Delay Lines

[KNSSoftware]

Just watched another good old teardown (EEVblog #985 - Siglent SDS1202X-E Oscilloscope Teardown), and yet again, more reference to delay lines,  In principal i get it; lines the same length to get signal to hit at the time.  What i don't understand is, when i was tough physics, i was always taught the analogy that lines/wires are more like a drinking straw, and electrons in one end, and electrons (further down), pop out the bottom.  If that is the case, why does length matter, as the 'pop out' will happen simultaneously, regardless.

[Nerull]

Because it's not instantaneous - there is a speed of propagation which becomes important when dealing with high frequency signals, where a wavelength or more of different signal levels can exist in the same wire simultaneously.

It would violate the laws of physics for a signal to propagate through a wire instantaneously. You are correct that the signal moves much faster than the electrons within the wire, but the signal still has a speed.

[rstofer]

In the analog scope world, delay lines allow the trace to trigger before the vertical amplifier sees the leading edge.  This allows the scope to display that leading edge.

[T3sl4co1l]

Fluid doesn't move through a straw instantly, why would you think that?   It travels at the speed of sound, at best.  Same thing.

Tim

[Zero999]

Fluid doesn't move through a straw instantly, why would you think that?   It travels at the speed of sound, at best.  Same thing.

Tim

Yes, that's true.

To expand more on that. The speed of electrons travelling through a conductor is very slow, but the changes in voltage/current propagate down the conductor at a much higher speed. When you drink through a straw, the fluid doesn't move anywhere near the speed of sound, however, when you start sucking, the time it takes for the fluid at the other end of the straw to move is much faster, almost the speed of sound, which of course depends on whether the straw is full of water or air.

[bson]

It's not just delay and timing, but the length also affects the standing wave ratio which means they end up with different impedances - Z(w).

[Benta]

It's not just delay and timing, but the length also affects the standing wave ratio which means they end up with different impedances - Z(w).

 

Delay lines are normally impedance matched, so there is full power transfer and no standing waves.

[Mechatrommer]

Fluid doesn't move through a straw instantly, why would you think that?   It travels at the speed of sound, at best.  Same thing.
Tim

Yes, that's true.

it depends on pressure differential between 2 ends, repelling/binding force (density of materials) and the distance between the 2 ends. same with electrons with their voltage differential, imagine people stacked together in a room, when a person on one end push the next, and then the next will push the other next for the cause, until to the other end the propagation of that can be termed as a function of c (speed of light) as its frame of reference. fat people (H2O) propagate slower, thin people propagate faster (electrons). thats how i imagine it.

[Mechatrommer]

Fluid doesn't move through a straw instantly, why would you think that?   It travels at the speed of sound, at best.  Same thing.
Tim

Yes, that's true.

it depends on pressure differential between 2 ends, repelling/binding force (density of materials) and the distance between the 2 ends. same with electrons with their voltage differential, imagine people stacked together in a room, when a person on one end push the next, and then the next will push the other next for the cause, until to the other end the propagation of that can be termed as a function of c (speed of light) as its frame of reference with some "slowing down constant" (0.6, 0.01 whatever). fat people (H2O) propagate slower, thin people propagate faster (electrons). thats how i imagine it.