SWR again.
 

....if already going into it, a little bit of history.
when the cows had bigger heads and the air was greener, there was no
such thing as coax. what we used was the ubiquitous ladder wire, with
an unknown impedance and with a frequency response depending on what
the Gods ate at lunch! the VSWR story was not invented yet.
What we did was one of two things: either tune the system for maximum
current in the line or else used a light bulb in conjunction with a
small light bulb and tuned for maximum brilliance. in neither case was
SWR involved in the mess.
the whole SWR uproar began after WW2 with the advent of coax and the
new fangled theories. that was also the time when all kind of
directional couplers came up.in due time a few wise guys developed all
kinds of theories on the subject, and manged to convey the impression
that SWR is king! nothing further from truth. what's really true is
that reflections can cause the apparent impedance at the network's
input to differ from Zo. SO WHAT? if you can adjust your matching
network between the transmitter and the line for a match what do you
care?
actually the hitch is that, with a high SWR on the line, the losses go
up. if the cable can take it, without melting no harm's done: whatever
remains will get radiated. this was the good pint of open feeders: the
losses were very low. an SWR fo 10 and more was insignificant from the
losses' point ov view.
Guys, leave it alone! Just make sure that the SWR is a reasonable
value, something that the transmitter can handle and leave it at that.
Saandy 4Z5KS





Reg Edwards wrote:
"Saandy wrote

you can't measure SWR.
=========================================

I am pleased you agree with me.

=========================================
You can CALCULATE the SWR using the formula.
=========================================

But of what use is the SWR it after you have calculated it?

To what transmission line does it apply? Where is it? What are the
locations of max-volts and min-volts? It does NOT apply to the line
between transmitter and antenna. I suggest it exists only in your
imagination. ;o)

It is the name of "SWR Meter" which leads to confusion,
misunderstandings and arguments. The name says the instrument does
something which it does not do. With the help of old-wives, novices
are led astray and are stuck with incorrect ideas about standing-waves
for the rest of the lives.

Just change the name to TLI (Transmitter Loading Indicator) which is
what it is and does very well. The true meaning and associations of
SWR will then emerge and all will be flooded with the light of reason.
----
Reg, G4FGQ.

SWR again.
 

....if already going into it, a little bit of history.
when the cows had bigger heads and the air was greener, there was no
such thing as coax. what we used was the ubiquitous ladder wire, with
an unknown impedance and with a frequency response depending on what
the Gods ate at lunch! the VSWR story was not invented yet.
What we did was one of two things: either tune the system for maximum
current in the line or else used a light bulb in conjunction with a
small light bulb and tuned for maximum brilliance. in neither case was
SWR involved in the mess.
the whole SWR uproar began after WW2 with the advent of coax and the
new fangled theories. that was also the time when all kind of
directional couplers came up.in due time a few wise guys developed all
kinds of theories on the subject, and manged to convey the impression
that SWR is king! nothing further from truth. what's really true is
that reflections can cause the apparent impedance at the network's
input to differ from Zo. SO WHAT? if you can adjust your matching
network between the transmitter and the line for a match what do you
care?
actually the hitch is that, with a high SWR on the line, the losses go
up. if the cable can take it, without melting no harm's done: whatever
remains will get radiated. this was the good pint of open feeders: the
losses were very low. an SWR fo 10 and more was insignificant from the
losses' point ov view.
Guys, leave it alone! Just make sure that the SWR is a reasonable
value, something that the transmitter can handle and leave it at that.
Saandy 4Z5KS





Reg Edwards wrote:
"Saandy wrote

you can't measure SWR.
=========================================

I am pleased you agree with me.

=========================================
You can CALCULATE the SWR using the formula.
=========================================

But of what use is the SWR it after you have calculated it?

To what transmission line does it apply? Where is it? What are the
locations of max-volts and min-volts? It does NOT apply to the line
between transmitter and antenna. I suggest it exists only in your
imagination. ;o)

It is the name of "SWR Meter" which leads to confusion,
misunderstandings and arguments. The name says the instrument does
something which it does not do. With the help of old-wives, novices
are led astray and are stuck with incorrect ideas about standing-waves
for the rest of the lives.

Just change the name to TLI (Transmitter Loading Indicator) which is
what it is and does very well. The true meaning and associations of
SWR will then emerge and all will be flooded with the light of reason.
----
Reg, G4FGQ.

SWR again.
 

Owen Duffy wrote:
Have it your way Cecil...

I hope you now see the advantage of being able to vary the
length of the ladder-line until a current maximum point is
located at the choke-balun. Knowing the impedance is purely
resistive and relatively low allows me to read it with my
MFJ-259B. That resistive point is on the ladder-line SWR circle
on the Smith Chart. An arc of the SWR circle is the known length
of the feedline which gives me the feedpoint impedance of the
antenna (and can be adjusted for losses).
--
73, Cecil http://www.qsl.net/w5dxp

SWR again.
 

Reg Edwards wrote:
You then include in the calculation the measurement or assumption of
the Zo of the 50-ohm coax, and the measurement or assumption of Zo of
the twin-line, and the forward and reverse powers, and the SWR on the
twin line can be deduced or assumed.

Actually, nowadays I use my MFJ-259B to read the resistance at
the choke-balun where I have adjusted the ladder-line length to
guarantee the existence of a current maximum point. It's actually
easier to do than to write about it. An assumption that Z0=50 ohms
is not necessary.

But if you think you are measuring SWR on anything you are cheating
and fooling yourself.

I actually have an SWR meter calibrated for balanced 380 ohms but it's
in a box somewhere in my garage. I found my indirect measurements to
be entirely accurate enough. In general, if one can isolate the problem
to 10% of the Smith Chart, one can solve any problem by tweaking.

Speaking of indirect measurements - let's say the feedline Z0 is 380
ohms with a VF of 0.9 and a length of 90 ft. The measured resistance
at the current maximum point is 30 ohms on 7.15 MHz. The SWR on the
ladder-line is 380/30 = 12.7:1. The feedline is 0.727 wavelengths
long. Plot the point 30/380 = 0.079 + j0 on a Smith Chart. Draw an
SWR circle through that point. Backtrack from that point around the
circle for 0.727 wavelengths and there's your antenna feedpoint
impedance (neglecting losses). Losses can be taken into account by
using SWR spirals instead of SWR circles. And of course, all of this
is done by a computer program after just a few seconds of data entry.
--
73, Cecil http://www.qsl.net/w5dxp

SWR again.
 

Reg Edwards wrote:
Line input Z = R+jX and to aggravate matters the meter discards all
information about X.

All the more reason to feed the line at a current maximum point
where X is known to be zero.
--
73, Cecil http://www.qsl.net/w5dxp

SWR again.
 

Reg Edwards wrote:

Cecil, I note you have changed the name from "SWR Meter" to "Forward &
Reverse Power Meter", a procedure I have been recommending for years.
Congratulations!

I think that was probably used to describe the Bird which,
to the best of my knowledge, has no SWR scale on the meter
face.

Now my Autek WM-1 actually has an "SWR meter" on the front
panel in addition to the "watt meter". I don't use a tuner
and it computes the actual SWR on the RG-213 going to my G5RV.
I achieve an SWR very close to 1:1 on the RG-213 on all HF bands
by varying the length of the balanced series section. 36 feet
of ladder-line works for 40m and 17m, my two favorite bands.
--
73, Cecil http://www.qsl.net/w5dxp

SWR again.
 

Saandy , 4Z5KS wrote:
What we did was one of two things: either tune the system for maximum
current in the line or else used a light bulb in conjunction with a
small light bulb and tuned for maximum brilliance. in neither case was
SWR involved in the mess.

It was around 1949 when I started hanging out at W5OLV's
shack. He had a homebrew 1625 transmitter with a parallel
tank circuit. The plug-in tank coil had a few turns of wire
wrapped around the bottom and that was the transmitter output.
He didn't use a tuner. He had a pickup loop that he slid up
and down the line until he located a current maximum point.
He cut the line at that point and fed it directly from the
transmitter. He added or subtracted turns on the plug-in coil
until he was satisfied. I didn't really understand what he was
doing until I studied the Smith Chart in college almost ten years
later. I now use that same basic technique with my 50 ohm
SGC-500 amplifier.
--
73, Cecil http://www.qsl.net/w5dxp

SWR again.
 

"Reg Edwards" wrote in message
...

"Jerry Martes" wrote
I have no understanding of why you find it important to state things
that
are not true about VSWR.

===================================
Jerry,

It is important because the SWR meter is EDUCATIONAL. It is more than
a pair of red and green LED's on our automatic tuners.

All along I have stated that the name of the so-called SWR meter
should be changed. Other more technical statements have been made to
convince they whose state of mind prevents agreement.

Remarkably few people disagree with my technical statements but offer
no reasons for disagreement or prove me to be incorrect.

SWR meters are by far the most prevelent topic on amateur radio
newsgroups. It appears time and time again in contexts which
demonstrate it to be a source of misunderstandings, arguments and
general confusion.

I maintain that the instrument's name is the root cause of the
problems. It does not do what its name says it does. This inevitably
leads people, not just novices and CB-ers, into incorrect channels of
thought which become deeply ingrained. It unnecessarily introduces
SWR into discussions which actually have nothing to do with SWR. And
worst of all, when operating equipment, it causes people to have
problems which either don't exist or are different to what people
imagine they are. Mis-education is the keyword.

Re-naming should begin in amateur radio handbooks and similar
publications. Editors should be the first to be educated.

SWR meters are seldom mentioned as such in professional text books.
They are given other more correct names. Terman manages very well
wthout them. But there's nothing wrong with his bibles. (Yes, I know
they probably hadn't been invented in his day.)

Perhaps when our Chinese friends enter the amateur radio market,
manufacturers' wisdom will allow the light of reason to shine through.
But they will have to get a move on. I can foresee the time when
automatic tuners are universal and the only meter on black boxes will
be the S-meter.

I don't doubt that you thoroughly understand how the so-called SWR
meter works. But even the present discussion is enough to demonstrate
that a simple change is needed. In the end it all reduces to
economics and survival of the fittest argument.
----
Reg, G4FGQ


Naw Reg, I dont have the slightest idea how a "VSWR meter" works. I was
too quick with my response about the worth of VSWR. I thought the
discussion was aimed toward the VSWR itself.
I've got to re-read that story about Silence is Golden and put it to
practice.

Jerry

SWR again.
 

On Tue, 29 Nov 2005 14:14:15 GMT, Cecil Moore wrote:

Owen Duffy wrote:
Have it your way Cecil...

I hope you now see the advantage of being able to vary the
length of the ladder-line until a current maximum point is
located at the choke-balun. Knowing the impedance is purely
resistive and relatively low allows me to read it with my
MFJ-259B. That resistive point is on the ladder-line SWR circle
on the Smith Chart. An arc of the SWR circle is the known length
of the feedline which gives me the feedpoint impedance of the
antenna (and can be adjusted for losses).

Cecil, you have a single solution, and you are inclined to transform
every problem to require that single solution (read your posts).

Whilst step variable length transmission lines have application, they
are not the solution to every problem, or indeed, to many problems.
You are not the originator, nor the only user of such.

Since you mention the Smith chart, you are a champion of operating
transmission lines at very high VSWR, and yet would suggest that a
Smith chart can give you an adequate solution for the losses. That
says more of what you consider adequate than the suitability of the
Smith chart as a solver of that type of problem, especially in this
day and age. I suggest that the Smith chart loss solution is adequate
when you can ignore the losses.

I can visualise you sitting amidst an expensive heap of inch size
pieces of LDF5-50 and a Bird 43, slide rule and Smith chart, with a
caption "It is possible, and it is practical!".

Yes, you could say that I understand the advantages of a step variable
length transmission line. It is probably why they are used as much as
they are.

Owen
--

SWR again.
 

On Tue, 29 Nov 2005 15:02:15 GMT, Cecil Moore wrote:

Reg Edwards wrote:
You then include in the calculation the measurement or assumption of
the Zo of the 50-ohm coax, and the measurement or assumption of Zo of
the twin-line, and the forward and reverse powers, and the SWR on the
twin line can be deduced or assumed.

Actually, nowadays I use my MFJ-259B to read the resistance at
the choke-balun where I have adjusted the ladder-line length to
guarantee the existence of a current maximum point. It's actually
easier to do than to write about it. An assumption that Z0=50 ohms
is not necessary.

But if you think you are measuring SWR on anything you are cheating
and fooling yourself.

I actually have an SWR meter calibrated for balanced 380 ohms but it's
in a box somewhere in my garage. I found my indirect measurements to
be entirely accurate enough. In general, if one can isolate the problem
to 10% of the Smith Chart, one can solve any problem by tweaking.

Speaking of indirect measurements - let's say the feedline Z0 is 380
ohms with a VF of 0.9 and a length of 90 ft. The measured resistance
at the current maximum point is 30 ohms on 7.15 MHz. The SWR on the
ladder-line is 380/30 = 12.7:1. The feedline is 0.727 wavelengths
long. Plot the point 30/380 = 0.079 + j0 on a Smith Chart. Draw an
SWR circle through that point. Backtrack from that point around the
circle for 0.727 wavelengths and there's your antenna feedpoint
impedance (neglecting losses). Losses can be taken into account by
using SWR spirals instead of SWR circles. And of course, all of this
is done by a computer program after just a few seconds of data entry.

So what is the answer to your example, the load Z, with and without
consideration of the losses?
--