Figure eight Rx coil

[green]

I attached this chart to a reply in another thread to show the benefit of sampling with a lower delay. Coil(Rx, two eight inch diameter round coils side by side, opposite phase)(Tx oval surrounding Rx). Targets were swung from a pendulum over the stationary coil. Looks like coil can't see the 25x25mm target past 18 inches. A figure eight coil cancels noise, could it be it cancels the 25x25mm target past 18 inches or am I missing something?

[green]

I attached this chart to a reply in another thread to show the benefit of sampling with a lower delay. Coil(Rx, two eight inch diameter round coils side by side, opposite phase)(Tx oval surrounding Rx). Targets were swung from a pendulum over the stationary coil. Looks like coil can't see the 25x25mm target past 18 inches. A figure eight coil cancels noise, could it be it cancels the 25x25mm target past 18 inches or am I missing something?

Tried a couple tests to try and learn something. Made three targets of aluminum foil. 2x2 inches(1 layer), 1x2 inch piece folded once for a 1x1 inch(2layers), 1x1 inch piece folded twice for a .5x.5 inch(4 layers). Tests I've done in the past suggested, reducing length of square foil by half should reduce TC by half. Doubling layers should double TC. The three targets should have the same TC and they were close. Used the PI detector I've been playing with for the testing instead of the bench tester. Panel meter, reading integrator out doesn't have enough resolution(1mv) to see what is happening at 18 inches. The detector has another stage capacitor coupled with a gain around 15 before the threshold detector that I can't record(needs motion) I got 3.7usec for 1x1 inch 2 layer vs 2.7usec for the 25x25mm 2 layer target I tested before. Don't know why. I probably used the bench circuit with a different coil for the earlier tests. I have compared different amplifiers and coils in the past with the target TC being the same. Retested the 1x1 inch 2 layer and the 25x25mm 2 layer from earlier test, both tested close to 3.7usec today with the PI used as the tester. I think the temperature is probably a lot colder today but question if that would cause the difference. IDMD states reducing target size in half should reduce signal strength to 1/8. With the TC being the same was thinking my test should come close and it did so at least something made sense. I'll see if I can determine why the TC changed. Might explain why the detection differences at 6, 10 and 14usec delay are closer than I thought they should be.