Re: [EVGRAY] J ² = 1

Body

Hi Ole,

> On 22 Nov 2018, at 18:51, [email protected] [EVGRAY] <[email protected]> wrote:
> 
> Both ways can be used. For low inductance of a current shunt let the return wire go close to and in parallel with the shunt resistor to minimize any area for the magnetic field.
> 
> Here the return wire is twisted around the current shunt.
> 
> Also the 50 Ohm feed through is necessary. Without it a lot of reflections will happen unless the scope itself has a 50 Ohm input. As scope inputs usually are 1M Ohm the signal will be reflected due to the great impedance mismatch from 50m Ohm to 1M Ohm and the signal will drown in noise. 50m Ohm to 50 Ohm reduces the reflections a lot.

Thanks for the pic (illustrates it well). I already have such a 50 Ohm feed through but never really understood what exactly it does and therefore have never used it. I understand it has an impedance of 50 Ohm like the coax cable to prevent reflexions, yes, but how does it transfer the potential difference to be measured (over the shunt) to the 1M Ohm impedance input of the scope. If we had to build such a 50 Ohm feed through what would we have to do (what is it composed of)? This might help me to understand how it works. 

Thanks a lot,

 Andreas