On 9/28/2015 2:40 AM, Jeff wrote:

I agree that we are not all on the same page.

Then some of us much prefer to argue rather than discuss. Is there
anything about Waynes post you like? Are the facts more clear now at
least?


The situation is that with the ATU at the Tx end there are 2 mismatches
to consider.

1, the mismatch at the ATU output ( which hopefully has been adjusted by
the ATU to be small to keep the Tx happy.)

2. the mismatch between the antenna and the characteristic impedance of
the feeder.

Mismatch 2 causes the part of the signal to be reflected back down the
feeder towards the ATU which then re-reflects it back to the antenna,
which of course then re-reflects part of it back towards the ATU and so
on ad infinitum.

The ad infinitum can be expressed with a simple ratio. The reflections
constitute an infinite series that approaches a limit easily calculable.
Regardless, any incident energy reaching the antenna will be reflected
in the ratio determined by the impedance mismatch and measured by the
VSWR or the return loss ratio. It doesn't matter where the energy comes
from so talking bout infinite reflections serves no point when
discussing return loss ratio.


Of course each time the signal passes along the feeder it suffers the
loss due to the feeder.

As the amount of signal that is reflected at the antenna depends on the
SWR (or return loss) it is obvious that as the mismatch between the
feeder and antenna increases more of the power is subjected to multiple
trips along the feeder and so encounters more loss.

If you had lossless coax there would not be a problem, but even quite
low loss in the coax will cause significant loss when the mismatch
between the feeder and antenna gets a little high.

So getting the feeder impedance closer to that of the antenna can help.

Why can't the ATU also match the impedance of the cable eliminating
reflections there?

--

Rick

On 9/28/2015 12:03 AM, rickman wrote:
On 9/27/2015 10:39 PM, Jerry Stuckle wrote:
On 9/27/2015 9:46 PM, Wayne wrote:


"John S" wrote in message ...

On 9/27/2015 1:20 PM, Wayne wrote:


"rickman" wrote in message ...

On 9/27/2015 10:41 AM, kg7fu wrote:

Matching the antenna won't make the Return Loss go away but it will
make
the transmitter happy.

Can you explain this? I thought matching the antenna would *exactly*
make the return loss go away because it would eliminate the mismatch.

Not wanting to put words in his mouth....
I read that to mean that the high SWR between the ATU and the antenna
would remain, but the transmitter would be happy with the SWR on the
transmitter/ATU coax.


# Rick is correct. If the antenna (load) is matched to the line,
there is
# no return loss, hence no SWR. The ATU will be adjusted (hopefully) to
# make the transmitter operate properly with the impedance as seen at
the
# transmitter end of the line.

# Yes, the SWR due to mismatch of the antenna (load) and line will
remain.
# Even if the real part of your load impedance is matched to the
line, you
# will still have a high SWR if the reactance remains.

# Does this make sense?

Yes. That's what I was trying to say using SWR instead of return loss.
Return loss numbers get bigger with lower SWR.
For example: SWR 1:1 = infinite return loss.


Incorrect. Return loss increases with an increased SWR. An SWR of 1:1
has no return loss because there is no returned signal to lose. 100% of
the signal is radiated.

From LUNA web site regarding optical measurements which should be no
different from RF...


It "shouldn't be" - but optical measurements are handled differently
than electrical measurements. Fiber Optics have their own way of
measuring loss, reflection and refraction (which doesn't exist in
feedlines).

That's like applying electrician's color codes to electronics. They
both have color codes - but don't hook the electrician's black wire to
ground - or the transformer's green wires to safety ground.

--
==================
Remove the "x" from my email address
Jerry Stuckle

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

"Jerry Stuckle" wrote in message ...

On 9/27/2015 9:46 PM, Wayne wrote:


"John S" wrote in message ...

On 9/27/2015 1:20 PM, Wayne wrote:


"rickman" wrote in message ...

On 9/27/2015 10:41 AM, kg7fu wrote:

Matching the antenna won't make the Return Loss go away but it will
make
the transmitter happy.

Can you explain this? I thought matching the antenna would *exactly*
make the return loss go away because it would eliminate the mismatch.

Not wanting to put words in his mouth....
I read that to mean that the high SWR between the ATU and the antenna
would remain, but the transmitter would be happy with the SWR on the
transmitter/ATU coax.


# Rick is correct. If the antenna (load) is matched to the line, there is
# no return loss, hence no SWR. The ATU will be adjusted (hopefully) to
# make the transmitter operate properly with the impedance as seen at the
# transmitter end of the line.

# Yes, the SWR due to mismatch of the antenna (load) and line will remain.
# Even if the real part of your load impedance is matched to the line, you
# will still have a high SWR if the reactance remains.

# Does this make sense?

Yes. That's what I was trying to say using SWR instead of return loss.
Return loss numbers get bigger with lower SWR.
For example: SWR 1:1 = infinite return loss.


# Incorrect. Return loss increases with an increased SWR. An SWR of 1:1
# has no return loss because there is no returned signal to lose. 100% of
# the signal is radiated.

Return loss is the difference in dB between the forward power and reflected
power.
Less reflected makes a bigger difference and the return loss goes up.

I did a very quick Google and came up with this page that will calculate
SWR, return loss, and reflection coefficient.
Give it a try with SWR of 3, 2, and 1.

http://cgi.www.telestrian.co.uk/cgi-....co.uk/vswr.pl

In message , rickman
writes



Definition of Return Loss

In technical terms, RL is the ratio of the light reflected back from a
device under test, Pout, to the light launched into that device, Pin,
usually expressed as a negative number in dB.

RL = 10 log10(Pout/Pin)

Here is a link for a table of return loss and VSWR....

http://www.jampro.com/uploads/tech_d.../VSWRChart.pdf

It shows a higher return loss (assuming you mean magnitude since the
values are all negative) for lower VSWR.

I'm surprised to see negative quantities. For 50 years, I've always
understood the Return Loss Ratio (RLR) to be exactly what it says on the
tin, ie the ratio (in dB) of the LOSS (the attenuation) of the reflected
signal wrt the incident signal. This is a +ve quantity. Things are
already sufficiently confusing without having to start thinking in
unnecessary -ve figures!


--
Ian

"Ian Jackson" wrote in message ...

In message , rickman
writes



Definition of Return Loss

In technical terms, RL is the ratio of the light reflected back from a
device under test, Pout, to the light launched into that device, Pin,
usually expressed as a negative number in dB.

RL = 10 log10(Pout/Pin)

Here is a link for a table of return loss and VSWR....

http://www.jampro.com/uploads/tech_d.../VSWRChart.pdf

It shows a higher return loss (assuming you mean magnitude since the
values are all negative) for lower VSWR.


I'm surprised to see negative quantities. For 50 years, I've always
understood the Return Loss Ratio (RLR) to be exactly what it says on the
tin, ie the ratio (in dB) of the LOSS (the attenuation) of the reflected
signal wrt the incident signal. This is a +ve quantity. Things are
already sufficiently confusing without having to start thinking in
unnecessary -ve figures!

I think the table headings are using a dash, not a negative sign.
Return loss- dB

On 9/28/2015 10:47 AM, Ian Jackson wrote:
In message , rickman writes



Definition of Return Loss

In technical terms, RL is the ratio of the light reflected back from a
device under test, Pout, to the light launched into that device, Pin,
usually expressed as a negative number in dB.

RL = 10 log10(Pout/Pin)

Here is a link for a table of return loss and VSWR....

http://www.jampro.com/uploads/tech_d.../VSWRChart.pdf

It shows a higher return loss (assuming you mean magnitude since the
values are all negative) for lower VSWR.

I'm surprised to see negative quantities. For 50 years, I've always
understood the Return Loss Ratio (RLR) to be exactly what it says on the
tin, ie the ratio (in dB) of the LOSS (the attenuation) of the reflected
signal wrt the incident signal. This is a +ve quantity. Things are
already sufficiently confusing without having to start thinking in
unnecessary -ve figures!



I think you are correct. I think the confusion is the word *loss*. If
you have a positive *loss* number, the return signal is reduced. To have
a negative return loss number, you need to refer to *gain*.

For example, a return *loss* of 20dB is the same as a return *gain* of
-20dB.

On 9/28/2015 7:23 AM, Jeff wrote:

Why can't the ATU also match the impedance of the cable eliminating
reflections there?

The ATU is only in one location, if it is directly at the antenna feed
point the there is only 1 mismatch to tune out. If you put the ATU at
the Tx end and have a feeder between the ATU and the antenna then the
ATU can do nothing about the mismatch between the antenna and the
characteristic impedance of the feeder; all it can do is make whatever
impedance there is at the Tx end of the feeder acceptable for the Tx.

I wasn't refering to reflections at the antenna. I was referring to the
reflections from the ATU to cable interface. The ATU can match both the
transmitter and the cable, no?

--

Rick

On 9/28/2015 10:38 AM, Jerry Stuckle wrote:
On 9/28/2015 12:03 AM, rickman wrote:
On 9/27/2015 10:39 PM, Jerry Stuckle wrote:
On 9/27/2015 9:46 PM, Wayne wrote:


"John S" wrote in message ...

On 9/27/2015 1:20 PM, Wayne wrote:


"rickman" wrote in message ...

On 9/27/2015 10:41 AM, kg7fu wrote:

Matching the antenna won't make the Return Loss go away but it will
make
the transmitter happy.

Can you explain this? I thought matching the antenna would *exactly*
make the return loss go away because it would eliminate the mismatch.

Not wanting to put words in his mouth....
I read that to mean that the high SWR between the ATU and the antenna
would remain, but the transmitter would be happy with the SWR on the
transmitter/ATU coax.


# Rick is correct. If the antenna (load) is matched to the line,
there is
# no return loss, hence no SWR. The ATU will be adjusted (hopefully) to
# make the transmitter operate properly with the impedance as seen at
the
# transmitter end of the line.

# Yes, the SWR due to mismatch of the antenna (load) and line will
remain.
# Even if the real part of your load impedance is matched to the
line, you
# will still have a high SWR if the reactance remains.

# Does this make sense?

Yes. That's what I was trying to say using SWR instead of return loss.
Return loss numbers get bigger with lower SWR.
For example: SWR 1:1 = infinite return loss.


Incorrect. Return loss increases with an increased SWR. An SWR of 1:1
has no return loss because there is no returned signal to lose. 100% of
the signal is radiated.

From LUNA web site regarding optical measurements which should be no
different from RF...


It "shouldn't be" - but optical measurements are handled differently
than electrical measurements. Fiber Optics have their own way of
measuring loss, reflection and refraction (which doesn't exist in
feedlines).

That's like applying electrician's color codes to electronics. They
both have color codes - but don't hook the electrician's black wire to
ground - or the transformer's green wires to safety ground.

I thought you would claim optical was different. That's why I included
the VSWR vs return loss table link. You didn't comment on that.

--

Rick

On 9/28/2015 11:47 AM, Ian Jackson wrote:
In message , rickman writes



Definition of Return Loss

In technical terms, RL is the ratio of the light reflected back from a
device under test, Pout, to the light launched into that device, Pin,
usually expressed as a negative number in dB.

RL = 10 log10(Pout/Pin)

Here is a link for a table of return loss and VSWR....

http://www.jampro.com/uploads/tech_d.../VSWRChart.pdf

It shows a higher return loss (assuming you mean magnitude since the
values are all negative) for lower VSWR.

I'm surprised to see negative quantities. For 50 years, I've always
understood the Return Loss Ratio (RLR) to be exactly what it says on the
tin, ie the ratio (in dB) of the LOSS (the attenuation) of the reflected
signal wrt the incident signal. This is a +ve quantity. Things are
already sufficiently confusing without having to start thinking in
unnecessary -ve figures!

The ratio is not larger than one. So the log will be zero or less. In
dB the value will be negative for any reflection other than none.

--

Rick

On 9/28/2015 11:59 AM, Wayne wrote:


"Ian Jackson" wrote in message ...
In message , rickman writes



Definition of Return Loss

In technical terms, RL is the ratio of the light reflected back from
a device under test, Pout, to the light launched into that device,
Pin, usually expressed as a negative number in dB.

RL = 10 log10(Pout/Pin)

Here is a link for a table of return loss and VSWR....

http://www.jampro.com/uploads/tech_d.../VSWRChart.pdf

It shows a higher return loss (assuming you mean magnitude since the
values are all negative) for lower VSWR.


I'm surprised to see negative quantities. For 50 years, I've always
understood the Return Loss Ratio (RLR) to be exactly what it says on
the tin, ie the ratio (in dB) of the LOSS (the attenuation) of the
reflected signal wrt the incident signal. This is a +ve quantity.
Things are already sufficiently confusing without having to start
thinking in unnecessary -ve figures!

I think the table headings are using a dash, not a negative sign.
Return loss- dB

Look at the equation and you will understand. When the ratio is less
than one, the log is negative.

--

Rick