I have a square wave going through a thousand feet of cable. The cable has \$120 \,\Omega\$ characteristic impedance. I measured the capacitance and inductance of the cable and they are pretty close to the spec sheet.
According to PSpice, the signal I should be getting out the other end of this cable is attenuated but still very much a square wave, only with very minor distortion. What I'm actually seeing is more like a sine wave, it's really rounded and spread out. And it takes a long time for the signal to completely return to zero.
If the cable matches what the spec sheet says, how can it be distorting the signal so much? The cable is twisted shielded pair and I have a \$120 \,\Omega\$ termination. The signal is differential square wave \$\pm 0.8 \,\rm{V}\$ with pulse width of about \$1.4\,\mu \rm{s}\$. Also the cable is currently wrapped on a reel, could that be making a difference? The shield is grounded.
The signal is coming from a MAX942.
EDIT: Thanks for the very detailed responses. I have some more investigating to do.
I'm having trouble commenting on individual answers for some reason, so I am replying in the edit. I have 1000 ft of cable but the goal was 4000 ft and I have been playing with both. 4000 ft of cable is 5.8E-8 Farads. With 120 ohms, the corner frequency is 22 KHZ! Great reply thank you.
I was using the tline lossy in pspice.