Is there really an advantage to a DD coil????

[Jason in Enid]

Your accessment of how FBS (and FBS2) works are not quite correct. If you'd like to read the best explanation of how it really works, check out this post on findmall.
About that multi-frequency Thang.

His description of DD coils is wrong also. That's what happens when you copy from a website instead actually KNOWING what happens. The way he described the coil would be dead on one side. Depending on the detector, DD coils either have 2 sets of opposed windings, or they have a single set and the detector flips their roles back and forth between xmit and receive.

 

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[Jackalope]

*** Your accessment of how FBS (and FBS2) works are not quite correct. ***

Yes, you are correct. The three channels, as I understand it, are able to offset from the harmonic by a small amount (+/- 10%). That is the purpose of the noise cancel - to find a channel within that 20% range that is quiet. When it comes to processing, there are only two frequencies used (the third is for ground) and processed by the E-Trac. The low freq runs about 3.125kHz and the high freq used runs about 25kHz (give or take +/-10%). Any other freqs transmitted are harmonics and not used, even if the advertising says there are 27 transmitted (which is sorta correct) only two are actually processed.

The CTX3030 may be different, but I doubt it.