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  #91   Report Post  
Old July 18th 03, 05:11 PM
Richard Clark
 
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On Fri, 18 Jul 2003 08:20:54 +0100, "Ian White, G3SEK"
wrote:
The same people produce the same arguments...


Hi Ian,

Your statement is a self-fulfilling example.

What purpose does it serve to merely say t'ain't so in place of
commenting on data taken in the field?

There are equipment operators.

There are bench techs.

There are some of both.

And then there are cut-and-paste theoreticians.

73's
Richard Clark, KB7QHC

  #92   Report Post  
Old July 18th 03, 05:17 PM
Richard Clark
 
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On Fri, 18 Jul 2003 09:28:07 -0400, "Tarmo Tammaru"
wrote:


"Dilon Earl" wrote in message
...
On Thu, 17 Jul 2003 09:06:32 -0500, "William E. Sabin"
[email protected] wrote:
If I have a 100 watt transmitter and my wattmeter shows 3 watts
reflected. Is 3 watts actually being dissipated in the tank and final
PA?

That would depend on the output impedance of the transmitter. If it is 50
Ohms, all the reflected power would be absorbed by the transmitter. If it is
0 Ohms or its Norton equivalent, it is all reflected, and none is
dissipated.

Tam/WB2TT


Hi Tam,

This is painfully obvious. It is also painfully demonstrative. It
also appears to be painfully avoided in lieu of providing an actual
value (Punchinello seems to wholly ignore his own cries that lacking
numbers renders such whining as ignorance).

I've read for years that the common RF rig is NOT a 50Ohm source, and
absolutely none dare commit themselves to just what value it is (much
less offer their own measure). Being a physical reality, the rig must
present some real value, but vacuous theory seems to bar that
discussion.

73's
Richard Clark, KB7QHC
  #93   Report Post  
Old July 18th 03, 05:48 PM
W5DXP
 
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Dr. Slick wrote:
How do they measure a "surge impedance"?


For a transmission line, it is the same as the characteristic
impedance. For a traveling wave antenna, it is the same as
the feedpoint impedance. So for a center-fed standing wave
antenna, like a dipole, you could terminate the ends of the antenna
to eliminate reflections and then measure the feedpoint impedance.

Standing wave antennas are like transmission lines with standing
waves. The impedance at any point is the (forward voltage wave
plus the reflected voltage wave) divided by the (forward current
wave plus the reflected current wave). The feedpoint impedance
of traveling wave antennas is usually about 600-800 ohms according
to The ARRL Antenna Book.
--
73, Cecil, W5DXP

  #94   Report Post  
Old July 18th 03, 05:51 PM
W5DXP
 
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Dick Carroll wrote:
You can be just as sure that the speaker presents its rated impedance only
at one frequency, too.


Is it still 1000 Hz?
--
73, Cecil, W5DXP

  #95   Report Post  
Old July 18th 03, 05:57 PM
W5DXP
 
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Roy Lewallen wrote:
What needs to be thrown away is the belief that all impedances are the
ratio of a voltage to a current, along with the notion that only
resistors can have resistance.


I agree, Roy, but what can we do about it? I had been using "virtual
impedance" to differentiate a voltage to current ratio from an intrinsic
physical impedance. How would you differentiate an intrinsic physical
impedance from a voltage to current ratio?
--
73, Cecil, W5DXP



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Old July 18th 03, 07:29 PM
Roy Lewallen
 
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You can do about it what you like. What I've chosen to do about it is to
try and educate the people who will listen, and ignore those who won't.
I find the concepts perfectly understandable without the need for
additional adjectives.

Roy Lewallen, W7EL

W5DXP wrote:
Roy Lewallen wrote:

What needs to be thrown away is the belief that all impedances are the
ratio of a voltage to a current, along with the notion that only
resistors can have resistance.



I agree, Roy, but what can we do about it? I had been using "virtual
impedance" to differentiate a voltage to current ratio from an intrinsic
physical impedance. How would you differentiate an intrinsic physical
impedance from a voltage to current ratio?
--
73, Cecil, W5DXP


  #97   Report Post  
Old July 18th 03, 07:33 PM
Roy Lewallen
 
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And the mice are off.

Is it just my perception, or is it the fate of all threads in this
newsgroup to end up being Cecil arguing about power waves?

Cecil, have you considered starting your own newsgroup, say
alt.cecils.power.waves?

Roy Lewallen, W7EL

W5DXP wrote:
Ian White, G3SEK wrote:

"Where does the reflected power go?" is even worse because it contains
at least two built-in misconceptions: that reflected power waves
exist, and that they have to "go" somewhere.



Ian, it can be proven that reflected power waves exist. Ramo & Whinnery
say they exist. Standing waves in a single source, single feedline,
single load system cannot exist without reflected waves. The HP Application
Note AN 95-1 defines the power in reflected waves. "|a2|^2 = Power
reflected
from the load." Saying something is a misconception is only an opinion
that differs from a lot of expert opinions. . .


  #98   Report Post  
Old July 18th 03, 07:54 PM
Roy Lewallen
 
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How about light bulbs, solar panels, thermocouples, batteries, fuel
cells, and fireflies?

Roy Lewallen, W7EL

Tarmo Tammaru wrote:
Any transducer I can think of offhand converts between mechanical energy and
electrical energy, as for instance a loudspeaker, microphone, mechanical
filter, etc.

As for the impedance of free space, one way to build a stealth aircraft is
to cover it with material that has a resistivity of 377 Ohms/square. Then
there is no reflection

Tam/WB2TT



  #99   Report Post  
Old July 18th 03, 08:09 PM
Richard Clark
 
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On Fri, 18 Jul 2003 11:45:13 -0700, Roy Lewallen
wrote:

Sigh. I guess one more time. A mouse in the maze.


No cheese at the end of that one.

I'm firmly in agreement with Bill and Ian on this one.

Roy Lewallen, W7EL


your's and other opinions merely supports my contention:

I've read for years that the common RF rig is NOT a 50Ohm source, and
absolutely none dare commit themselves to just what value it is (much
less offer their own measure). Being a physical reality, the rig must
present some real value, but vacuous theory seems to bar that
discussion.

73's
Richard Clark, KB7QHC


I still find it strange that the savants and pundits will say what it
is NOT, but NOT what it IS.

Is one Ohm too much?

Is ten thousand Ohms too little?

Do anyone of you have a simple number that must exist as a physically
verifiable entity of a physical example commonly available to any Ham?

What is it that heats up in the presence of mismatch that all
manufacturers go to great length to protect against? Does it have to
be a carbon resistor to qualify? Which one? Why is it so hard to
quantify in the face of such firm agreement among you gentlemen? My
guess is that you would refuse to warrant your answer in the face of
catastrophic failure - evidence contrary to your opinions.

Sorry, but puzzles and enigmas do not answer the reality of heat and
heat does not arrive through the offices of some virtualized component
born of substituted theories of matching.

73's
Richard Clark, KB7QHC
  #100   Report Post  
Old July 18th 03, 08:19 PM
Jim Kelley
 
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W5DXP wrote:
Point is that "maximum possible power" will cause a lot of transmitters
to exceed their maximum power rating and overheat.


How much is the maximum possible power? H-Bomb? Gamma ray burst? Big
Bang? ;-)

73, ac6xg


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