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..)