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cable lenght meter

Posted: Tue Jan 08, 2019 8:23 am
by muratcoskun
Hi everyone

İ need a cable lenght meter but i dont have any idea about how can i do it ?

it need to measure the length of the non-powered cable and display the coordinates and cable length online. ( it will worked by GSM)
it will be able to do the measurement at regular intervals or when I want.

i want to see online For example:

Cable Number :2 Lenght: 445,3m coordinate : 49.015577, 5.710104 Time : 03:22 PM

is there someone who can help me ?

Re: cable lenght meter

Posted: Tue Jan 08, 2019 10:25 pm
by ElectroNick
Just brainstorming:

Getting a serial gps unit and connecting it to the RP is the easy part.
now for the hard part: assuming you have access only to one cable end;
I would get also a Low freq RF directional coupler. connect it properly to the cable, RF in and RF out;
sweep the frequency range and plotting what is the return signal. I would start from this idea. Basically I would use the cable as an antenna, since I do not know what frequency it has, I sweep the hole range and I see where It resonates. The issue I'm afraid is like for instance, 445m would translate to a resonance of 0.00224719101 Hz, witch is weird. No.
I think a better idea is to send a pulse and wait for the echo. Like this user here:
do a gogole or youtube search for "#37: Use a scope to measure the length and impedance of coax"
He used the oscilloscope and pulse generator.
Good luck! - and please let us know your progress