On Mon, 10 Oct 2005 14:20:09 GMT, Cecil Moore wrote:

....
I don't know much about small loops. Modern transceivers,
like my IC-706, have such good protection circuitry that
it can be tuned into any load at full power. Is there
....

I know it is common practice to tune screwdrivers for max power out
from IC706s (tuning for "maximum smoke"), but is that good for the
tuner?

Perhaps that is why Icom incorporated low power tuning of its system
tuners. The AH4 actually presents a very limited range of Z to the
radio, it effectively introduces a small attenuator at the tuner input
when tuning. So the radio is limited to around 10W, the Z excursions
are limited, and the tuner relays operate at quite low power. I wonder
what they know that we don't?

Perhaps it is why Kenwood drops carrier before each relay operation in
autotuning the TS2000 internal tuner. (Some of their earlier models
have a reputation for tuner relay failure.)

It may be that tuning screwdrivers under full power isn't detrimental
(I just don't know), but it is probably not safe to generalise.

Owen
--

Cecil Moore wrote:
Reg Edwards wrote:
So we need something different from and more sophisticated than the
conventional automatic tuner with its relatively simple magnitude and
phase-searching abilities.

I'll believe it when I see one which works.

Reg, I just opened up my 2006 MFJ catalog. They have
an "Automatic LoopTuner(TM)", the 300w MFJ-937. It's
designed for approximately 1/10WL loops.
--
73, Cecil, http://www.qsl.net/w5dxp
Hi Cecil, Looking at the MFJ site and trying to reverse engineer the
loop tuners they sell...They monitor the loop current to get resonance,
tune for maximum. Then they have an "L" network to match 50 ohms.
They have a Butterfly style Cap. for HV., and monitor the current as it
is adjusted. Have a 50 ohm cross needle swr bridge to detect a 50 ohm
match, for their matching control. I assume their "auto loop tuner"
looks at the same stuff.
Gary N4AST

Owen Duffy wrote:
I know it is common practice to tune screwdrivers for max power out
from IC706s (tuning for "maximum smoke"), but is that good for the
tuner?

The SG-230 seems to handle 100 watts just fine. It is
interesting to listen to an autotuner tune up a transmitter
equipped with foldback. Clickidy-Click, the signal goes from
S5 to S9. If the foldback circuitry failed, then there would
probably be a bad outcome.

Assuming foldback and reflected power not invading the remote
tuner, I don't see why any harm would be done. 'Course, I'm
suffering from macular degeneration.
--
73, Cecil http://www.qsl.net/w5dxp

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