Eric....8 foot coils

[Anonymous]

Eric, did you produce a 8 or even 10 foot wide P.I. coil about 12 years back. Long Tom,Big Tom or similar sticks in my mind. If so what was the situation re sensitivity to smaller items. If I put an 8 x 3 on an old non-motion P.I. it still picks up fist size objects. VLF/I.B./T.R.'s seem to drop sensitivity rapidly, P.I.'s don't seem to or is it that the sensitivity is related to the smallest width of my coil,in this case 3 feet ?
Trying to achieve fair depth but only respond to targets 6 inches square and above.
Many thanks if you can help.

 

[Anonymous]

Hi Brian,
Yes, I did make a rectangular coil called Long Tom. It used to be sold as a kit to make it easier to send through the post. Rectangular coils are useful if you want rapid and thorough ground coverage, but the sensitivity to small objects obviously lessens. I have found that a three to one ratio of the sides is best; so 8in x 24in if you still want small objects, going to 24in x 72in or bigger, if you want less sensitivity to small items, greater depth and coverage.
What old PI detector do you have? The transmitter characteristics and pulse delay also have a considerable effect on performance.
Eric.

 

[Anonymous]

We have a Pulsedeck (mk3 ?),and an old deepscan which was altered so that large coils could be fitted (but lost VCO as a result). The intention is to cover very large areas in the old Soviet Union with very little rubbish but hope to avoid what there is by using a size that will give no response to a coke can,or smaller sized object.
Re ratio's I had great success on the beach in the good old days with a 3 foot x 9" which held in front cleaned the beach out with no worry about sweep or overlap. Wife did get annoyed at trundling behind pinpointing/discriminating/digging...can't understand why !