Excal coil compatibility and phasing

[bklein]

I am installing a variety of coils on two excels - one an excel 2 and another a sword.
I see differences in how each coil behaves with each detector.
Is this pointing to a fault in one of the detectors or is it typical?
Also it is interesting how behavior changes depending on the phasing of the tx and rx coils - can someone explain what is happening here in each case?
If rx is wrong you don't hear anything, if tx is wrong an iron target nulls at the center of the coil.

[bklein]

Rx and tx were intermixed on one detector so one of each would go to tx and rx. This actually gives a threshold sound and lousy target detection. All coils working basically the same although the Sword pod may be runnung a bit more sensitive.
The NEL Attack coil I got used off eshmay detects large iron but not coins. Seems bad. Says on it “for Minelab” - maybe another detector type?

[bklein]

NEL works too, had wiring wrong on it. Drrrrrr....
If one each RX/TX go to TX coil and RX coil you can get a threshold and iron detect but no coin detect.
I did the same thing wrong several times but luckily didn't believe trust myself and measured with a meter again and sure enough I had things mixed up.