On Sat, 22 Nov 2003 08:11:49 +0100, "Meindert Sprang"
wrote:

"Gary Schafer" wrote in message
.. .
On Fri, 21 Nov 2003 20:12:32 +0100, "Meindert Sprang"

You obviously don't understand how this works. The combination of antenna
and feedline presents a certain impedance at the end of the feedline.
What
the tuner does is transform the 50 Ohm on the TX side to the impedance on
the feedline. And when this all matches, there is no SWR. Neither on the
TX
side of the tuner, nor on the feedline side.

Meindert
pe1grv



Wann bet? :)

Try it some time. Tune the tuner so there is no SWR at the
transmitter. Then place the SWR meter between the tuner and the
transmission line. You will still see the same SWR that you started
with!

Of course you will. That's because you put the SWR meter on a place where
the impedance is not 50 Ohm anymore. So now you have a mismatch between the
feedline and 50 Ohm directional coupler in the SWR meter.

Meindert



Then how do you know that there ISN't any reflected power there when
you tune as you say? What do YOU measure it with??

You are right about the impedance seen at that point being different
because of the reflection but the CHARACTERISTIC IMPEDANCE of the
line has NOT changed and that is the important point.

Here is something for you guys with Bird watt meters to do to prove to
yourself what happens with reflected power. Get out your little
manual that came with your Bird through line meter. If you don't have
one go on line and look. I think Bird has that manual online.

It will tell you how to determine how much power is delivered to the
load (antenna).

"The characteristic impedance of the coax line must be the same as
that of the Bird meter (50 ohms). Subtract the reflected power reading
you get from the forward power reading you get. That is the power
delivered to the load." This holds true for any load as long as your
line is a 50 ohm line.

Still don't believe? Try this. With no tuner in your transmission
line tune your radio to a frequency where you see a high SWR. It
doesn't matter what it is. 80 meters if you have it is a good place to
do this as antenna bandwidth is rather narrow there. You can do this
at any power level that your radio is comfortable with.

Hook up your antenna tuner in the coax line as I have described
before. Place your Watt meter between the transmitter and tuner. Tune
the tuner for minimum reflected power to the radio. Note the forward
power reading on the watt meter. Don't touch the power level on the
radio. Replace the watt meter with any SWR bridge you might have
around. Set the control on the SWR meter for full scale indication.
This will be so you can achieve the same power out for the next step.

Now place the watt meter between the tuner and the antenna. Turn on
the transmitter and be sure that the SWR bridge reads the same as it
did before. This tells you that you still have the same power out of
the transmitter and that the tuner is still matched to the radio.

Now look at the watt meter! If you have a 3:1 SWR on the antenna line
and you had set up the radio for 100 watts out at the radio previously
with the tuner in line, the watt meter at the antenna side will read
125 watts forward with 25 watts reflected!!

Now do as the Bird manual tells you: Subtract the reflected reading
from the forward reading. It should equal 100 watts. The same amount
of power that the transmitter is putting out.

All you doubting Larry's please try this and report back what you
find.

Then tell us why reflected power is not re-reflected back to the
antenna if you can. :)

Regards
Gary