle close to TX, while sea water is at 90°. There are 2 possible solutions, but neither are possible with any of the amateur builds. The closest to the possible solution is IGSL because it has a spare channel to act as an extended GB. I have an IGSL, and I intended to employ the 4th channel for the purpose, but sadly couldn't make time so far.

[Tim]

My logic says a Homebuilt BFO or IB could easily be adjusted to compensate for wet/salt/+/-minerals, whereas a paramaterised production vlf will likely not have enough adjustment, or need to be seriously dumbed-down.
I am surprised by the amount of disinformation on the basics which is floating around. The ML owners generally are of the view that PIs can discriminate, because the company tells them so. So the propaganda against earlier technology is born. I relish the opportunity to revisit the solid ironstone areas of the Golden Triangle with my homebuilts, and pull some nuggets from where the PIs and my GMT(lf) fear to tread.
Don't believe anything you hear, and only half of what you see. Theory and practice are often miles apart.

[Gwil]

I'm intrigued. Could you explain how a BFO detector "could easily be adjusted to compensate for wet/salt/+/-minerals"? Thanks.

[Tim]

By simple adjustment of the only(beside volume) external pot. The reason commercial detectors require a different coil for salt is the lack of adjustment range.

[Gwil]

Ok, I understand what you're saying.

[golfnut]

can we add a switch to alter the RC delay to shift the GEB CH clocking the approriate amount for salt ( bit like the black sand switches)

[woodbob123]

I,ve been thinking of rebuilding the Magnum design from years ago as a starting point as that has a beach setting. Also would it help if coil was nulled etc while over the beach rather than in free air?

[Koala]

Even beaches are fine as you can adjust the ground balance to ignore the salt. I can run the IDX just the same as in a field.


Problem is most beaches the ground varies wildly also interesting parts of the beach like gullies go from dry on the side to wet in a few centimetre this boundaries will cause the detector to false.


You can turn everything down until these swings don't cause the detector to sound. This is what the beach mode does on a lot of detectors. Does have a horrible affect on depth.


That doe not include the black rocks you find on some beaches that cause a false signal.

[golfnut]

the dual freq machines seem good on the beach. Or even in the sea. These often have a GEB CH too. Not sure why these win on salt.

With land machines we have the luxury of using ferrite to mimic groung signal phase for development.

Is there a material commonly available to use to mimic salt.

[Koala]

No idea how to mimic the beach. I tried adding salt to a bowl of water and it did not work.


This explains a lot search the page for salt. Link

[Tim]

Maybe a halfway saltwater coil, parameterised between the standard and salt coil, with the machine on fast tracking.

[golfnut]

could get some water discarded from marine tank? or get some marine salt and mix, pour on a bag of sand.

[Davor]

You are simply lacking a lot thickness. Each target is characterised by its conductivity, but also its skin (effect) thickness. Lower conductivity - higher thickness. It is frequency dependent, but for practical purposes skin thickness of salt water is in a scale of meters.