Wayne wrote:
I was looking at a MFJ remote antenna tuner, and it is specified as being
able to match 12 to 1600 ohms.

What does that mean? At 12 ohms the SWR would be about 4.2:1 and at 1600
ohms a SWR of about 32:1.

If one started from 1600 ohms around a Smith chart, the circle would
intersect at the other side at about 0.64 ohms.

Likewise starting at 12 ohms and going halfway around the chart would end up
at 210 ohms, not 1600.

How does one use the specs if the antenna to be matched has a complex
impedance? Look at the internal tuner component ranges?

Those ranges of impedances are basically worthless.

Looking at the component ranges is probably the best, but most complex
way.

Some makers give half way usefull info with things like will tune
a minumum of X feet long at 160 M.

I have both a SGC and a LDG; the SGC is much better range wise.


--
Jim Pennino

wrote in message
...
Wayne wrote:
Those ranges of impedances are basically worthless.
I don't agree :-)
If I had to test such a tuner the first thing I would do
is put a pure resistor of those values and try to
match them accross the frequency and power range announced.
Measuring the insertion loss would be nice too.
Of course it is not the complete story but a good start.

"bilou" wrote in message ...


wrote in message
...
Wayne wrote:
Those ranges of impedances are basically worthless.
I don't agree :-)
If I had to test such a tuner the first thing I would do
is put a pure resistor of those values and try to
match them accross the frequency and power range announced.
Measuring the insertion loss would be nice too.
Of course it is not the complete story but a good start.

That's true, but I would like for the specs to give me an idea if I want to
buy it.

bilou wrote:

wrote in message
...
Wayne wrote:
Those ranges of impedances are basically worthless.
I don't agree :-)
If I had to test such a tuner the first thing I would do
is put a pure resistor of those values and try to
match them accross the frequency and power range announced.
Measuring the insertion loss would be nice too.
Of course it is not the complete story but a good start.

Which basically tells you nothing about the ability to match a complex
load.

I measured the impdance of a vertical to be well under the specified
limits of the LDG tuner I own. However, it fails to get a match on
160 M and 17 M.

The SGC tuner has no problems getting a match.



--
Jim Pennino

wrote in message
...
bilou wrote:

wrote in message
...
Wayne wrote:
Those ranges of impedances are basically worthless.
I don't agree :-)
If I had to test such a tuner the first thing I would do
is put a pure resistor of those values and try to
match them accross the frequency and power range announced.
Measuring the insertion loss would be nice too.
Of course it is not the complete story but a good start.

Which basically tells you nothing about the ability to match a complex
load.
Hello
You are absolutely right in fact a perfect ferrite transformer would be
better.
But an aerial must have a real impedance part to be of any use :-)
Specifications must be easy to verify.
Here it is the case.
How do you check the 0.1dB noise figure advocated by many LNB's ?
:-)

bilou wrote:

wrote in message
...
bilou wrote:

wrote in message
...
Wayne wrote:
Those ranges of impedances are basically worthless.
I don't agree :-)
If I had to test such a tuner the first thing I would do
is put a pure resistor of those values and try to
match them accross the frequency and power range announced.
Measuring the insertion loss would be nice too.
Of course it is not the complete story but a good start.

Which basically tells you nothing about the ability to match a complex
load.
Hello
You are absolutely right in fact a perfect ferrite transformer would be
better.

It is rather difficult for a ferrite transformer to convert a random
complex impedance to approximately 50 Ohm resistive, which is what
an autotuner does.

But an aerial must have a real impedance part to be of any use :-)

Which is why one uses an autotuner to convert the random complex impedance
to approximately 50 Ohm resistive.

Specifications must be easy to verify.

And life must be fair...

Here it is the case.
How do you check the 0.1dB noise figure advocated by many LNB's ?

With test equipment.


--
Jim Pennino