Rotational speed
 

K7ITM wrote:
This has been educational. Clearly there are people in both camps.
I'm obviously in the non-rotating camp, and it seems to be one with a
high population.

I thought the non-rotating camp was the only one. Because
of that, I need to apologize to Roy, W7EL, who is apparently
in the rotating camp when he said that standing-wave phasors
have a rotational speed the same as the traveling wave. Since
he doesn't read my postings, would you please reply to this
one so he will see it? TNX
--
73, Cecil http://www.w5dxp.com

Rotational speed
 

K7ITM wrote:
More from my research (which is probably at an end at this point):

Bell, "Fundamentals of Electric Circuits," calls a phasor a rotating
vector, period.

IEEE Standard Dictionary of Electrical and Electronic Terms has
entries for both non-rotating and rotating definintions.

Christiansen, "Electronic Engineers' Handbook," defines a phasor
clearly as a non-rotating quantity.

This has been educational. Clearly there are people in both camps.
I'm obviously in the non-rotating camp, and it seems to be one with a
high population. I'll be careful to ask when someone writes of
phasors and their definition is not clear from the context, at least
if the distinction between the two definitions matters in that case.

I still haven't had the time to post the quotes. But I did look over Van
Valkenburg carefully, and he very clearly describes the quantity
including exp(jwt) as a phasor, and a page or two later describes the
term without the time-varying term as a phasor. So he uses both
definitions -- but I can't find anywhere that he actually defines
exactly what a phasor is. I got that text because it's one of the most
widely used circuits texts. Pearson and Maler, I have left over from
college -- I took classes from both of them, and we know how that works.

I'm happy to call a phasor a rotating vector or, better yet, a
description of a rotating vector (the description consisting of phase
and amplitude). This way, I can have my rotation without needing to have
the phasor itself rotate. The important thing, as I see it, is to
realize that:

-- It results from a substitution of a complex time-varying quantity for
a real time-varying quantity;
-- The time-varying part of the complex quantity is not used in
calculations because it cancels; and
-- The fact that the complex quantity is time-varying is essential to
the method and solution.

but I guess it's up to the individual to decide whether he wants to
declare that time-varying part (exp(jwt)) to be part of the "phasor" or
something just attached to it.

Thanks, this has been stimulating and educational. I'll still try to get
those quotes down.

Roy Lewallen, W7EL

Rotational speed
 

Roy Lewallen wrote:
but I guess it's up to the individual to decide whether he wants to
declare that time-varying part (exp(jwt)) to be part of the "phasor" or
something just attached to it.

Here's a quote from "Optics", by Hecht:
"Because both phasors rotate together at a rate w,
we can simply freeze them at t=0 and not worry
about their time dependence, which makes them a
lot easier to draw."

This is what EZNEC does - freeze the feedpoint
current at t=0 to 1 amp at zero degrees. The
current reported by EZNEC at loads is then
referenced to that feedpoint current phasor.

The fact remains that the phase of the total
current in a standing wave antenna, like a 1/2WL
dipole or a loaded mobile antenna, cannot be used
to measure the phase shift in a wire, much less
be used to measure the phase shift in a loading
coil.
--
73, Cecil http://www.w5dxp.com

MFJ-259
 

MFJ-259
Dropped from the roof LCD display broken (all black}. Dos any one know
what the description of the lcd is, or manufacturer P/n ? I like to by
from a supplier not MFJ there replacement parts are very expensive .
ie. meter $60 found one on line $3.00 MFJ #50-247-3
TNX JB K1JZP

Rotational speed
 

Cecil, W5DXP wrote:
"Here`s a quote from "Optics" by Hecht:
"Because bith phasors rotate together at a rate w, we can simply freeze
them at t=0 and not worry about their time dependence, which makes them
a lot easier to draw."

Raymond B. Yarbrough writes in the 5th ed. of "Electrical Engineering
Reference Manual" on page 1-1:
"A complex number can also be represented as a two-dimensional vector
in a complex plane. Thus, the complex number can be written in polar or
phasor form as

a+jb=c on an angle phi

c=square root of a squared + b squared

phi = arctan (b/a) "

On page 3-15 Yarborugh wrote:
In electric circuits involving sinusoids it is more convenient to deal
with RMS values of voltage and current rather than with peak values, and
with angles in degrees rather than with radians (Angles in the
exponential form must be in radians for mathematical calculations.)

Thus, an alternative representation, which is called the effective value
phasor notation has evolved."

Best regards, Richard Harrison, KB5WZI

Rotational speed
 

Charles M. Close in "The Analysis of Linear Circuits" has this
footnote in a section called Representing Sinusoidal Function of Time:

"Although directed lines are commonly called vectors, this terminology
is avoided in this application. In field theory, quantities that have
an orientation in three-dimensional space and that are sinusoidal
functions of time are encountered. The term "vector" then refers to
the spacial orientation, and the term "rotating phasor" to the
exponential terms [Fe^jwt and its complex conjugate]. Since both
phasors and vectors are complex quantities, phasors are added and
subtracted in the same way as vectors."

According to the text, since the two complex functions of t in
exponential form can be graphically represented as directed lines, and
since each is the conjugate of the other, they are called
counter-rotating phasors. They each make w/2pi revolutions per second
and have an angular frequency of w radians per second.

ac6xg


Richard Harrison wrote:
Cecil, W5DXP wrote:
"Here`s a quote from "Optics" by Hecht:
"Because bith phasors rotate together at a rate w, we can simply freeze
them at t=0 and not worry about their time dependence, which makes them
a lot easier to draw."

Raymond B. Yarbrough writes in the 5th ed. of "Electrical Engineering
Reference Manual" on page 1-1:
"A complex number can also be represented as a two-dimensional vector
in a complex plane. Thus, the complex number can be written in polar or
phasor form as

a+jb=c on an angle phi

c=square root of a squared + b squared

phi = arctan (b/a) "

On page 3-15 Yarborugh wrote:
In electric circuits involving sinusoids it is more convenient to deal
with RMS values of voltage and current rather than with peak values, and
with angles in degrees rather than with radians (Angles in the
exponential form must be in radians for mathematical calculations.)

Thus, an alternative representation, which is called the effective value
phasor notation has evolved."

Best regards, Richard Harrison, KB5WZI

Rotational speed
 

Jim Kelley wrote:
According to the text, since the two complex functions of t in
exponential form can be graphically represented as directed lines, and
since each is the conjugate of the other, they are called
counter-rotating phasors.

Is it talking about forward and reflected currents?
If the forward and reflected currents are of equal
magnitudes, which direction does the standing-wave
current phasor rotate?
--
73, Cecil http://www.w5dxp.com

MFJ-259
 

JB MacDonald wrote:

MFJ-259
Dropped from the roof LCD display broken (all black}. Dos any one know
what the description of the lcd is, or manufacturer P/n ? I like to by
from a supplier not MFJ there replacement parts are very expensive .
ie. meter $60 found one on line $3.00 MFJ #50-247-3
TNX JB K1JZP
many years ago I broke the display on my 259. I located the display
supplier but they would not sell me one. They claimed they had a
exclusive contract with MFJ. I sent the unit in and MFJ repaired the
display. I don't remember what it cost then.
Check with MFJ as to repair costs.

Dave WD9BDZ

Rotational speed
 

Cecil Moore wrote:
Jim Kelley wrote:

According to the text, since the two complex functions of t in
exponential form can be graphically represented as directed lines, and
since each is the conjugate of the other, they are called
counter-rotating phasors.


Is it talking about forward and reflected currents?

It's talking about electromagnetic wave functions, so it applies to
actual electromagnetic waves.

If the forward and reflected currents are of equal
magnitudes, which direction does the standing-wave
current phasor rotate?

A clue might have been in one of the parts you deleted said that
phasors add just like vectors. A standing 'wave' is not as much a
wave as it is an interference pattern. It is an amplitude as a
function of position, not as a function of time. The phasor for a
standing wave would then rotate as a function of position; the
direction of rotation would depend on the direction you're moving
along the transmission line.

73, Jim AC6XG

Rotational speed
 

Jim Kelley wrote:
The phasor for a standing wave would then
rotate as a function of position; the direction of rotation would depend
on the direction you're moving along the transmission line.

What if I'm not moving - just sitting still at a point?
--
73, Cecil http://www.w5dxp.com