Question....wrong forum but smart people here....

[Anonymous]

This is not a PI question,but a detector question.I have a certain brand and was air testing it and I could air test a penny at 7" (air test done indoors laid flat and waving a coin)I could get a sound off at 7" with the yard stick.But if I waved the coin much faster it would sound off at 9" and the target ID meter would ID the coin by two more inches in depth.
What am I doing to the magnetic field that is allowing this faster wave of the coin to be detected further away.I couldnot swing the coil that fast but would try if I am getting two more inches of depth...lol..Just thought I could get some input and hope I gave enough detail.

 

[Anonymous]

I dunno for sure, but i think that some detectors need to be wung fast to achieve optimum depth. They were older models though.

 

[Anonymous]

No disrespect to you Rick, but we try to keep it PI oriented. They are plenty of smart people on the other forums that could answer that question. I

 

[Anonymous]

on the Metal Detecting Equip forum. Lots of good people over there with techincal backgrounds. Your question should get a good thread going that I would be interested in reading also.
Tom

 

[Anonymous]

Hi Rick,
The reason you may see a depth increase by speeding up the movement of the coin has to do with the filter design of the detector.
On a VLF, the filters are calculated and built to reduce the ground signal while allowing a target signal to pass. This means that the filters are designed to perform at a certain sweep speed for maximum results. This may mean the ideal sweep speed may be a range of speeds and not just one specific sweep speed.
Generally, the design is set by the engineer for the desired results he wants to obtain. By raising the lower cutoff frequency, better ground signal reduction is obtained. However, this will also cause the condition you experience whereby sweeping slower may result in a loss of depth.
On a PI, the autotune feature does something similar since it is really a 1 filter machine. Actually, it is a multiple filter detector but the lower frequency cutoff filters are what are counted.
As for a PI, there is a greater tendency to reduce the higher or upper cutoff frequency to reduce noise. VLF's are not effected as seriously, so the upper frequency cutoff may be higher, thus allowing a faster sweep speed.
In other words, a VLF coil may be able to be moved faster and obtain better results. However, this depends upon the VLF and doesn't necessarily hold true for all.
A signal on a PI may peak at a certain sweep speed and then experience a reduction in depth if the coil is moved faster. This peak will most likely be obvious and will shift a little depending upon the autotune setting. Obviously, with the autotune speed at minimum, the peak will be negligable, but it can show up as the autotune speed is increased. Again, this is dependent upon the rest of the filtering involved that sets the upper cutoff frequency. This is what can determine the fastest speed allowed. These same filters reduce the noise pulses and smoothes them out.
Reg