Eric, have you tried making a 2 Box PI ?

[Anonymous]

I thought you had mentioned the idea awhile back and wondered if you had tried it yet? While I'm waiting for the "Pulse Devil" to be introduced, I ordered Carl Morelands "Geotech PI" circuit board and thought it would be fun to break the receive path and add a separate coil. Since the receive coil is usually horizontal with the xmit coil in the veritcal position, I thought it might be interesting to put it in a faraday shield with a diode across the gap that would get shorted out during the transmit pulse. The idea being to cut down on coupling to the xmit loop and also mineralization in the ground. Is their any merit in doing this?

 

[Anonymous]

Hi Randy,
I did make a two coil PI many years ago, where there were two square coils about 2ft sq. mounted on a frame and separated by about 3ft. They were mounted in the same plane rather than at right angles. The idea seemed to work OK as a deep large object detector with little sensitivity to small objects or the ground. I never pursued it further though. As with a conventional PI, all the measurements are done in the off time, so there is no coupling between TX and RX to worry about. If you want to do a reactive measurement in the on time, then you would need to balance the coils by having them at right angles - but that is another ball game.
Eric.

 

[Anonymous]

i will like to try the two box Eric did mention...any idea where i can find the drawings to duplicate the machine???

 

[Anonymous]

I guess my train of thought for decoupling was to prevent the transmit field from inducing currents into the RX coil. What I think would also be interesting with the Faraday Shielded loop,would be to resonate it and tuning it from audio to 100 KHZ while sweeping a gold nugget to see if there would be a noticable differance (besides the change in BW due to the change in the coils Q).
Randy Seden