Propagation velocity through coax's with different velocity factors?

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Discussion Overview

The discussion revolves around the effects of different velocity factors in transmission lines on wave propagation and reflections within a series circuit. It explores theoretical implications and analogies related to transmission line behavior.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant questions how differing velocity factors in transmission lines with the same characteristic impedance (Zo) affect wave velocity and whether this leads to reflections.
  • Another participant asserts that reflections occur only with changes in line impedance, not merely due to changes in velocity factor.
  • A different participant claims that changes in velocity factor do not result in bunching of waves, as wavelength also changes.
  • One participant provides an analogy comparing wave propagation to traffic flow, suggesting that while speed may change, the time period and vehicle count remain constant, implying that line length is not a critical factor.

Areas of Agreement / Disagreement

Participants express differing views on the relationship between velocity factor changes and reflections, with no consensus reached on the implications of these changes for wave behavior in transmission lines.

Contextual Notes

Participants have not fully resolved the implications of velocity factor changes on wave propagation and reflections, and assumptions regarding the relationship between impedance and velocity factor remain unexamined.

hobbs125
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Hi everyone,

I have been studying transmission lines and it got me thinking.

If we have a series circuit which has two equal length transmission lines with the same Zo but with different velocity factors how does this effect the wave velocity through the circuit?

Do the waves travel faster through one line and then slow down and bunch up in the other?

Does the mismatch in velocity factor produce reflections even through the Zo and length of each line is identical?
 
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The reflections on a line are due to changes in line impedance.
There is no reflection at a change in velocity factor unless there is also a change in impedance.
 
When velocity factor changes, wavelength changes so there is no bunching.
 
The constant here is the period, frequency or pulse repetition rate.

There is a good analogy with traffic on a road that has an increase in speed limit.
The vehicles are further apart, but they still have the same time period between vehicles and the same number of vehicles per hour.

The length of the road or transmission line is not important.
 

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