Faraday cages and cables

Quite so - the idea of ground being some magical '0V' is not really true, certainly between points that are far apart in terms of the speeds of the signals in question - there simply is no time for electrons to rush back up the wire to let the origin know the conditions have changed at the load end. 

So instead you take a local reference with you, along the same route as the wanted signal,. and measure relative to that.


In many ways the ground is not a level voltage at all, and making the analogy of height and voltage, it behaves more like the floor seems to when you are very drunk, and have to lie down and hang on to it as the room bounces up and down.

Genarally higher frequencies and short pulses aggravate this.


Actually if you have a fast scope, and the ability to generate single fast pulses, you can make a pulse inverter, by cutting some  coax in the middle and wiring the incoming centre to the outgoing ground and vice-versa, and then mounting  it with a couple of coax sockets in a metal box.. Any pulse short compared to the transit time, proportional to the length of the cable (say 2nsec per foot there and back.) does not have time to "know" it is shorted out by the input  and output coax jackets being connected again, and the pulse that sets off as positive on the inner, emerges as negative on the inner. Longer pulses d however see the short circuit, and are truncated.

Quite so - the idea of ground being some magical '0V' is not really true, certainly between points that are far apart in terms of the speeds of the signals in question - there simply is no time for electrons to rush back up the wire to let the origin know the conditions have changed at the load end. 

So instead you take a local reference with you, along the same route as the wanted signal,. and measure relative to that.


In many ways the ground is not a level voltage at all, and making the analogy of height and voltage, it behaves more like the floor seems to when you are very drunk, and have to lie down and hang on to it as the room bounces up and down.

Genarally higher frequencies and short pulses aggravate this.


Actually if you have a fast scope, and the ability to generate single fast pulses, you can make a pulse inverter, by cutting some  coax in the middle and wiring the incoming centre to the outgoing ground and vice-versa, and then mounting  it with a couple of coax sockets in a metal box.. Any pulse short compared to the transit time, proportional to the length of the cable (say 2nsec per foot there and back.) does not have time to "know" it is shorted out by the input  and output coax jackets being connected again, and the pulse that sets off as positive on the inner, emerges as negative on the inner. Longer pulses d however see the short circuit, and are truncated.