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Technology Stocks : LAST MILE TECHNOLOGIES - Let's Discuss Them Here
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To: Frank A. Coluccio who wrote (533)11/30/1996 2:11:00 PM
From: George T. Hawley   of 12823
 
Hi Frank,

ADSL modulation schemes tend to spread the energy across the spectrum of interest, modifying the power spectral density based on whatever equalization algorithm is used. The AMI spectrum is about what you get by taking a Fourier transform of the waveform.

ADSL with 6 Mb/s downstream may use up to 1.1 MHz of bandwidth, depends on the bits/Hz density achieved with the modulation scheme.
I assume that 50 Mb/s would take about 10 times as much bandwidth but I don't know off-hand.

Screened cables, as I recall, were cables that were dedicated to T1 facilities, typically interoffice trunk cables, rather than subscriber loop cables. The screening helps reduce NEXT between the two directions of transmission.

I would guess that untwisted drop pairs would be slightly more efficient antennas for high frequency coupling than twisted pairs but not by much. The dominant coupling, I think, would be common mode and the resulting transverse mode interference would be more a function of how well balanced the drop wires are with respect to ground as well as the terminations on the pair and the inside wire.

Splice points between different gauges of wire will cause reflections to take place but as the inductance and capacitance of pairs of different gauges, at frequencies a few decades above the voice band are approximately the same and dominate the characteristic impedance of the pair, I think such reflections are second order effects.

Sealing current is a different issue. One of the things I like about ADSL as a passband transmission technique, unlike baseband 2B1Q HDSL,is that sharing of the loop with voice both saves copper (a big dollar value) and finesses the sealing current question.

George

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