Centre Tapped Coils

[Math]

Hi, what are the pros and cons of centre tapped coils?
They seem to be commonplace in early IB non motion designs
Some having both TX and RX centre tapped but not so widely used thesedays..
Teknetics T2 has centre tapped TX ..Fisher F75 doesnt?

Thanks

[Altra]

With a center tapped Tx coil you can effectively double your peak to peak output voltage. I noticed some of the early TR's with center tapped coils used no shielding. I bought a Fisher M-Scope years ago at a flea market for $10. It was a model used by utilities and workers locating buried pipes and markers. It had center tapped Tx and RX coils with the same number of turns and no shielding. It was a double D configuration. I guess with a differential Rx pre-amp and careful tuning the capacitative(sp?) coupling was minimized? These detectors were not that sensitive compared to modern models, so they got away with no shielding and common cable. Probably not used much today because of the extra conductors in the cable. You might need 5 to 6 conductors vs 4. Most quality vlf detectors are using dual coax cable, similar to s-video. Minelab has even replaced the tin plated shielding with nylon coated magnet wire. Center tapped co-planer coils are also harder to null, double D not so bad. The Makro Racer uses a center tapped Tx coil to boost the signal from 5v to over 10v.

[Math]

Hi Altra thanks very much, ive always been a bit confused with centre tapped coils
A CT coil is 2 inductors in parallel? So when you say double the voltage thats with
double the current ..due to half the inductance and resistance of a single coil of the
same specs? Ive been thinking about this..
For a 2mh CT coil.. is equivalent to approx 1mh single coil for same current flow?
Say 20turns total to make the CT 2mh.. and say 15 for the 1mh single coil
The CT design has advantage of less turns so lower resistance per half
and would make a higher Q coil? good for TX.. not sure this is better for RX?
Which one would have less capacitance and higher resonant frequency.. and then
when you add the RX in a mutual arrangement.. which setup has the higher
resonance then? I should do some experiments..

Good points about the lack of shielding and extra RX tuning for the old CT coils and
re the cables.. Minelab have changed to magnet wire for shielding in the cables
and for the coil shield?

Thanks