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figure 8 coil

A

Anonymous

Guest
Eric how do figure 8 coils compare with dd`s or mono`s I have a very noisey beach area I want to detect with my sd a lot of electrical interference,if we wound one what size should it be I was thinking 30-35cm [12-14ins]??
Regards
kris
 
Hi Kris,
They do not give as good a range as monos but are probably near to a DD. A good starting point would be a 16 x 8in or maybe 20 x 10in. A point to bear in mind is that on a horizontal coin or ring, the signal will null in the middle of the coil. Best to pinpoint by using just the front half. There is always a trade off <IMG SRC="/forums/images/smile.gif" BORDER=0 ALT=":)">
Eric.
 
Hi Eric,
the figure 8 is supposed to reduce electrical noise, but does this design have an effect on the ground response? In other words, would it reduce any of the ground signal that is common with a mono coil?
Thanks,
Reg
 
Hi Reg,
Tonight must be brainstorming night with posts and emails <IMG SRC="/forums/images/smile.gif" BORDER=0 ALT=":)"> Unfortunately the ground response is not reduced like the noise. The noise has the same polarity in each winding, which being connected in antiphase, cancels out. On transmit, however, each half of the winding transmits an opposite phase of TX signal. The RX phase of the signal from the ground is also opposite in each half, which because of the reverse connection of the coils, ends up by adding.
Eric.
 
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