02-10-2016, 07:07 PM
(02-10-2016, 06:03 PM)pwdrive Wrote: How would one measure the inductance of that screened cable?
Without the ability to put both ends of an already installed cable in the same place (to measure L with an LCR meter), you could determine L by first measuring the characteristic impedance of the line. That involves a pulse generator, an oscilloscope, and a variable resistor in the 200 ohms region. That's an experiment that's worth doing for fun anyway.
Having established Z, and knowing C, then L can be determined by rearranging Z=√(L/C). I've done that in the past, and it gives pretty reasonable results.
Assuming it's a 50 ohm cable, the inductance might well be 4.4uH, give or take. At 20kHz, the reactance of 4.4uH is insignificant. As is - in fairness - 1.77nF, which gives a -3dB point of 150kHz when fed from 600 ohms. Real sources should have much lower Zout than that, but some might not. Such as Terry's microphone
So, this cable of Trevor's is clearly fine for the purpose. Certainly, he's unlikely to be bothered by reflections, etc, given how short it is, and having looked at the numbers, HF loss is not a serious issue either. But yes, of the two, capacitance is usually the most significant at audio, so yes, it's a good "figure of merit" here.
