Cecil, W5DXP wrote:
"There is nothing at the mouth of the stub capable of causing
reflections. All the reflections occur at the shorted end of the stub."

Correct, if the generator matches Zo. In any case, Zo limits current on
the transmission line until a reflection from the mismatched load
arrives back at the line input to change the impedance seen by the
generator. Then, the current delivered by the generator will depend on
the generator`s match to the new impedance caused by the reflection
after a few iterations.

Another view of the mismatched line is to ignore what the transmitter
can deliver into any load. Then, the forward and reflected waves simply
cause a current in each direction depending on the strength and the
current allowed by Zo.

Transmission lines are tyrannical in forcing current in a particular
direction to adhere to the Zo voltage to current ratio. That`s the
reason a junction between lines of differing impedances produce a
reflection. The line from the source contains a voltage wave and a
current wave conforming to Zo. The line of a different impedance
connected to the line from the source accepts alll the voltage or
current available to it which leaves a surplus of either voltage or
current that must be reflected back toward its source. The source line
is no less dictatorial about its Zo to the reflection than it is to the
incident wave.

Best regards, Richard Harrison, KB5WZI

Microwave waveguide is just an infinite number of 1/4 wave stubs connected
mount to mouth.

--
73
Hank WD5JFR
"Richard Harrison" wrote in message
...
Cecil, W5DXP wrote:
"There is nothing at the mouth of the stub capable of causing
reflections. All the reflections occur at the shorted end of the stub."

Correct, if the generator matches Zo. In any case, Zo limits current on
the transmission line until a reflection from the mismatched load
arrives back at the line input to change the impedance seen by the
generator. Then, the current delivered by the generator will depend on
the generator`s match to the new impedance caused by the reflection
after a few iterations.

Another view of the mismatched line is to ignore what the transmitter
can deliver into any load. Then, the forward and reflected waves simply
cause a current in each direction depending on the strength and the
current allowed by Zo.

Transmission lines are tyrannical in forcing current in a particular
direction to adhere to the Zo voltage to current ratio. That`s the
reason a junction between lines of differing impedances produce a
reflection. The line from the source contains a voltage wave and a
current wave conforming to Zo. The line of a different impedance
connected to the line from the source accepts alll the voltage or
current available to it which leaves a surplus of either voltage or
current that must be reflected back toward its source. The source line
is no less dictatorial about its Zo to the reflection than it is to the
incident wave.

Best regards, Richard Harrison, KB5WZI

On Thu, 17 Jun 2004 16:34:55 GMT, "Henry Kolesnik"
wrote:
Microwave waveguide is just an infinite number of 1/4 wave stubs connected
mount to mouth.

Hi Hank,

Actually, that would make a sealed cavity. Perhaps you meant cheek to
jowl?

73's
Richard Clark, KB7QHC

How is that possible, considering that a rectangular waveguide operates
well in single mode over about a 1.5 to 1 frequency range, and has a
different field distribution than a transmission line (TE01 vs TEM)?

Roy Lewallen, W7EL

Henry Kolesnik wrote:

Microwave waveguide is just an infinite number of 1/4 wave stubs connected
mount to mouth.

On Thu, 17 Jun 2004 16:34:55 GMT, "Henry Kolesnik"
wrote:
Microwave waveguide is just an infinite number of 1/4 wave stubs connected
mount to mouth.

Hi Hank,

Actually, that would make a sealed cavity. Perhaps you meant cheek to
jowl?

73's
Richard Clark, KB7QHC


I thought that was "cheek by jowl."
73,
Tom Donaly, KA6RUH

Henry, WD5JFR wrote:
"Microwave waveguide is just an infinite number of 1/4 wave stubs
connected mouth to mouth."

It`s true that a waveguide is the same as any number of shorted 1/4-wave
shorted stubs connected in parallel. Their parallel connection between
the same two points will not affect their resonant frequency. That`s
why, as Richard Clark noted, if the 1/4-wave shorted stubs are circled
around into the form of a closed container, it makes a resonant cavity.
The diameter of the drum formed by the large number of 1/4-wave stubs
has a diameter of 1/2-wavelength at the resonant frequency.

Rectangular waveguide is more or less aperoiodic down to the low
frequency limit of its propagation. This occurs where its larger
cross-section dimension is 1/2-wavelength. Attenuation rises as
frequency through the waveghuide is lowered towards its cut-off at the
1/2-wavelength dimension. Below cut-off, attenuation is very high.

In the waveguide`s passband it is preferred to coax because
air-insulated coax has about 3X the loss of waveguide. But, waveguides
must be at least 1/2-wavelength wide which limits practical use to
microwaves. A waveguide for 30 MHz would be at least 17 feet wide.

Best regards, Richard Harrison, KB5WZI

On 17 Jun 2004 19:48:56 GMT, (Tdonaly) wrote:
On Thu, 17 Jun 2004 16:34:55 GMT, "Henry Kolesnik"
wrote:
Microwave waveguide is just an infinite number of 1/4 wave stubs connected
mount to mouth.

Hi Hank,

Actually, that would make a sealed cavity. Perhaps you meant cheek to
jowl?

73's
Richard Clark, KB7QHC

I thought that was "cheek by jowl."

You are right.

73's
Richard Clark, KB7QHC

Richard Clark wrote:

"Henry Kolesnik" wrote:
Microwave waveguide is just an infinite number of 1/4 wave stubs connected
mount to mouth.

Actually, that would make a sealed cavity.

He didn't say they were "shorted" stubs.



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