There has been some discussion in the past months about conjugate matching,
VSWR, and power transfer from source to load.
I've come across a puzzle while noodling on this.
My main issue here is how the heck my VSWR meter is measuring the way it is.

My elementary hook-up is an RF power amp feeding directly into a VSWR meter,
and from there into a load consisting of a carbon resistor and a variable
capacitor rigged in series. The meter connects to the load via about a foot of
50 ohm coax. The frequency is between 1 and 10 MHz.
Model the source impedance as Zs = R + jX, and the load impedance as Zl = r +
jx (or use phasors if you prefer .
The following two statements are true:
1) The power dissipated in the load (r) is maximised when x = -X (so-called
"conjugate matching"), whatever the value of (r).
2) The classical VSWR is minimised (zero "reflected power") when x = +X,
whatever the value of (r).

However, my VSWR meter, whch is a conventional 2-diode bridge and short
transmission line, indicates that minimum indicated VSWR
corresponds to max power dissipated in (r).!! (i.e. at conjugate match, and
NOT when reflected power is zero).

The equation normally used for VSWR is
VSWR = ABS( (1 + |p|) / (1 - |p|) )
where
p = (Zl - Zs) / (Zl + Zs)
and p is a measure of the amount of power reflected back to the source, called
the "voltage reflection coefficient"

I plotted something I call "conjugate VSWR" or VSWR*. which is the same
expression as above, but with p defined as
p = (Zl - Zs*) / (Zl + Zs)
where Zs* indicates the complex conjugate of Zs.
and the behaviour of this VSWR* thingie absolutely matches what I see on my
meter. Aye, there's the rub.

Some points to note
a) Classical VSWR shows NO minimum for all r, when x has the opposite sign to
X
b) VSWR* always has a minimum at the same r-value which causes maximum power
to be dissipated in r, whatever the value of x.

Again, I flat don't understand how my VSWR meter can indicate VSWR* when I
know it should indicate VSWR.

Here are a couple of links to flesh out the theory.

1. Wade through this at your peril - it's you lot fighting abou this issue and
is VERY long
http://www.ibiblio.org/pub/academic/...S/20030831.ant

2. This is much more succint - cut to the chase on p47
http://my.ece.ucsb.edu/yorklab/Usefu...%20AN64-1B.pdf

Best,
Andrew

ok, bonzo, i'll bite on the troll bait. but only because its early in the
morning and the normal endless discussion of this stuff hasn't taken over
yet.

"Lord Snooty" wrote in message
nk.net...
There has been some discussion in the past months about conjugate
matching,
VSWR, and power transfer from source to load.
I've come across a puzzle while noodling on this.
My main issue here is how the heck my VSWR meter is measuring the way it
is.

My elementary hook-up is an RF power amp feeding directly into a VSWR
meter,
and from there into a load consisting of a carbon resistor and a variable
capacitor rigged in series. The meter connects to the load via about a
foot of
50 ohm coax. The frequency is between 1 and 10 MHz.
Model the source impedance as Zs = R + jX, and the load impedance as Zl =
r +
jx (or use phasors if you prefer .
The following two statements are true:
1) The power dissipated in the load (r) is maximised when x = -X
(so-called
"conjugate matching"), whatever the value of (r).

wrong. you must transform the R+jX along the transmission line to get back
to the load seen by the source. you stipulate a low frequency and short
line, so you are close anyway.

2) The classical VSWR is minimised (zero "reflected power") when x = +X,
whatever the value of (r).

doubly wrong. vswr is on a cable and is independent of the source. it
knows nothing of R+jX only the characteristic impedance of the cable. all
following calculations are wrong for this reason alone.


However, my VSWR meter, whch is a conventional 2-diode bridge and short
transmission line, indicates that minimum indicated VSWR
corresponds to max power dissipated in (r).!! (i.e. at conjugate match,
and
NOT when reflected power is zero).

The equation normally used for VSWR is
VSWR = ABS( (1 + |p|) / (1 - |p|) )
where
p = (Zl - Zs) / (Zl + Zs)

wrong again, the impedance used must be that of the cable not of the source.
its not worth commenting further until you understand this.

and p is a measure of the amount of power reflected back to the source,
called
the "voltage reflection coefficient"

I plotted something I call "conjugate VSWR" or VSWR*. which is the same
expression as above, but with p defined as
p = (Zl - Zs*) / (Zl + Zs)
where Zs* indicates the complex conjugate of Zs.
and the behaviour of this VSWR* thingie absolutely matches what I see on
my
meter. Aye, there's the rub.

Some points to note
a) Classical VSWR shows NO minimum for all r, when x has the opposite sign
to
X
b) VSWR* always has a minimum at the same r-value which causes maximum
power
to be dissipated in r, whatever the value of x.

Again, I flat don't understand how my VSWR meter can indicate VSWR* when I
know it should indicate VSWR.

Here are a couple of links to flesh out the theory.

1. Wade through this at your peril - it's you lot fighting abou this issue
and
is VERY long

http://www.ibiblio.org/pub/academic/...S/20030831.ant

2. This is much more succint - cut to the chase on p47

http://my.ece.ucsb.edu/yorklab/Usefu...%20AN64-1B.pdf

Best,
Andrew

From the previous posting, I can guess who is going to jump all over this.
Keep up the good work.

Tam
"Dave" wrote in message
...
ok, bonzo, i'll bite on the troll bait. but only because its early in the
morning and the normal endless discussion of this stuff hasn't taken over
yet.

"Lord Snooty" wrote in message
nk.net...
There has been some discussion in the past months about conjugate
matching,
VSWR, and power transfer from source to load.
I've come across a puzzle while noodling on this.
My main issue here is how the heck my VSWR meter is measuring the way it
is.

My elementary hook-up is an RF power amp feeding directly into a VSWR
meter,
and from there into a load consisting of a carbon resistor and a
variable
capacitor rigged in series. The meter connects to the load via about a
foot of
50 ohm coax. The frequency is between 1 and 10 MHz.
Model the source impedance as Zs = R + jX, and the load impedance as Zl
=
r +
jx (or use phasors if you prefer .
The following two statements are true:
1) The power dissipated in the load (r) is maximised when x = -X
(so-called
"conjugate matching"), whatever the value of (r).

wrong. you must transform the R+jX along the transmission line to get
back
to the load seen by the source. you stipulate a low frequency and short
line, so you are close anyway.

2) The classical VSWR is minimised (zero "reflected power") when x = +X,
whatever the value of (r).

doubly wrong. vswr is on a cable and is independent of the source. it
knows nothing of R+jX only the characteristic impedance of the cable. all
following calculations are wrong for this reason alone.


However, my VSWR meter, whch is a conventional 2-diode bridge and short
transmission line, indicates that minimum indicated VSWR
corresponds to max power dissipated in (r).!! (i.e. at conjugate match,
and
NOT when reflected power is zero).

The equation normally used for VSWR is
VSWR = ABS( (1 + |p|) / (1 - |p|) )
where
p = (Zl - Zs) / (Zl + Zs)

wrong again, the impedance used must be that of the cable not of the
source.
its not worth commenting further until you understand this.

and p is a measure of the amount of power reflected back to the source,
called
the "voltage reflection coefficient"

I plotted something I call "conjugate VSWR" or VSWR*. which is the same
expression as above, but with p defined as
p = (Zl - Zs*) / (Zl + Zs)
where Zs* indicates the complex conjugate of Zs.
and the behaviour of this VSWR* thingie absolutely matches what I see on
my
meter. Aye, there's the rub.

Some points to note
a) Classical VSWR shows NO minimum for all r, when x has the opposite
sign
to
X
b) VSWR* always has a minimum at the same r-value which causes maximum
power
to be dissipated in r, whatever the value of x.

Again, I flat don't understand how my VSWR meter can indicate VSWR* when
I
know it should indicate VSWR.

Here are a couple of links to flesh out the theory.

1. Wade through this at your peril - it's you lot fighting abou this
issue
and
is VERY long


http://www.ibiblio.org/pub/academic/...S/20030831.ant

2. This is much more succint - cut to the chase on p47


http://my.ece.ucsb.edu/yorklab/Usefu...%20AN64-1B.pdf

Best,
Andrew

nope, all done. reg is here and cecil can't be far behind. i've had my
fun, time to do other more productive things than watch them re-hash
conjugal matches for the next month or two.

"Tam/WB2TT" wrote in message
...
From the previous posting, I can guess who is going to jump all over this.
Keep up the good work.

Tam
"Dave" wrote in message
...
ok, bonzo, i'll bite on the troll bait. but only because its early in
the
morning and the normal endless discussion of this stuff hasn't taken
over
yet.

"Lord Snooty" wrote in message
nk.net...
There has been some discussion in the past months about conjugate
matching,
VSWR, and power transfer from source to load.
I've come across a puzzle while noodling on this.
My main issue here is how the heck my VSWR meter is measuring the way
it
is.

My elementary hook-up is an RF power amp feeding directly into a VSWR
meter,
and from there into a load consisting of a carbon resistor and a
variable
capacitor rigged in series. The meter connects to the load via about a
foot of
50 ohm coax. The frequency is between 1 and 10 MHz.
Model the source impedance as Zs = R + jX, and the load impedance as
Zl
=
r +
jx (or use phasors if you prefer .
The following two statements are true:
1) The power dissipated in the load (r) is maximised when x = -X
(so-called
"conjugate matching"), whatever the value of (r).

wrong. you must transform the R+jX along the transmission line to get
back
to the load seen by the source. you stipulate a low frequency and short
line, so you are close anyway.

2) The classical VSWR is minimised (zero "reflected power") when x =
+X,
whatever the value of (r).

doubly wrong. vswr is on a cable and is independent of the source. it
knows nothing of R+jX only the characteristic impedance of the cable.
all
following calculations are wrong for this reason alone.


However, my VSWR meter, whch is a conventional 2-diode bridge and
short
transmission line, indicates that minimum indicated VSWR
corresponds to max power dissipated in (r).!! (i.e. at conjugate
match,
and
NOT when reflected power is zero).

The equation normally used for VSWR is
VSWR = ABS( (1 + |p|) / (1 - |p|) )
where
p = (Zl - Zs) / (Zl + Zs)

wrong again, the impedance used must be that of the cable not of the
source.
its not worth commenting further until you understand this.

and p is a measure of the amount of power reflected back to the
source,
called
the "voltage reflection coefficient"

I plotted something I call "conjugate VSWR" or VSWR*. which is the
same
expression as above, but with p defined as
p = (Zl - Zs*) / (Zl + Zs)
where Zs* indicates the complex conjugate of Zs.
and the behaviour of this VSWR* thingie absolutely matches what I see
on
my
meter. Aye, there's the rub.

Some points to note
a) Classical VSWR shows NO minimum for all r, when x has the opposite
sign
to
X
b) VSWR* always has a minimum at the same r-value which causes maximum
power
to be dissipated in r, whatever the value of x.

Again, I flat don't understand how my VSWR meter can indicate VSWR*
when
I
know it should indicate VSWR.

Here are a couple of links to flesh out the theory.

1. Wade through this at your peril - it's you lot fighting abou this
issue
and
is VERY long



http://www.ibiblio.org/pub/academic/...S/20030831.ant

2. This is much more succint - cut to the chase on p47



http://my.ece.ucsb.edu/yorklab/Usefu...%20AN64-1B.pdf

Best,
Andrew

Dave wrote:
nope, all done. reg is here and cecil can't be far behind. i've had my
fun, time to do other more productive things than watch them re-hash
conjugal matches for the next month or two.

I guess I need to say this again. My take on discussions of conjugate
matching in ham antenna systems is that it is a waste of time. If reflected
energy is not allowed to reach the source, e.g. typical ham Z0-matched
systems, the source impedance is irrelevant and doesn't affect anything
in the system except for efficiency.
--
73, Cecil http://www.qsl.net/w5dxp



-----= Posted via Newsfeeds.Com, Uncensored Usenet News =-----
http://www.newsfeeds.com - The #1 Newsgroup Service in the World!
-----== Over 100,000 Newsgroups - 19 Different Servers! =-----

Sorry everyone, but I just retested with no cable and the results I obtain are
precisely the same. The coax cable was only 26" long anyway.
So forget about that transmission line stuff. It's irrelevant here. What I
want to know is why the VSWR indications are the way they are.

If anyone's interested, I can email a small spreadsheet that deals with this
simple circuit (V0-R-jX-r-jx) and allows you to set
a) R,X and r, and vary x
b) R,X and x, and vary r.
I plot side by side on the two corresponding graphs
- modulus of total load voltage
- modulus of load resistor voltage
- modulus of load reactance voltage
- power dissipated in load resistor
- VSWR between source and load
- "conjugate VSWR" between source and load.

One more time with feeling -
What I want to know is why the VSWR indications are the way they are.

Best,
Andrew

"Cecil Moore" wrote in message
...
Dave wrote:
nope, all done. reg is here and cecil can't be far behind. i've had my
fun, time to do other more productive things than watch them re-hash
conjugal matches for the next month or two.

I guess I need to say this again. My take on discussions of conjugate
matching in ham antenna systems is that it is a waste of time. If reflected
energy is not allowed to reach the source, e.g. typical ham Z0-matched
systems, the source impedance is irrelevant and doesn't affect anything
in the system except for efficiency.
--
73, Cecil http://www.qsl.net/w5dxp



-----= Posted via Newsfeeds.Com, Uncensored Usenet News =-----
http://www.newsfeeds.com - The #1 Newsgroup Service in the World!
-----== Over 100,000 Newsgroups - 19 Different Servers! =-----

Comment imbedded:

"Dave" wrote in message
...
ok, bonzo, i'll bite on the troll bait. ...

"Lord Snooty" wrote in message
nk.net...
...RF power amp feeding directly into a VSWR meter,
...into a load consisting of a carbon resistor and a variable
capacitor rigged in series. The meter connects to the load via about a
foot of 50 ohm coax. The frequency is between 1 and 10 MHz.
Model the source impedance as Zs = R + jX, and the load impedance as Zl
=
r +
jx (or use phasors if you prefer .
The following two statements are true:
1) The power dissipated in the load (r) is maximised when x = -X
(so-called
"conjugate matching"), whatever the value of (r).

wrong. you must transform the R+jX along the transmission line to get
back
to the load seen by the source. you stipulate a low frequency and short
line, so you are close anyway.

The "transform along the coax" part is correct, but the "power is
maximised" part can be VERY misleading folks.

P.S. Get this MPT theorm blockage out of your minds... It is a synthetic
restriction.
The "maximum power therom" (ZL=Zs) ONLY applies to ONE special case, NOT
all cases. That case is where the source's output power (or if you like
current) capability is limited ONLY by the two resistances. That is, the
case is when the source can put out all the power needed by these resistors
and no other internal limit dominates. A common circuit can be shown to
give maximum power at other than Zs=ZL (aparently violating the above
referred-to therom). There are things other than these resistances that
limit the output power of a
practical source.... (see how long this thread goes.....



2) The classical VSWR is minimised (zero "reflected power") when x = +X,
whatever the value of (r).

doubly wrong. vswr is on a cable and is independent of the source.

Without plodding through the rest, it appears Dave has a handle on the
error.



--
Steve N, K,9;d, c. i My email has no u's.

it
knows nothing of R+jX only the characteristic impedance of the cable. all
following calculations are wrong for this reason alone.


However, my VSWR meter, whch is a conventional 2-diode bridge and short
transmission line, indicates that minimum indicated VSWR
corresponds to max power dissipated in (r).!! (i.e. at conjugate match,
and
NOT when reflected power is zero).

The equation normally used for VSWR is
VSWR = ABS( (1 + |p|) / (1 - |p|) )
where
p = (Zl - Zs) / (Zl + Zs)

wrong again, the impedance used must be that of the cable not of the
source.
its not worth commenting further until you understand this.

and p is a measure of the amount of power reflected back to the source,
called
the "voltage reflection coefficient"

I plotted something I call "conjugate VSWR" or VSWR*. which is the same
expression as above, but with p defined as
p = (Zl - Zs*) / (Zl + Zs)
where Zs* indicates the complex conjugate of Zs.
and the behaviour of this VSWR* thingie absolutely matches what I see on
my
meter. Aye, there's the rub.

Some points to note
a) Classical VSWR shows NO minimum for all r, when x has the opposite
sign
to
X
b) VSWR* always has a minimum at the same r-value which causes maximum
power
to be dissipated in r, whatever the value of x.

Again, I flat don't understand how my VSWR meter can indicate VSWR* when
I
know it should indicate VSWR.

Here are a couple of links to flesh out the theory.

1. Wade through this at your peril - it's you lot fighting abou this
issue
and
is VERY long


http://www.ibiblio.org/pub/academic/...S/20030831.ant

2. This is much more succint - cut to the chase on p47


http://my.ece.ucsb.edu/yorklab/Usefu...%20AN64-1B.pdf

Best,
Andrew

Andrew,

Conjugate matching may be a very interesting subject and is indeed a much
discussed topic on these walls.

However, amongst the amateur fraternity, a "conjugate match" should be
classified as being off topic. It does not exist. Not even when the tuner
has been adjusted exactly for a VSWR equal to 1 to 1.

Why?

Because the internal impedance of the transmitter is not 50 ohms. It is not
relevant.

What is the internal impedance of YOUR transmitter? You will not find it
mentioned in the manufacturer's operating or maintenance handbooks. In all
likelihood you will not know what it is even if you designed and built the
transmitter yourself!
---
Reg, G4FGQ

On Sun, 23 May 2004 14:17:51 +0000 (UTC), "Reg Edwards"
wrote:

Because the internal impedance of the transmitter is not 50 ohms. It is not
relevant.

Old Son,

Lord Kelvinator would be saddened by such a dismissal of actually
delving into "knowing" by your meagre understanding that fails to
offer an actual value that it IS. Such superstition that dominates
this paucity would lead us to believe the Z is as slight as an angel
wafting past in a dream (would that be in English Units, or metric?).

Definitions by negatives is an amusing troll however. I do enjoy
participation in kind:

Let's see, the Z of a transmitter is NOT
a dead parrot, nor
five farthings, nor
10 inches, nor
a polka dot dress, nor
the gross national income of Lithuania, nor
the combined weight of all your dead white scientists.

I'm sure I missed a few.... ;-)

73's
Richard Clark, KB7QHC