"Understanding P.I. Interference" (Book Exerpt).

[cjc]

20/ Understanding P.I. Interference
Having encouraged several dyed-in-the-wool VLF hunters to give the Dual Field a try, I

 

[don tyler]

Thanks for added info Clive, Don Tyler, Will be in Mexico, in a couple of weeks

 

[TheMarshall]

20/ Understanding P.I. Interference
Having encouraged several dyed-in-the-wool VLF hunters to give the Dual Field a try, I

 

[Eric Foster]

With a 20in diameter coil the sea water signal increases till you reach a depth of 30ft. where it then stays constant until you get within 30ft of the bottom, when it decreases again. When you reach the bottom, unless it is bare bedrock, the signal will not have fallen to the level you got at the surface. Say you have 10ft of water saturated sand on the bedrock, the signal will have roughly dropped to what it was 10ft below the surface.

In shallow water the detector will respond to waves or swell passing over the coil. A fast SAT speed will nullify this to some degree.

Eric.

 

[mikebg]

With a 20in diameter coil the sea water signal increases till you reach a depth of 30ft. where it then stays constant until you get within 30ft of the bottom, when it decreases again. When you reach the bottom, unless it is bare bedrock, the signal will not have fallen to the level you got at the surface. Say you have 10ft of water saturated sand on the bedrock, the signal will have roughly dropped to what it was 10ft below the surface.

In shallow water the detector will respond to waves or swell passing over the coil. A fast SAT speed will nullify this to some degree.

Eric.

Eric, at which frequency this measurement is made?
Oops, sorry, my question is in the frequency domain!
For the PI Technology Forum the question should be:
"At which sample delay this test is made?"
Mike-BG

 

[Eric Foster]

Hi Mike,

It would have been about 100uS delay. For deep diving detectors, short delays are not useable (at present) due to the strong water signal. Smaller coils improve things but anything less than 25uS delay is hard to use.

Eric.

 

[w6pea]

Thank you for posting this a Great Read

 

[acasto]

I finally got my head around most of this info.
Can someone explain, please?

" A fast SAT speed will nullify this to some degree: How is this adjusted?

I am using a Sea hunter MkII

Much gracias