Owen Duffy wrote:
On Sat, 8 Oct 2005 21:36:59 +0000 (UTC), "Reg Edwards"
wrote:


"Owen Duffy" wrote in message
.. .
On Sat, 08 Oct 2005 12:53:11 GMT, "Lee"

wrote:


Doesn`t work with a magloop!!!.....thanks anyway.

Why is that?

Owen

==========================
Because there is only one phase - that which corresponds to the motor
driving voltage.

Call me thick, I still don't understand why you can't sample the RF V
and I and feed them to a phase detector to provide an indication of
whether to adjust the capacitor up or down to achieve resonance (V in
phase with I).

Owen
--
Hi Owen, Of course you can sample the RF-V and I and use it to
adjust the capacitor via the motor control circuits. The motor driving
voltage is DC, and I don't understand the inferences in this example.
Automatic antenna tuners work on this principle, and work well.
Gary N4AST

Doesn`t work with a magloop!!!.....thanks anyway.

Why is that?

==========================
Because there is only one phase - that which corresponds to the
motor
driving voltage.
----
Reg.

======================================

Automatic Antenna Tuners and Magloops.

All ATUs work on the principle of adjusting tuning components such
that the load presented to the transmitter has a reflection
coefficient of RC = 0+j0 ohms. When mismatched the RC has both
magnitude and phase.

So there must be two L and/or C variables. That's why there are always
at least two knobs on the front of a manual tuner. Or, when
automatic, two electric motors. Or a set of relays which accomplish
the same tasks.

In the case of a T-network the variable components are usually a pair
of reversible motor-driven capacitors.

There is always a reflexion coefficient bridge which is at balance
when the transmitter load is simultaneously R = 50 and jX = 0. Or
impedance Magnitude = 50 and Phase = zero.

The RC bridge circuit is similar to the so-called SWR bridge except
that there are TWO voltage outputs - proportional to magnitude and
phase of the RC. Output voltages are amplified to drive the
reversible capacitor motors or operate the set of relays. The motors
go backwards and forwards and react with each other similar to what a
human operator does. When Z Magnitude = 50 and Phase Angle = zero, or
sufficiently near, motors stop and the green LED comes on.

Now, in the case of a magloop there is only one variable - the tuning
capacitor. The other component involved with the tune-up process is
FIXED. It is the diameter of the small coupling loop inside the main
loop which is fixed.

The small coupling loop, in conjunction with the main loop, behaves as
the single-turn primary winding of an impedance matching transformer.

The main loop, when at resonance, has a very low purely resistive
impedance, the sum of the radiation and loss resistances.

The effective turns-ratio of the transformer is approximately
proportional to the ratio of the areas enclosed by the two loops. It
so happens that when the diameter of the coupling loop is approx 1/5th
of the main loop diameter, the impedance looking into the coupling
loop is 50 ohms. If a 75-ohm feedline is used then the coupling loop
needs to be a little larger.

A nice property of a magloop is that an impedance match is
approximately independent of frequency. When changing bands it is not
necessary to change the diameter of the coupling loop even if could
easily be adjusted.

It can now be seen why the conventional ATU cannot be used with
magloops. What is needed is something which searches for minimum loop
impedance, or zero phase angle, as the tuning capacitor is varied. It
then stops.

Any ideas?
----
Reg, G4FGQ

On Sun, 9 Oct 2005 01:31:54 +0000 (UTC), "Reg Edwards"
wrote:

magloops. What is needed is something which searches for minimum loop
impedance, or zero phase angle, as the tuning capacitor is varied. It
then stops.

Any ideas?
----
Reg, G4FGQ

Isn't that what I described, a control system that samples RF V and I
at the antenna end of the transmission line, and uses that to control
the direction of the capacitor drive motor to send it to the point
where the phase difference is zero?

Yes, I am aware that is only adjusting the reactance of the load
presented, but yes, I was aware the R component doesn't vary over a
very wide range over the loop's operating frequency range, and that if
X was tamed, the line losses would be acceptable.

Owen
--

"Owen Duffy" wrote in message
...
On Sat, 08 Oct 2005 06:26:31 GMT, "Lee"
wrote:

To continue the saga......
snip

Assuming it is a permag motor, reduce the motor voltage... add a
current limited driver to limit the torque, an electronic shear pin if
you like... except it doesn't shear.

Yes, good idea......i`ll look into that.

I am assuming that you are trying to tune the reactance out, to
achieve an acceptable VSWR on the line to the ATU/transceiver

An ATU does not work too well with a magloop as the magloop has its own
tuning capacitor (ATU) built in all that happens is that the antenna and
feed are tuned as one....unless i misunderstand your comment!!!.

.. Have
you considered automating the capacitor drive. You could build a phase
detector (between V and I at the antenna input) as a sensor to control
the motor drive.

Yes, but that is a bit too involved when pulse width modulation will do the
job, albeit, manually.....good thought tho`......

Thanks for the input ....

Lee.........G6ZSG.....



Owen
--

"Cecil Moore" wrote in message
t...
Lee wrote:
Seriously, any ideas to slow the tuning rate will be most welcome .

What's wrong with a gear-head motor? I have some in my junk box.

Wish it was in my junkbox!!! ;-)

Lee....G6ZSG......

--
73, Cecil http://www.qsl.net/w5dxp

"Owen Duffy" wrote in message
...
On Sat, 8 Oct 2005 21:36:59 +0000 (UTC), "Reg Edwards"
wrote:


"Owen Duffy" wrote in message
.. .
On Sat, 08 Oct 2005 12:53:11 GMT, "Lee"

wrote:


Doesn`t work with a magloop!!!.....thanks anyway.

Why is that?

Owen

==========================
Because there is only one phase - that which corresponds to the motor
driving voltage.

Call me thick, I still don't understand why you can't sample the RF V
and I and feed them to a phase detector to provide an indication of
whether to adjust the capacitor up or down to achieve resonance (V in
phase with I).

Owen
--

No doubt you can Owen, but that is a little beyond my present technical
learning curve unfortunately.....but i`ll get there eventually, i`m learning
more as i post!!!.

Thanks.

Lee.....G6ZSG....

Reg Edwards wrote:

It can now be seen why the conventional ATU cannot be used with
magloops. What is needed is something which searches for minimum loop
impedance, or zero phase angle, as the tuning capacitor is varied. It
then stops.

Any ideas?

There was an article in RadCom some years ago describing an auto-tuning
Top Band vertical, which used a simple inline phase detector and a
little DC tuning motor. The phase detector is nothing complicated - it's
very like a toroid-type SWR bridge rearranged components - but there
was a lot of practical information about what's necessary for RF
shielding and decoupling.

The whole thing should work equally well for a magloop, since the
electronics don't care what kind of antenna it actually is.

The article was by Tim Forrester, G4WIM, and was reprinted in G4LQI's
'HF Antenna Collection' book... my copy of which is unfortunately in
another country.


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

There was an article in RadCom some years ago describing an
auto-tuning
Top Band vertical, which used a simple inline phase detector and a
little DC tuning motor.

==================================
Ian,

A magloop is an altogether different kettle of fish to a top-band
vertical. For a start, the Q of a magloop is in the order of 1000.
For a top-band vertical it may be about 50. For most antennas it is
about 10.

What I would like to know is has anybody ever made an automatic tuner
which works with a magloop. Or has manufactured one for sale?

By the way, thanks for the Teslar papers although I am unable to run
the programs.
----
Reg.

Reg Edwards wrote:

There was an article in RadCom some years ago describing an
auto-tuning
Top Band vertical, which used a simple inline phase detector and a
little DC tuning motor.

==================================
Ian,

A magloop is an altogether different kettle of fish to a top-band
vertical. For a start, the Q of a magloop is in the order of 1000.
For a top-band vertical it may be about 50. For most antennas it is
about 10.

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.

The overall gain around the servo loop will be the product of the
antenna Q, the mechanical gear ratios and the voltage gain in the
electronics. The last of these can be adjusted with a single pot. If you
have a higher antenna Q, you simply need less voltage gain.

What I would like to know is has anybody ever made an automatic tuner
which works with a magloop. Or has manufactured one for sale?

Don't know, never looked.

By the way, thanks for the Teslar papers although I am unable to run
the programs.

(I only downloaded the program for coupled inductors, but haven't
studied it yet. It ran OK, after having extracted all of its files into
a real directory; it won't run from inside the .zip 'directory'.)


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

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?
----
Regards, Reg, G4FGQ