Coaxial cable, resistor and oscilloscope

[sunrise_]

I'm studying the trasmission of signals though coaxial cable; I'm using a coaxial cable (of course!), an oscilloscope, a generator an some different endings. This is the scheme: https://i.stack.imgur.com/OTGtq.jpg

I was told that if I use a very long cable that has impedence \$Z_0= 50 \Omega\$ and put, at the end of it, a **resistor of \$47\Omega \$**, the signal will be reflected.

I have obtained this: https://i.stack.imgur.com/EWvVD.jpg



If I have correctly understood, the height of the step pointed by the green arrow is the half of the V given by the generator.

I can't understand why the step pointed by the red arrow is shorter than the one that is on the other side. And I can't understand what's the physical meaning of the step pointed by the red arrow.
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Then, I have terminated the cable with a **short circuit** and I have obtained this: https://i.stack.imgur.com/5gohS.jpg


Could you explain me what's up at the points indicated by the two arrows and the yellow and red points?
________________

Then, I have terminated the cable with a **resistor of 100 ohm** and I have obtained this: https://i.stack.imgur.com/hbkkw.jpg

Could you explain me, why the step pointed by the green arrow is higher than the step pointed by the red arrow?

 

[FvM]

For a serious discussion, please provide some informations:
- generator pulse width
- generator output impedance (probably 50 ohm)
- length of each cable segment
- oscilloscope time base
- which oscilloscope trace refers to which signal
- oscilloscope input impedance (I presume high impedance)

At first sight, the waveforms don't match the setup shown in the diagram. The first waveform would fit an unterminated (RL >> 50 ohm) case.

 

[sunrise_]

For a serious discussion, please provide some informations:
- generator pulse width
- generator output impedance (probably 50 ohm)
- length of each cable segment
- oscilloscope time base
- which oscilloscope trace refers to which signal
- oscilloscope input impedance (I presume high impedance)

At first sight, the waveforms don't match the setup shown in the diagram. The first waveform would fit an unterminated (RL >> 50 ohm) case.

You're right.. I'm sorry. I don't know the exact data..
-oscilloscope input impedance: high impedance
-Ch1 is the lower trace, Ch2 is the upper trace, please see the diagram in the first link
-length of each cable segment: in this experience, only one cable was used and its lenght was very very long

That's all I know!

 

[FvM]

The waveforms are showing this values of termination impedance ("terminazione") Z2 and respective reflection factor r
1. Z2 = ∞, r = +1
2. Z2 = 0 , r = -1
3. Z2 = 100, r = +1/3

The real waveforms show a small additional attenuation of the reflected wave, mainly due to oscilloscope input impedance and cable loss.