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?
--

SWR again.
 

Owen Duffy wrote:
So what is the answer to your example, the load Z, with and without
consideration of the losses?

Sorry, I just got a new Dell and don't have my software loaded.
A quick pencil whipping of a Smith Chart graph yields a
load around 1140 - j1900 ohms which would be about right
for a 145 ft. dipole on 40m.
--
73, Cecil http://www.qsl.net/w5dxp

SWR again.
 

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

No, my solution allows me to pull Reg's leg in arguments about
SWR meters since I don't use a tuner. :-) My solution also allows
me to get by without a 500 watt tuner for my SGC-500. The other
advantages are just frosting on the cake.
--
73, Cecil http://www.qsl.net/w5dxp

SWR again.
 

On Tue, 29 Nov 2005 21:35:33 GMT, Cecil Moore wrote:

Owen Duffy wrote:
So what is the answer to your example, the load Z, with and without
consideration of the losses?

Sorry, I just got a new Dell and don't have my software loaded.
A quick pencil whipping of a Smith Chart graph yields a
load around 1140 - j1900 ohms which would be about right
for a 145 ft. dipole on 40m.

You didn't differentiate between the lossy and lossless solutions. The
difference isn't very much, I figure about 1100-j2000 vs 1000-j2170
which is real hard to resolve on the Smith chart. Smith chart programs
solve the same tranmission line problems as underlies the Smith chart,
but using a program provides much higher resolution, and the
convenience and accuracy benefit of not having to find the solution in
a normalised domain.

The Smith chart does not directly indicate the mismatch loss in the
general case.

My online calculator at http://www.vk1od.net/tl/tllce.php produces an
answer (considering loss) of 422.87-j1441.91 if the transmission line
was 90' Wireman 552 and using Wes's characterisation of 552 for
derivation of the fundamental line parameters (slightly different Zo
to yours). Indicated line loss is 0.93 dB. (SWR is not used to arrive
at the solution.)

Dan's TLD gives 432.7-j1459.0 using a slightly different transmission
line approximation, and independently deriving the model from Wes's
characterisation. Indicated line loss is 0.93 dB.

This demonstrates the sensitivity of the result to very slight
variations in line parameters, consideration of loss, and the
approximations used in modelling.

Owen
--

SWR again.
 

"Owen Duffy" wrote in message
...
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?

Hi Owen

Did you mean to write the load impedance as 0.079 + j0? Or did you mean
0.079 + j1?

Jerry

SWR again.
 

Jerry Martes wrote:
Did you mean to write the load impedance as 0.079 + j0? Or did you mean
0.079 + j1?

0.079 + j0 is the normalized impedance at a current
maximum point at the transmitter. The load impedance
is not given.
--
73, Cecil http://www.qsl.net/w5dxp

SWR again.
 

"Cecil Moore" wrote in message
. net...
Jerry Martes wrote:
Did you mean to write the load impedance as 0.079 + j0? Or did you
mean 0.079 + j1?

0.079 + j0 is the normalized impedance at a current
maximum point at the transmitter. The load impedance
is not given.
--
73, Cecil http://www.qsl.net/w5dxp

I have *no* excuse for my not being able to read and think. i did
re-read the post and see whats being done.

Jerry

SWR again.
 

On Tue, 29 Nov 2005 22:30:16 GMT, "Jerry Martes"
wrote:


Did you mean to write the load impedance as 0.079 + j0? Or did you mean
0.079 + j1?

I didn't write that, it was Cecil, and j0 would be correct.

Owen
--

SWR again.
 

"Reg Edwards" wrote in news:dmf4fr$4cu$1
@nwrdmz01.dmz.ncs.ea.ibs-infra.bt.com:


"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)

Heh heh. I remember one time a friend of mine was wailing that his fancy
new outdoor 2m antenna wasn't working as good as the indoor mag-mount on
a pie plate that he had been using.

I asked about his installation and he informed me that the antenna was
properly installed and that the SWR was 1 to 1. So I inquired further.
He was using a bridge to measure reflected power at the transmitter. And
there really wasn't any. Then I asked him what he was using for
transmission line. Turns out it was about 75 feet of cheap RG58. So I
told him to take it off the antenna and see what the bridge said with no
antenna. It climbed all the way to 1.2 to 1. In short, the coax was
simply eating the power. Changing it out to better quality line proved
to be the answer there.

SWR is so overrated. I'm in the process of putting together a modest
balcony-based HF station. I'm much more interested in the efficiency of
loading coils than in actual SWR on the coax. A 3-to-1 SWR on coax is
meaningless at 80 meters. It adds only a fraction of a decibel to
losses, even in RG58. But your transmitter might not like the complex
load it is seeing at the end of that coax, hence the utility of a tuning
device. Back in the day, I used to just ignore such issues because my
transmitters had pretty good output tuning networks. But with the advent
of broadbanded solid state finals, it is necessary to match the radio to
the transmission line's complex input impedance.

--
Dave Oldridge+
ICQ 1800667

SWR again.
 

"Saandy , wrote
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,

You are a man after my own heart.

I would further simplify it. No need to mention SWR. It is
meaningless. Just make sure the transmitter is loaded with about 50
ohms and leave it at that.

To make things nice and tidy, just change the name of the meter to TLI
= Transmitter Loading Indicator.
----
Reg, G4FGQ

SWR again.
 

Saandy , 4Z5KS wrote:
...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

Some of what you say is very true. Especially in the world of HAM
radio. How ever, this being an open forum, truth is of great
importance. Your thesis on the "whys" of the importance of vswr
measurements are incorrect in some areas.
Yes, importance grew with the advent of coaxial lines simply because of
the relatively small distances between inner and outer conductors. That
part is true.

However, until you've seen a 6" universal coaxial transmission line with
no insulators or inner conductor remaining over a 350" run, I guess you
can't really appreciate the need for monitoring and maintaining good
"system" vswr characteristics.

Now to the measuring of said vswr. It can be done. In the broadcast
world it's accomplished through the measurement of "Return Loss". By
measuring the system return loss at the line input (generator end) and
deducting twice the line attenuation, we get an indication of the load
return loss thesis value is easily converted to vswr.

Return Loss:
This is the dB value of absolute reflection coefficient.
It is rather curious concept of transmission engineering.
This loss value becomes 0 for 100% reflection and becomes infinite for
an ideal connection.

RL = 20log((VSWR+1) / (VSWR-1))


Voltage Standing Wave Ratio (VSWR):
This is the ratio of maximum voltage to minimum voltage
in standing wave pattern.
It varies from +1 to infinite.

VSWR = (1+(10^RL/20)) / ((10^RL/20)-1)

These are good and valid measurements which should be performed at
initial installation of the system and periodically verified throughout
the system life.

Return Loss/VSWR is only one of many measurements that should be
periodically done. DC measurements such as megger. LO-Ohms are also
very important.




--
Over The Hill
__________________________________________________ ___________________________

The question of whether computers can think is like the question of
whether submarines can swim.

***Edsgar Dijkstra***

SWR again.
 

Owen Duffy wrote:
You didn't differentiate between the lossy and lossless solutions. The
difference isn't very much, I figure about 1100-j2000 vs 1000-j2170
which is real hard to resolve on the Smith chart.

Owen, it's pretty obvious that you were manufactured with a
lower tolerance (+/- 0.1%) than I was (+/- 20%). :-) Over on
QRZ.com, I suggested that the average amateur radio operator
has a hard time implementing a choke in a high-impedance
environment. W8JI said he could do it. I responded that, by
no stretch of the imagination, was he an "average amateur
radio operator". :-)
--
73, Cecil http://www.qsl.net/w5dxp

SWR again.
 

On Wed, 30 Nov 2005 17:08:27 GMT, Cecil Moore wrote:


Owen, it's pretty obvious that you were manufactured with a
lower tolerance (+/- 0.1%) than I was (+/- 20%). :-) Over on

Perhaps...

Now, I think you have told us over several articles that you are using
an SGC500 into a 30 ohm load on 7.15MHz. That 30 ohm load is a result
of feeding a dipole with 90' of ladderline, which I estimate has 0.9dB
of loss under those circumstances.

If your transmitter was delivering 500W to the feedline, about 100W is
lost in the feeder.

Do you know how much power your amplifier delivers to the feedline? It
is likely that with a load VSWR of 1.7 it may have reduced output, it
is also possible that it is delivering even more than 500W to the low
Z load.

Owen
--

SWR again.
 

Owen Duffy wrote:
Now, I think you have told us over several articles that you are using
an SGC500 into a 30 ohm load on 7.15MHz.

Now please be a gentleman and please don't go putting words in my mouth.
Here a quote of my exact words:

"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."

Clearly, "let's say", is a hypothetical postulate. I freely admit that
I pulled those values out of thin air. Going back to my web page reveals
that the feedpoint impedance on 40m for my 130 ft. dipole was really 38
ohms. Nonetheless, I can still make my point assuming the 30 ohm value
which would have been perfectly acceptable to me.

If your transmitter was delivering 500W to the feedline, about 100W is
lost in the feeder.

With a 1.7:1 SWR???? Maybe you should reprogram your calculator to take
the square root???? The ratio of Pref/Pfor for an SWR of 1.7:1 is 0.067.
Methinks you might be using the voltage reflection coefficient?

500(0.067) is 34 watts, not 100 watts. The SGC-500 laughes at 34 watts
reflected. (I swear that is true. I have heard it laughing to itself in
the wee hours during a contest.) Seriously, that amp is not known as
"The Brick" just because it looks like a brick.

Do you know how much power your amplifier delivers to the feedline? It
is likely that with a load VSWR of 1.7 it may have reduced output, it
is also possible that it is delivering even more than 500W to the low
Z load.

An SWR of 1.7:1 is nothing to worry about unless you think the percentage
power reflected is the same as the percentage voltage reflected. Don't feel
bad, many others have made that same mistake. Most people are programmed not
to think within a power/energy context and it gets them into trouble with
such concepts as "reflected power just sloshes around from side-to-side" and
"gobbledegook" applied to any attempt to track energy in a transmision line.

The SGC-500 is speced to tolerate an SWR of 6:1. That means that it can
dissipate more than half of its output power and keep on ticking. I
don't recommend allowing that to happen but that spec is why I don't worry
at all about reflected power unless the SWR is in excess of 2:1.

If we keep arguing, one of us is bound to make a mistake that the other
catches. I would guess that your above mistake bothers you a lot more
than it bothers me. :-)
--
73, Cecil http://www.qsl.net/w5dxp

SWR again.
 

Cecil Moore wrote:

Owen Duffy wrote:
If your transmitter was delivering 500W to the feedline, about 100W is
lost in the feeder.

With a 1.7:1 SWR???? Maybe you should reprogram your calculator to take
the square root???? The ratio of Pref/Pfor for an SWR of 1.7:1 is 0.067.
Methinks you might be using the voltage reflection coefficient?

Sorry, I read that as 100W lost in the amplifier. Macular Degeneration
strikes again.
--
73, Cecil http://www.qsl.net/w5dxp

SWR again.
 

On Wed, 30 Nov 2005 21:35:32 GMT, Cecil Moore wrote:

Owen Duffy wrote:
Now, I think you have told us over several articles that you are using
an SGC500 into a 30 ohm load on 7.15MHz.

Now please be a gentleman and please don't go putting words in my mouth.

Well, there was some uncertainty, and it is why I opened with "I
think...".

Here a quote of my exact words:

"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."

Clearly, "let's say", is a hypothetical postulate. I freely admit that
I pulled those values out of thin air. Going back to my web page reveals
that the feedpoint impedance on 40m for my 130 ft. dipole was really 38
ohms. Nonetheless, I can still make my point assuming the 30 ohm value
which would have been perfectly acceptable to me.

If your transmitter was delivering 500W to the feedline, about 100W is
lost in the feeder.

With a 1.7:1 SWR???? Maybe you should reprogram your calculator to take
the square root???? The ratio of Pref/Pfor for an SWR of 1.7:1 is 0.067.
Methinks you might be using the voltage reflection coefficient?

Ok, I saw your later post where you have note that you were on the
wrong track here.


500(0.067) is 34 watts, not 100 watts. The SGC-500 laughes at 34 watts
reflected. (I swear that is true. I have heard it laughing to itself in
the wee hours during a contest.) Seriously, that amp is not known as
"The Brick" just because it looks like a brick.

Do you know how much power your amplifier delivers to the feedline? It
is likely that with a load VSWR of 1.7 it may have reduced output, it
is also possible that it is delivering even more than 500W to the low
Z load.

An SWR of 1.7:1 is nothing to worry about unless you think the percentage
power reflected is the same as the percentage voltage reflected. Don't feel
bad, many others have made that same mistake. Most people are programmed not
to think within a power/energy context and it gets them into trouble with
such concepts as "reflected power just sloshes around from side-to-side" and
"gobbledegook" applied to any attempt to track energy in a transmision line.

The SGC-500 is speced to tolerate an SWR of 6:1. That means that it can
dissipate more than half of its output power and keep on ticking. I
don't recommend allowing that to happen but that spec is why I don't worry
at all about reflected power unless the SWR is in excess of 2:1.

Lets leave that issue alone.


If we keep arguing, one of us is bound to make a mistake that the other
catches. I would guess that your above mistake bothers you a lot more
than it bothers me. :-)

Well, I think we are agreed that you made a mistake in identifying a
mistake, if I am not mistaken!

No, back on track, I thought you might have measured forward and
reflected power at the amplifier output on the 30 ohm load, to deduce
the net forward power, then by allowing for the line loss, you would
have the net power at the feedpoint (most of which will be radiated in
some direction or another).

One could then calculate the performance of the feed configuration
compared to what would be delivered to an ideal nominal load with no
feed loss.

The whole excercise goes nowhere, because it seems that the 30 ohms
scenario is "hypothetical".

Owen
--

SWR again.
 

Owen Duffy wrote:
Well, I think we are agreed that you made a mistake in identifying a
mistake, if I am not mistaken!

Your original mistake was in making a posting that caused me to
misunderstand. :-) Your loss calculator gives 0.762 dB loss for
90 feet of Wireman #445 with an SWR of 12.7:1 on 7.15 MHz.

The whole excercise goes nowhere, because it seems that the 30 ohms
scenario is "hypothetical".

I knew it was thirty-something ohms so I said "30". It was
actually 38 ohms indicating an SWR at the source of 1.3:1.
That's acceptable losses for me. If I used an antenna tuner
to achieve a 1:1 match, it would probably be a wash.

Which is probably a good question. At what SWR should one
install an antenna tuner? My IC-706 seems perfectly
happy at 2:1.
--
73, Cecil http://www.qsl.net/w5dxp

SWR again.
 

Reg Edwards wrote:

Gerry,

The load is the antenna - about which the SWR meter knows absolutely
nothing. All the the meter has to work with is the input impedance of
the tuner or the transmission line.

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



The load that counts is what the transmitter sees. Which is what his
instrument measures.

tom
K0TAR

SWR again.
 

On Wed, 30 Nov 2005 23:42:33 GMT, Cecil Moore wrote:

Owen Duffy wrote:
Well, I think we are agreed that you made a mistake in identifying a
mistake, if I am not mistaken!

Your original mistake was in making a posting that caused me to
misunderstand. :-) Your loss calculator gives 0.762 dB loss for
90 feet of Wireman #445 with an SWR of 12.7:1 on 7.15 MHz.

Now, you're trying to trick me... did you mean Wireman 554?

It does show 0.76dB for 90' of 554 with a 30+j0 input Z at 7.15MHz.

The 0.9dB stated earlier was (as stated) for 552 which had a Zo closer
to your 380 ohms, whereas 554 is 360 ohms.


The whole excercise goes nowhere, because it seems that the 30 ohms
scenario is "hypothetical".

I knew it was thirty-something ohms so I said "30". It was
actually 38 ohms indicating an SWR at the source of 1.3:1.
That's acceptable losses for me. If I used an antenna tuner
to achieve a 1:1 match, it would probably be a wash.

Which is probably a good question. At what SWR should one
install an antenna tuner? My IC-706 seems perfectly
happy at 2:1.

Given that some radios (including the IC706-IIG) reduce drive power at
high VSWR as a protection mechanism, you may want to install an ATU to
develop full power output. My recollection is that the power output of
the IC706-IIG is significantly down at VSWR=2, but it probably also
depends on the actual load impedance.

A likely scenario could be that the radio only develops 50W of output,
and only 40W makes it to the feedpoint (assuming 1dB feed loss). The
ATU might raise that to 100W of output, less tuner loss and feed loss
giving 75 to 80W at the feedpoint. Mere fraction of an S point... but
if you have a 100W transmitter, might as well use it, and besides, the
technical challenge of achieving that goal and measuring the
achievement might be part of what amateur radio is about.

Owen
--

SWR again.
 

The load that counts is what the transmitter sees. Which is what
his
instrument measures.

tom
K0TAR

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

I fully agree the transmitter load is what the transmitter sees.

But his meter does not measure it.

His meter simply tells him whether or not its resistance is 50 ohms.

Which is all he wants to know anyway.
----
Reg, G4FGQ

SWR again.
 

On Thu, 1 Dec 2005 06:46:58 +0000 (UTC), "Reg Edwards"
wrote:

But his meter does not measure it.

Jerry has a slotted line - described here in loving detail some time
ago. It and the meter so attached is perfectly capable of measuring
all the factors stated.

Which is all he wants to know anyway.

which is an assumption (or a forced argument, take your pick) as he
has already reconciled any mis-understandings.

SWR again.
 

"Richard Clark" wrote

Jerry has a slotted line - described here in loving detail some time
ago. It and the meter so attached is perfectly capable of measuring
all the factors stated.

Which is all he wants to know anyway.

which is an assumption (or a forced argument, take your pick) as he
has already reconciled any mis-understandings.
========================================

Richard, please explain what purpose is served by the above message.
Am I missing something?
---
Reg.

SWR again.
 

On Thu, 1 Dec 2005 07:52:23 +0000 (UTC), "Reg Edwards"
wrote:
Richard, please explain what purpose is served by the above message.

Again? En Française? Auf Deutsch?

Am I missing something?
On Sun, 27 Nov 2005 04:39:17 +0000 (UTC), "Reg Edwards" wrote:
If the discussion should drift towards my personal character...

You have nothing left to say? ...seems bloody unlikely. Anyway, we
will hear it again soon enough. Just like the soft drink advert:
Grab your BAWLS and run and run and run!

[ http://enx.org/img/bawlsarmy.jpg ]

SWR again.
 

Owen Duffy wrote:
Now, you're trying to trick me... did you mean Wireman 554?

Yep, no trick, just tricky fingers, getting worse with age.

The 0.9dB stated earlier was (as stated) for 552 which had a Zo closer
to your 380 ohms, whereas 554 is 360 ohms.

I measured the 554 at 380 ohms. I could have been off by 5%.

Given that some radios (including the IC706-IIG) reduce drive power at
high VSWR as a protection mechanism, you may want to install an ATU to
develop full power output. My recollection is that the power output of
the IC706-IIG is significantly down at VSWR=2, but it probably also
depends on the actual load impedance.

I have never witnessed my IC-706 folding back at any resistive
load between 25 ohms and 100 ohms. My IC-706 manual says, "When
the SWR is *higher* than approx. 2.0:1, the transceiver's power
drops to protect the final transistors."
--
73, Cecil http://www.qsl.net/w5dxp