Electron wrote:
> say I have a signal generator that is generating low frequency pulses wit=
h
> very quick rising/falling times, connected directly to my oscilloscope, a=
nd
> (through a BNC splitter) to a couple of 1 meter long wires (one for signa=
l
> the other for ground), open for now.
>=20
> I can see a nice waveform, which looks as it should.
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> Now I add a capacitor to the end of the 1 meter cable (not a coaxial cabl=
e,
> just 2 wires), and of course the waveform will look distorted, because th=
e
> capacitor is loading the 50 ohm output of the signal generator.
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> BUT if I set the 2 Gsps oscilloscope to measure peak, I can see that just
> after the rising and falling slopes, now that I have added the capacitor
> there have appeared voltage spikes.
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> It doesn't surprise me, but what I cannot be 100% sure of is if these spi=
kes
> are due to transmission line effects (probably they are), or by inductive
> effects (of the cable and/or of the capacitor)?

Short answer: Yes.

Longer answer: A transmission line is simply a pair of conductors with
distributed inductance and capacitance, so in the end, you really have to
consider the lumped effects and the distributed effects together.

For a good introduction, see Robert Lacoste's column in Circuit Cellar -- i=
n
particular:
#223 February 2009, p. 64, Microstrip Techniques
#225 April 2009, p. 50, Time Domain Reflectometry - Detect and Measure
   Impedance Mismatches
#227 June 2009, p. 52, High-Speed Signal Transmission - From Eye Diagrams t=
o
   Preemphasis and Equalization
#245 December 2010, p. 50, Parasitic Components - When Capacitors Behave Li=
ke
   Inductors
#253 August 2011, p. 64, RF and High-Speed PCBs - How to Avoid Basic Mistak=
es=20

I followed up on this topic myself in my EQ quiz in issue #226.
Questions #1 and #2 directly address the situation you're asking about.
#226 May 2009, p. 13, HTML <http://www.circuitcellar.com/eq/226/226.html> T=
est
   Your EQ=20

-- Dave Tweed
--=20
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