Answer 4—On a spectrum analyzer, a T1 carrying random data looks like a broad hump centered at 772 kHz, tapering down to zero at DC and at 1.544 MHz. There are additional humps with lower amplitudes at higher frequencies that repeat every 1.544 MHz.

To get decent pulse fidelity with little inter-symbol interference, you pretty much need to pass the full frequency range of the first hump. However, simulation shows that an analog passband of 200 to 1,300 kHz (these numbers were picked by eyeballing the raw spectrum of the AMI signal) still gives a fairly decent eye pattern. But if you shave another 100 kHz off each end (300 to 1,200 kHz), the eye pattern really begins to close up.

Contributor: David Tweed