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From: zen cycle <funkmasterxx@hotmail.com>
Newsgroups: rec.bicycles.tech
Subject: Re: Fine Tuning Shifting
Date: Wed, 14 Aug 2024 19:22:06 -0400
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> On 8/14/2024 3:35 PM, cyclintom wrote:
>> 
>>
>> Flunky just talks ahbout crap that he doesn't know about. Notice how 
>> he could not answer how you measure the length of a wire 
>> electronically? That's because he personally doesn't know how to use 
>> an oscilloscope. Which comes as no

Or, It could be because Jeff answered it as well as I could so I didn't 
feel it was worth commenting, but since you insist, here's how you test 
cable length with _out_ using dedicated TDR equipment:

- Connect a pulse generator, an oscilloscope, and the cable under test 
together with a T connector (Typically BNC, but adaptors may be required 
depending on the equipment.
- set up a pulse generator to single pulse, starting with a 1 nS width, 
5 V P-P.
- Set up the scope to trigger on the single pulse from the generator, 
with the pulse from the generator being displayed at the extreme left of 
the display.
- Adjust the time base of the oscilloscope until the reflected pulse 
appears on the right side of the display while manually initiating the 
pulse on the generator.*
- Longer cable lengths may make the returned pulse not quite 
discernible. When the trigger pulse is no longer visible, increase the 
pulse width until it is visible, then begin adjusting the time base 
again until the reflected pules is visible (It may also be necessary to 
increase the pulse amplitude).
- Once the reflected pulse is visible, measure the distance between the 
trigger pulse and the reflected pulse on the scope as time delay (Hence 
the term Time Domain Reflectometry).
- PLug this delay into the propagation delay value for the cable under 
test, and do the math.

* setting up the generator to a repetitive pulse could prove problematic 
in that the trigger pulse period my be shorter than the propagation 
delay of the cable under test giving a confusing display. A competent 
technician could manage it, but given the bizarre and completely 
non-nonsensical method you described, it's well beyond your comprehension.