VLF without IB

[FrancoItaly]

This is my idea, the RX coil is coplanar to the TX coil, then the RX signal is maximum. If we connect the input of an operazional with the signal of the RX coil and with a signal of equal amplitude but out of phase by 180 degrees we can obtain a reduction of the signal and we can continue this procedure with other stages. In this way we can simplify the construction of the head, which can also be large and the sensitivity is uniform and there are no "dead zones".
Is there something wrong?

[Davor]

In principle this can do, but... every nonlinearity will spoil balance, so at the end you'll end up with poorly balanced design. Since you already go for a coplanar design, why not going all the way and achieve balance by geometric means?

[Carl-NC]

One problem is that the cancellation is done in active circuitry; swap loops and the cancellation has to be recalibrated. Theoretically done with an automagical circuit, but difficult. Second is what Davor mentions, non-linearity will kill the depth of the null. You will always get a better null using the magnetic field rather than a drive signal.

[golfnut]

My view is your looking at doing Phase null (as well as an amplitude null)

The Phase null has no bandwidth and may jump either side of cancellation and saturate the Rx preamp in use


A PLL well designed could do it - the problem is there will be more than one signal here, ie, your main coupled signal in air, the ground signal and target signal phases.

The pll would remove the static air signal to zero, but when you approach the ground it my track the gound signal out and leak the static coupled signal...


If the closed loop bandwidth of the PLL was really narrow it would not track out fast changing things like target signal, or rapidly changing ground signals from a lively bouncy sweep.

So may work then - cant see the advantage in use?


With a wound induction null it has a small finite bandwidth so the amplitude null is not phase' sensitive and behaves well in use

[golfnut]

sorry carl stomped in at same time, typed over a while watching tv

[FrancoItaly]

I'm not an engineer, and maybe I simplify it too much, but the cancellation must be done only once and of course the head must be locked with resin and the ground exclude and discrimination can be made in the traditional way.