"Bob Myers" wrote in news:MmdPh.1809
:


"Dave Oldridge" wrote in message
9...
If the lossless transmission line (obviously no such animal exists)
were
tuned with a lossless tuner, then VSWR would not matter at all.

Dave, I'm pretty sure I know what you mean here, but it should
be noted that this isn't entirely true. The line would have to have a
couple
of other characteristics besides being simply "lossless" for VSWR
not to matter at all.

Not if there's a lossless tuner.

The problem, of course, is that a VSWR of other than 1:1 implies
(by definition!) that the voltages and currents along the length of
the line are not constant; there are cyclic variations in each, with
maxima and minima located at half-wavelength intervals (that's
the whole "standing wave" thing in the first place, right?).
Particularly in high-power situations, it is possible for the maxima
to exceed the ratings of the source or of the line itself.

In which case it's not truly "lossless" (and after breakdown becomes VERY
lossy).



--
Dave Oldridge+
ICQ 1800667

billcalley wrote:
What I gleaned from the excellent answers for the original "VSWR
Doesn't Matter?" thread is that high VSWR doesn't really matter in a
lossless transmission line environment between a transmitter's antenna
tuner and the antenna, since any reflected RF energy will simply
continue to "bounce" back and forth between the tuner's output
impedance and the antenna's input impedance until it is, finally,
completely radiated from the antenna without loss.

But then why does the concept of "mismatch loss" exist in
reference to antennas? I have quickly calculated that if a
transmitter outputs 100 watts, and the TX antenna has an impedance
that will cause a VSWR of 10:1 -- using lossless transmission line --
that the mismatch loss in this "lossless" system would be 4.81dB!
(Reflected power 66.9 watts, RL -1.74).

Since mismatch loss is the "amount of power lost due to
reflection", and is as if an "attenuator with a value of the mismatch
loss where placed in series with the transmission line", then I would
think that VSWR would *definitely* matter, and not just for highly
lossy lines either. But here again, I'm probably not seeing the
entire picture here. What am I missing??

Confused!

-Bill


I think the confusion (which *always* seems to arise)
comes from the mix of the concept with the real world.
The concept claims that the system is lossless, so the
power bounces around until it eventually exits the "system"
via the antenna. Real world, the system is lossy, so
with all the bouncing around some of the power fails to
leave the system via RF radiation and instead leaves
the system via IR radiation. More heat, less RF.
Tastes great, less filling. :-)

Ed

On Thu, 29 Mar 2007 13:10:46 -0700, billcalley wrote:

What I gleaned from the excellent answers for the original "VSWR
Doesn't Matter?" thread is that high VSWR doesn't really matter in a
lossless transmission line environment between a transmitter's antenna
tuner and the antenna, since any reflected RF energy will simply
continue to "bounce" back and forth between the tuner's output
impedance and the antenna's input impedance until it is, finally,
completely radiated from the antenna without loss.

But then why does the concept of "mismatch loss" exist in
reference to antennas? I have quickly calculated that if a
transmitter outputs 100 watts, and the TX antenna has an impedance
that will cause a VSWR of 10:1 -- using lossless transmission line --
that the mismatch loss in this "lossless" system would be 4.81dB!
(Reflected power 66.9 watts, RL -1.74).

Since mismatch loss is the "amount of power lost due to
reflection", and is as if an "attenuator with a value of the mismatch
loss where placed in series with the transmission line", then I would
think that VSWR would *definitely* matter, and not just for highly
lossy lines either. But here again, I'm probably not seeing the
entire picture here. What am I missing??

Confused!


It truly wouldn't matter if there were no such thing as resistance
and so on. The whole circuit could be tuned, with the transmission line
a part of it, and all of the power would go out the antenna.

Unfortunately, that's not the way reality works, more's the pity.

Every time those "standing waves" bounce back and forth, they warm
up the transmission line, the connectors, the transmitter tank, the
transmitter itself, etc, etc, and Entropy is conserved. ;-)

Hope This Helps!
Rich

On Mar 29, 8:15 pm, Rich Grise wrote:
Every time those "standing waves" bounce back and forth, they warm
up the transmission line, the connectors, the transmitter tank, the
transmitter itself, etc, etc, and Entropy is conserved. ;-)


Humor noted, but Entropy is not conserved.

Entropy increases

bw wrote:
Entropy increases

Seems to me that evolution violates that principle.
--
73, Cecil http://www.w5dxp.com

"Cecil Moore" wrote in message
. net...
bw wrote:
Entropy increases

Seems to me that evolution violates that principle.
--
73, Cecil http://www.w5dxp.com

Not to mention the Noble Prize Ilya Prigogine won for "Dissipative
Structures" in 1977.

Spontaneous Ordered Structures arising out of disorder. But it takes an
Energy Flow to produce them.

Robert

"Robert" wrote in message
link.net...

"Cecil Moore" wrote in message
. net...
bw wrote:
Entropy increases

Seems to me that evolution violates that principle.
--
73, Cecil http://www.w5dxp.com

Not to mention the Noble Prize Ilya Prigogine won for "Dissipative
Structures" in 1977.

Spontaneous Ordered Structures arising out of disorder. But it takes an
Energy Flow to produce them.

Robert

Sorry. Forgot to include the link.

http://en.wikipedia.org/wiki/Ilya_Prigogine

Robert

"Cecil Moore" wrote in message
. net...
bw wrote:
Entropy increases

Seems to me that evolution violates that principle.

Not at all; "entropy increases" is with respect to the total
entropy of a closed system. But in the case of "evolution,"
the only closed system which makes any sense to consider
is the entire solar system, or at the very least the Sun-Earth
system. It is entirely pemissible for an overall increase in entropy
to occur (i.e., the Sun slowly loses energy to the rest of the
universe) while at the same time this overall trend results in
a very localized DECREASE in entropy (increase in order;
in this case, the evolution of complex systems on Earth).

Bob M.

--
73, Cecil http://www.w5dxp.com

Bob Myers wrote:
"Cecil Moore" wrote in message
... while at the same time this overall trend results in
a very localized DECREASE in entropy (increase in order;
in this case, the evolution of complex systems on Earth).

How about considering the localized W5DXP system? :-)
--
73, Cecil http://www.w5dxp.com

Cecil Moore wrote:
bw wrote:

Entropy increases


Seems to me that evolution violates that principle.


Duh, life always violates it locally, but makes the sum total of entropy
higer than it would have been. You aren't the idiot you appear, I hope.

tom
K0TAR