On Mon, 10 Oct 2005 08:18:35 +0100, Ian White G/GM3SEK
wrote:

Reg Edwards wrote:

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

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Frequency is selected by the receiver, not the transmitter.

The transmitter is OFF when I do it manually and I tune for maximum
noise in the receiver. How do YOU do it? smiley

I freely admit, I've never touched the things... just trying to be
helpful :-)

But what do you think "maximum noise" means? You hope it's going to mean
maximum field strength when you come to transmit, but what does that
actually mean in terms of loop tuning conditions?


If I can't do it when the transmitter is ON then neither can an
automatic ATU. It would have to be more clever than I am.

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...
not abandon the idea.

First of all, somebody needs to build a phase detector for an existing
manually tuned loop, and see what results it gives.

Ian, Reg, I don't for a moment think automation of a loop tuner is
trivial, but I don't think it is impractical with modern processor
control techniques. For a practical solution, it will probably need
some king of position sense from which to derive end limits and
velocity for implementing a second order control loop.

It is probably a lot like autotuning a PA tank (and that was done in
closed loop linear systems decades ago), except that the loop Q is
probably much higher and the tuning range wider. The same problems
will be encountered in finding the true resonance where phase changes
very quickly from a large positive value to a large negative value or
vice versa depending on the direction of tuning.

It would be interesting Reg, just the install an SWR meter (this is
not a windup!) at your magloop, shut your eyes and tune it up on rx as
you describe, then see whether is is close to minimum SWR )which will
probably be at or very near zero reactance) on tx.

To some extent, the tuner algorithms will be simpler than for a two to
n variable tuner (many autotuners vary more than two components, they
may switch in an autotransformer, or change from L to PI or PI-L
configuration).

I am more interested to hear from someone who says it can't be done,
what they tried that didn't work.

A remote autotuner could be just the thing that makes a magloop a very
attractive, small, frequency versatile antenna (well, for those who
don't have the antenna in the shack or very long arms).

Owen
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