Reg Edwards wrote:

"Ian White G/GM3SEK" wrote in
If we're not clever enough to build an automatic ATU for a magloop,
it's
a sign that there's something about magloops we still need to
know...
====================================

We are able to analyse and predict the behaviour of magloops to any
required degree of precision.

What is missing is how both a magnitude-searching and phase-searching
circuit of an automatic tuner works when denied access to the
magnitude-searching component.

Not necessarily... see later.

These paragraphs about a T-tuner are really a digression from this
topic, but worth a comment:

When manually adjusting a tuner it is obvious to the operator that the
controls INTERACT with each other. Both variable controls equally
affect both magnitude and phase. That much can be gleaned from
inspection of the circuitry.

For example, in the case of a T-tuner with two variable capacitors,
the operator cannot concentrate on one variable exclusively to the
other. He continually has to swap from one to the other and obtain a
balance by progressively closer approximations whilst keeping his eyes
on the co-called SWR meter.

An automatic tuner manages to complete the operation by varying both
controls simultaneously. But it is obvious from observation of what
the drive motors are doing, and the time taken to do it, that the
circuit is behaving just like a human operator. Occasionally the
motors even have to reverse and try again.

When denied access to either one of the two variable controls, the
automatic tuner doesn't know what to do next and would become lost.

There are actually three variable controls in a C-L-C T-tuner. For
minimum internal losses (mostly in the L) the inductance needs to finish
up at the smallest value that will allow the two Cs to achieve a match.
To do it right, there should be some stepping of the L, until it won't
match any more, and then a step back to the last set of values that did
match.

If the desired impedance magnitude is known to be 50 ohms and is
somehow inserted in the circuit, this is of little assistance to how
the circuit behaves because when the main loop is off-resonance the
actual resistive component is miles away from 50 ohms yet the
automatic tuner is obliged to do something about it.

Not sure what you mean here (that thing about "inserted in circuit"
wasn't anything I intended to suggest or imply).

Back to loops...

But without the
ability to vary the diameter of the coupling loop, as I say, it is
lost.

Hang on - who varies the diameter of the coupling loop in routine
operation? I thought we were only looking for something that would help
a correctly functioning loop to track up and down the band.... in other
words, to operate the tuning control for us.

Like Owen, I'd still be very interested to learn what "maximum noise" on
receive actually means in terms of R and X and/or phase on transmit.


I trust you are comfortably settling down in your new country. I have
spent happy years, in bits, working in Scotland. It is a most
civilised place.

It certainly is. I wish we were there all the time, but my wife and I
are still only spending about one week in two in our new home, because
the removal from England is still dragging on.

Apologies in advance, but I don't have a newsgroup feed in Scotland yet,
which means I'm liable to disappear suddenly in mid-conversa




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