Path: utzoo!utgpu!news-server.csri.toronto.edu!mailrus!accuvax.nwu.edu!nucsrl!telecom-request From: "S. E. Grove" Newsgroups: comp.dcom.telecom Subject: Re: Data Access Lines Message-ID: <8283@accuvax.nwu.edu> Date: 25 May 90 18:06:35 GMT Sender: news@accuvax.nwu.edu Reply-To: "S. E. Grove" Organization: Pacific * Bell, San Ramon, CA Lines: 39 Approved: Telecom@eecs.nwu.edu X-Submissions-To: telecom@eecs.nwu.edu X-Administrivia-To: telecom-request@eecs.nwu.edu X-Telecom-Digest: Volume 10, Issue 385, Message 10 of 10 In article <8084@accuvax.nwu.edu> jgro@apldbio.com (Jeremy Grodberg) writes: > Technical Standards for Data Access Lines > Attenuation Distortion (slope) -1 to +3 dB > C-Message Noise 20 dBrnC > Impulse Noise 59 dBrnCO > Relative Delay (1000 to 2604 Hz) 200 usec. SLOPE means no more than 1 db higher than the reference level of 1khz measured with 900 ohms impedance, and no more than 3 db greater loss that the reference. This is measured in the range of 300hz to 3000hz, unless you ask and pay for higher line conditioning, C4 is measured up to 3400hz, if I remember. All my books are in a locker and therefore not available. C-message noise 0 dbrn is equivalent to -65 db (again I am relying on memory, and I haven't lined up data circuits for a living for ten years), the c refers to a weighting filter, calculated to reduce the effect of noise at frequencies that don't effect the data. Impulse noise is noise of very short duration, sometimes unnoticable to the human ear, but at the speed of 9600 Baud a real deterrent. Relative Delay has to do with the delay of various frequencies reaching the terminating modem in reference to the fastest frequency, within the bandwith. The fastest frequency can vary, though it is usually around 2400hz. This could affect the shape of the analog envelope of the signal and make it harder for the detection circuits in the modem to determine space or mark. At 9600 baud you are dealing with a 209 type data set which uses tri bits (000,001,010,011,etc) to reduce the actual line speed and eight phase 'phase modulation'. Stephen Grove Pac Bell, Comm. Tech. ESS; Sonoma County, Calif.