>Date: Fri, 21 Feb 1997 09:04:00 -0800 (PST) >From: Duane J Marcroft <[email protected]>
Duane, >It's nothing like the effect the Austel complex impedance network has on >THL. The Austel network causes V.34 28.8 bps connect rate (in my designs) >to drop from 82% t0 78%. Adding the circuitry in the DAA to give enough >pre-emphasis for decent return loss causes too much signal loss. This >means transmit signal drive has to be higher to get -10 dB at the line. >The higher drive level makes it difficult (even for the DSP) to get decent >THL. That's really interesting re: the AUSTEL complex impedance! I had a discussion with the (now retired) head of AUSTEL a couple of years ago, and I asked why they didn't just use 600 Ohms resistive (because so many CPE manufacturers have trouble meeting the 15 dB return loss requirement for the complex impedance). He claimed that one important reason for keeping the complex impedence was that it would improve modem performance in the network! ________________________________________________________________ John Combs, Senior Project Engineer, ITS/TestMark Laboratories Email: [email protected] URL: http://www.testmark.com
