Effect of the Earth's Magnetic Field, and Sunspot Activity?

[Wirechief]

Hello everyone, I am wondering how much of an effect that the Earth's Magnetic Field actually has on a PI detector? Also when the Sunspot activity is at it's peak will it have much effect on the PI detector? Is there any math formulas that are commonly used to figure into the designing of the PI to compensate for the effects of the above? Thanks and God Bless all. Wirechief.

 

[Eric Foster]

Hi Wirechief,

A good PI detector will filter out low frequency signal caused by swinging the coil in the earth's magnetic field. This is done by taking an early sample, then a late sample, and subtracting the two. The late sample occurs after most metal signals have decayed substantially, but the low frequencies in question are much the same amplitude on both samples.

There are stories to the contrary, but I have never been aware that sunspot activity affects PI metal detectors.

Eric.

 

[Wirechief]

I think I see now Eric. In other words the first sample and the late sample will cancell out the unwanted inteference when they are subtracted from each other. Since the unwanted interference has about the same amplitude on both samples you get close to zero. Thanks for the instruction Eric. I guess we will just have to ponder the sunspot thing. By the way I got that Beachscan in today I got from Ebay but I'm still waiting on the lower shaft from Staffordshire, it was a shipping issue but I can tell that it got checked out pretty good by customs. Looks to be a straight forward instrument. CU later Eric. John, Wirechief.

 

[Prospector Al]

Hi Wirechief,

As a Ham, you know that the 11-year sunspot cycle affects radio communications owing to the changes in the ionosphere. The magnetic field fluctuations are too small to affect metal detectors.

However, the moon is much closer than the sun. Furthermore, the moon maintains its position so that the same face is always turned toward the earth. In addition to causing the ocean tides, the moon causes "magnetic tides", which cause all the magnetic domains in the soil minerals to be oriented in a direction pointing toward the moon, when the moon is full.

Thus, at full moon, the magnetic susceptibility of the soil is enhanced, permitting a deeper penetration by the field from the transmitter coil.

Normally, the random orientation of the domains has to be overcome by the detector field. When the domains are pre-aligned by the moon's field, much less energy is extracted from the detector's field, which results in deeper penetration.

However, the polarity of the transmitter pulse has to be the same as the moon's field, otherwise, lesser penetration results.

Ft = Fm + Fc x (1-Exp (t/T) Where Ft = the total field; Fm is the moon's field and Fc is the field from the transmitter coil. t = the running time and T = the time constant of the transmitter coil, which is the ratio between its inductance and resistance.

It's obvious from the equation that for maximal performance Fm and Fc must have the same sign.

I am currently working on Moon-Enhanced Detector technology--stay tuned!

P. Al, NB6K

 

[Wirechief]

Hello again Al and good to get your feedback on this subject. Ok on the effects of sunspots on detectors but I never thought about the moon WOW! I wonder what percentage of the time that the polarity of the detector field is matching that of the moon? Thanks for the equations also Al and I hope you bring us some really interesting data on Moon Enhancing Technology. How did you learn of the effects of the Moon? Are you a physicist? Is there a textbook that a fellow can get that goes into this subject? Well I asked enough questions so I will be waiting on some more feedback on this interesting subject Al, CU later and 73 for now. Wirechief.

 

[Eric Foster]

Hi Prospector Al,

I have noticed that effect when hunting at full moon. I have developed it further and now mount a ferrite magnet in the centre of the search coil to align the domains. As you say, it is important to get the polarities matching for the steady magnet field, and the pulsed transmitter field. An added benefit is that the magnet sucks out any surface iron. Look out for an upcoming detector called the Werewolf.

Eric.