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Funny little problem - can you answer?
FriedMule:
I have just seen a video and decided to ask you to solve this little interesting question.
You have some RG58 coaxial cable and your trusted DMM ohm-meter.
What would your meter show if you measured 1 yard of the cable, end to end?
Now let's make the cable be insanely long, let's say from earth, around the moon and back again, an about 2 light-second journey.
What will your Ohm-meter show if you measured the cable? Remember that your DMM can measure several times before the signal has traveled for the 2 seconds necessary to go all the way. :-)
Ian.M:
'RG58' is more of a general description of the cable's approximate physical size and nominal impedance than an electrical spec. Reputable brand RG58 cables can have center conductor DC resistances from under 10 to over 35 milliohms/meter and an even wider range for shield resistance. However most DMMs are lousy at measuring low (milliohm) resistance values so odds are unless your DMM supports Kelvin (4 wire) resistance measurements, a yard of coax will read pretty much the same as shorting the test leads
If you could connect a multimeter to the ends of a cable that extends in a loop out to lunar orbit, the most likely result is destruction of the multimeter due to induced currents in the cable!
rs20:
Are you connecting to the centre conductors or the shields at each end? Presuming the centre conductors, are the shields floating or grounded at the ends, or grounded regularly? Are the shields at the two ends connected?
Assuming the shields are connected at the ends, and we're measuring between the conductors, I'd expect 100 ohms for the first second (assuming a 2 light-second loop), then a bunch of reflection nonsense, eventually settling on 10-35 millohms/meter * c * 2 s (stealing Ian.M's numbers).
free_electron:
your question is underdefined. where are the probes connected ?
coax cable has 4 terminals
A : left side center conductor
B : left side shield
C : right side center conductor
D : right side shield
where are the probes ?
what with the unused terminal ? float ? short ?
Benta:
That the meter will measure several times before the signal returns is irrelevant.
You'll have some settling time on your result, but normally the current source for resistance measurement is constantly on (=DC), unless it's a special pulse measurement.
Stop watching idiotic YT videos.
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