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Michael A. Terrell wrote:
Rich Grise wrote:
Michael A. Terrell wrote:
What do you think? A loaded AM broadcast tower uses the ground for
the counterpoise. A dipole antenna is two radiators fed 180 degrees
out of phase.
THEY ARE NOT "OUT OF PHASE"!!!!!!!!!!
They are perfectly _IN_ phase, but of opposite polarity.
With a sinusoid, the result of a polarity reversal _LOOKS_ exactly the
same as a 180 degree phase shift, but they are _FAR_ from the same thing.
To test this, just try it with a pulse:
_ _ _ _
__| |____| |____| |____| |___ <-- start here
__ ____ ____ ____ ___
|_| |_| |_| |_| <-- polarity inversion
_ _ _ _
| |____| |____| |____| |___ <-- 180 degree phase shift
_NOW_ do you get it?
You don't use square waves for AM broadcast.
You must be a liberal. Change the subject rather than admit that you're in
error.
In article <ichn3q$c90$1@news.eternal-september.org>, Tim Williams wrote:
"Rich Grise" <richg@example.net.invalid> wrote in message
news:ichamg$4at$2@news.eternal-september.org...
THEY ARE NOT "OUT OF PHASE"!!!!!!!!!!
Uh, yes they are.
They are perfectly _IN_ phase, but of opposite polarity.
...Which is exactly 180 degrees phase.
With a sinusoid, the result of a polarity reversal _LOOKS_ exactly the
same as a 180 degree phase shift, but they are _FAR_ from the same
thing.
To test this, just try it with a pulse:
_ _ _ _
__| |____| |____| |____| |___ <-- start here
__ ____ ____ ____ ___
|_| |_| |_| |_| <-- polarity inversion
If you had gone to school, you'd have performed Fourier transforms and
been taught that:
F{-f(t)} = -F{f(t)} = F{f(t)} * e^pi
i.e., negation of the time-domain function is negation = multiplied by
e^pi = 180 degree phase shift of the frequency-domain function.
Would you like a proof? It becomes obvious from the integral.
What is NOT obvious is any other phase shift besides 0 and 180. Here's an
example of a "brick wall" filtered square wave (up to, I think, the 15th
harmonic), with an equal phase shift applied to all harmonics, in 10
degree increments.
http://webpages.charter.net/dawill/Square_Phaseshift.gif
It's clearly flat-topped inbetween, if still quite squiggly due to Gibbs'
phenomenon. It looks more triangular at 90 degrees, except for the strong
peak.
The halfway point (i.e., 90 / 270 degrees) is known as the Hilbert
transform. Naturally, no finite network exists which has this behavior
(flat response, 90 degree phase shift); it's usually approximated with a
truncated series of all-pass filters, or computed in DSP.
You are saying that shifting each harmonic by 180 degrees of its
individual frequency is the same as inverting polarity of the whole as
well as all individual harmonics. That is true.
Rich was saying shifting a waveform by 180 degrees of its fundamental
frequency is not the same as inversion - which is true when there is "lack
of halfwave symmetry"
(negative half cycle is not an inverted repeat of positive half cycle).
(True when even harmonics are present, false when even harmonics are
absent).
That's what I'm saying - they might _look_ identical, but they got there byRich was saying shifting a waveform by 180 degrees of its fundamental
frequency is not the same as inversion - which is true when there is "lack
of halfwave symmetry"
(negative half cycle is not an inverted repeat of positive half cycle).
(True when even harmonics are present, false when even harmonics are
absent).
So how do _you_ know so well which one it is, if they look the same?Michael A. Terrell wrote:
What do you think? A loaded AM broadcast tower uses the ground for
the counterpoise. A dipole antenna is two radiators fed 180 degrees out
of phase.
THEY ARE NOT "OUT OF PHASE"!!!!!!!!!!
They are perfectly _IN_ phase, but of opposite polarity.
With a sinusoid, the result of a polarity reversal _LOOKS_ exactly the
same as a 180 degree phase shift,
By where it comes from. A phase shift has some reactive element thatOn 11/23/2010 10:10 PM, Rich Grise wrote:
Michael A. Terrell wrote:
What do you think? A loaded AM broadcast tower uses the ground for
the counterpoise. A dipole antenna is two radiators fed 180 degrees out
of phase.
THEY ARE NOT "OUT OF PHASE"!!!!!!!!!!
They are perfectly _IN_ phase, but of opposite polarity.
With a sinusoid, the result of a polarity reversal _LOOKS_ exactly the
same as a 180 degree phase shift,
So how do _you_ know so well which one it is, if they look the same?
(CT Transformer, inverting amp) it's simply a polarity inversion.I would tend to agree with you if a wideband balun is used to generate
the pair of signals. But if someone chooses to do it with a 1/2
wavelenght delay it's better described as "out of phase".
If it's done with a phase shifter, then yes, it's phase shifted. Otherwise,