Question maybe Tom could help with, "EMI"

There is a long discussion on another forum about cures for EMI with the "F" series detectors. One of the methods being talked about is using the "Snap-Together Ferrite Choke Core" from Radio Shack and attaching it to coil cable. Another is using some EMI shielding tape ect. Maybe Tom could shed some light on this subject.



Edited 1 time(s). Last edit at 05/04/2010 09:03PM by iskirkra.

Most EMI enters the unit through the coil. Picked up from surrounding atmosphere. You obviously do not want to put any shield tape on the coil. Shielding the control box/head.......will produce minimal effect.
As far as attaching a ferrite choke core (magnet) around the coil cable... would suit no purpose...........as the cable is already shielded; rendering any additional external apparatus useless. . . . . . aside from the fact that EMI has already entered into the coil.

Thanks Tom for responding on this one, that makes good sense that EMI enters through the coil. I have even tried wrapping the entire contol box with layers of foil, just for the fun of it, and didn't help my EMI issues at all. When you have good areas to hunt and EMI is big problem you'll try just about anything. Thanks Randy

Interesting thoughts.
NASA-Tom Wrote:
-------------------------------------------------------
> Most EMI enters the unit through the coil. Picked
> up from surrounding atmosphere. You obviously do
> not want to put any shield tape on the coil.
> Shielding the control box/head.......will produce
> minimal effect.
> As far as attaching a ferrite choke core (magnet)
> around the coil cable... would suit no
> purpose...........as the cable is already
> shielded; rendering any additional external
> apparatus useless. . . . . . aside from the fact
> that EMI has already entered into the coil.

I think somebody said it, but what would seem to work the best would be an inline notch filter designed to pass only a very narrow bandwidth centered on the frequency the detector operates at. Notch filters can be designed for a very narrow pass range. Could be what prevents use of a notch filter is signal attenuation. There would have to be some loss through the filter. If they made the notch filter a user selectable feature, though, it could still be useful in situations where EMI amplitude makes detecting almost impossible. Now that I think about it though, at VLF frequencies, a notch filter might be a little on the bulky side. I think I just talked myself out of that idea.



Edited 2 time(s). Last edit at 05/06/2010 01:34AM by dgc.