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Unformatted text preview: (please be gentle with the bayonet connectors) – what happens to the reflection pulse now? Explain why
this change occurred in the hand-in sheet. B. Speed of the signal in the cable
Measure the round-trip time of a signal pulse through a wire and back by noting the time interval between
the original and reflected pulse.
1. Remove the terminator so that the reflection pulse is again prominent. You will now measure the time
interval between the original and reflection pulses. Press the Cursor button near the middle of the dozen
buttons at the top of the face of the scope – this will now change the on-screen Menu on the right of the
scope screen. The Menu selections can be made by pressing on the buttons immediately to the right of the
screen; press the button to the right of Type (twice) so that the Time cursors are activated – you should now
see two vertical lines on the screen.
2. The currently-controlled cursor should be highlighted in white on the right of the screen; select Cursor 1,
then turn the Multipurpose knob (leftmost knob, with green LED) to adjust its position so that it lines up
with the first peak. Then switch to Cursor 2 and line it up with the reflection peak. The time difference t can be read and recorded immediately. From this, and from the length of the cable, you should be
able to find out the speed of the signal in the cable. Express this in units of c (speed of light) and record in
hand-in sheet. (Hint: for a reflection to occur, what direction(s) does a pulse need to travel in the cable?) C. Speed of light in air
Measure how long it takes for the pulse to leave the laser and arrive at the diode detector.
1. First, turn off half of the classroom ceiling lights. It may be much easier to align the laser beam with
the detector if some of the room lights are off.
2. Plug in the detector to CH1 using the other shorter coaxial cable. Make sure the T-connector on that
channel is properly terminated.
3. You will have to shoot the laser be...
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This document was uploaded on 12/27/2012.
- Summer '09