K7ITM wrote:
The Smith chart, to me, remains a very valuable _visualization_ tool.

Here's a recent posting of mine from eHam.net:

someone wrote: There are very few people out there that
use the Smith Chart.

I'm not suggesting that they actually use a Smith Chart - just that they
learn how to use one and keep the Smith Chart in their heads as a
conceptual tool. With a conceptual image of a Smith Chart in their
heads, they not only know what the input and output impedances are but
also the path the impedance took to get from one point to another. Did
the SWR spiral cross the 50 ohm circle or the 1/50 mho circle during its
transition? If so, matching to 50 ohms is a one component piece of cake.
--
73, Cecil, IEEE, OOTC, http://www.w5dxp.com

On May 21, 11:43*am, Jeff Liebermann wrote:
On Thu, 21 May 2009 07:28:25 -0700 (PDT), ve2pid
wrote:



Hi to all,

Just got my new ATU. The specs mentionned:

Tunes 6 to 600 ohms (about 10:1 SWR range). 16 to 150 on 6M (about
3:1)

It sems that this is the standardized (?) way to mention
specifications...

But, since impedances have both a resistive and reactive compoment,
doses it means 6 to 600 Ohms "resistive"?

For example , if Z= 500-J800 ohm, is it 'tunable'? I have a doubt
because the impedance could also mean sqrt(500^2+800^2)=943,4 Ohms..

Thanks de Pierre

Well, a little Googleing found the missing maker and model number.
It's obviously made by LDG but which product?
http://www.ldgelectronics.com
The spec sheets aren't any more useful. *I'm also rather suspicious
because ALL their products, regardless of size or technology, have the
same specification.


That's because all their tuners have the same component values (L and
C) in the same basic tuner configuration (switched L). The various
models just have different power ratings (and I suppose the loss is
different) and different other features.

It's a fairly straightforward process (albeit tedious) to map out all
possible places on the smith chart that can be tuned to 50 ohms by
their tuners. Somewhere around I have some plots I did with matlab
for just that.

Basically, you can get close by knowing the minimum and maximum L and
C available. The step size (which is fairly even across the range...
they have L and C in the 1,2,4,8 sequence) determines how close you
can get to 50 ohms from some arbitrary load Z (assuming it's in
range).


The power limitations on a tuner are sort of complex (which is why you
don't see a lot of detail). There's the current through the L and C,
and the voltage on the C. There's no simple relationship between,
say, vswr and component voltage/current, since it depends on the
particular match configuration. What you can assume is that the
potential rise is proportional to the Q of the antenna and tuner
together. Since antenna Q is usually fairly low compared to tuner
components, you could probably get close by taking the ratio of the
antenna's reactive component to the resistive component. (short
verticals, notorious for high voltages in a tuning network, have high
reactance and small resistance..)

Impedance is the product of inductive and capacitive reactance in a AC
circuit

Resistance is the load in a DC circuit.

I think impedance has a different affect at different frequencies.....

Please correct me if I got all my theory wrong.

Rollie

On May 23, 5:32�pm, "Rollie" wrote:
Impedance is the product of inductive and capacitive reactance in a AC
circuit

Resistance is the load in a DC circuit.

I think impedance has a different affect at different frequencies.....

Please correct me if I got all my theory wrong.

Rollie

Simply put, impedance is frequency dependent, resistance is not.
Thats why it is hard to specify a resistance or impedance range for a
tuner. Our antennas are frequency dependent because a 50 ohm match
is required no matter what frequency we transmit.

Gary N4AST

On May 21, 10:28*am, ve2pid wrote:
Hi to all,

Just got my new ATU. The specs mentionned:

Tunes 6 to 600 ohms (about 10:1 SWR range). 16 to 150 on 6M (about
3:1)

It sems that this is the standardized (?) way to mention
specifications...

But, since impedances have both a resistive and reactive compoment,
doses it means 6 to 600 Ohms "resistive"?

For example , if Z= 500-J800 ohm, is it 'tunable'? I have a doubt
because the impedance could also mean sqrt(500^2+800^2)=943,4 Ohms..

Thanks de Pierre

FYI finally got the answer from LDG:
----
It's polar coordinates (as opposed to rectangular).

For example: 200 -j300 in rectangular would have a magnitude of 360 in
polar.

I think we were the first company to ever publish tuning specs for
autotuners
and I happen to choose polar that day, so that's what everyone else
uses now for
autotuners.

It's just an approximate number, but it gives you a rough idea of what
to
expect. If you find that your long wire (for example) has an impedance
of 2500
ohms (either measured or simulated), you can be pretty sure that our
tuner is
not going to tune it.

----
So, I deduct 600 Ohms could mean any impedance A+JB where sqrt
(A^2+b^2)=600. ;-) ........

In article
,
ve2pid wrote:


I think we were the first company to ever publish tuning specs for
autotuners
and I happen to choose polar that day, so that's what everyone else
uses now for
autotuners.


Unless you published your specs over 20 years ago, Motorola was the
first one to publish Tuning Range Specs, for their Second Generation
Autotuner, back when Bill Shielb was Chief Engineer for the MF/HF SSB
Engineering Group......

Most of the Modern Day Binary Lumped Constant AutoTuners are based on
his work at Motorola, which he brought out west, when he came to
Northern Radio Co., and then finally to Berlonix Corp. The SEA-1600
by SEA, (Stephens Engineering Assoc.) was a reverse engineered AutoTuner
based on Bills work, done my Mark Johnson and Bill Forgey at SEA, but
with a much improved Microprocessor Control algorithm, Phase and Power
Sensors, and spawned a long Series of SEA16xx Autotuners, of which the
SEA1612B was the most recognized, and the SGC Tuners were copies.

K7ITM wrote:

It would be good if they plotted the range on something like a Smith
chart. It should be done for different frequencies; it's rare indeed
for a tuner to be able to match the same range of impedances over its
frequency range. Some tuner topologies even have "holes" in their
coverage.

Exactly ! You will find here an example:
http://www.darc.de/distrikte/c/09/Claude/Z-Match.pdf

73 de Claude