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Shielding

A

Anonymous

Guest
Eric I had a thought last night about your detectors.
Is the cable from the coil primarily the shield connected to the metal case of the detector or is it isolated from it. Just wondering because I have a plastic box my pi board is mounted in. I have used aluminum duct tape inside the box and am wondering if I should connect it to ground of the electronics or not. for noise reduction.
Thanks
Ray(NM)
 
Hi Ray,
The braid of the coax is connected to any internal metal shielding that the detector electronics may have. It is better to ground any internal metalwork, because if it is just left floating, the noise pickup can be increased.
Some plastic boxes come with a deposited coating of conducted paint inside. This gives good shielding for r.f., but again, it must be grounded to the electronics ground and coax braid.
Eric.
 
Thanks Eric just what I figured. <img src="/metal/html/smile.gif" border=0 width=15 height=15 alt=":)">
 
Eric,
I built one of Gary's PI detectors and have made many shape and size coils that have tought me alot. I 've been shielding with foil and it works but I thinks it could be alot quieter. Would using Nickel spray help with the increased noise I get the wetter the sand? Also, do you have any shematics of a depth gauge for a PI? I can pick up a penny 2-3 ft down on the wet sand. I seem to have to ajust alot when moving from dry to wet sand here in Florida. Any advice would be appreciated. Joe
 
Hi Joe,
Any shielding will not prevent the effects of moving from dry to wet sand, or changes in the salt content on different parts or the beach. If it did, then the sensitivity of the detector would be very poor for metals. The shielding has to be sufficient to prevent the strong false responses that you would get from variations in the capacitance between the coil and the ground. If you are using foil, then that is about as good as you can get. Conductive paints are considerably less conductive than foil, and the shielding effect will be less, although possibly still adequate.
I have seen Gary's detector mentioned on other forums, but haven't looked at the details. You say that a lot of adjustment is necessary, so I assume that it is not a self adjusting motion type circuit. A motion circuit is the best type for beach use, which largely overcomes the problems you mention.
Eric.
 
Eric,
Thanks for the info. Always looking to improve what I have. HH Joe
 
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