Reg Edwards wrote:
Not fundamentally different - it only means the magloop tuning will
be
more sensitive. The servo will still try to drive the system to
resonance at zero phase angle.
=================================

Ian, what slightly worries me is -

(1) The resistive component of antenna input impedance, as measured at
the input of the small coupling loop, when the main loop is even only
slightly off-resonant, is altogether different from 50 ohms but is not
included in the bridge balancing process. The diameter of the coupling
loop is fixed. Yet magnitude and phase adjustments react upon each
other as is experienced by a human operator with two variable
controls.

(2) The coupling between the two loops is very loose. We are trying to
adjust the main loop exactly to resonance via a means which is very
insensitive to its resonant condition. Direct voltage and current
sampling connections to the main loop itself are impossible.

(3) We can imagine a situation where the impedance phase-angle is zero
at the measuremnt point, and the green LEDs light up, but which does
not correspond to exact resonance in the main loop. And exact
resonance matters with a magloop.

(4) Because the system is trying to reduce a phase angle to zero in
the presence of two unknowns, instability can result. We can imagine
the system continuously hopping about trying to find the zero.

As you can see, I have difficulty in describing what I think happens
circuitwise. But I shall be convinced only when somebody produces
something which WORKS reliably without human intervention.

It may be possible but where is it?

I see your point... but what do you actually tune for, when you do it
manually?



--
73 from Ian G/GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek