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From: chip@chinacat.unicom.com (Chip Rosenthal)
Newsgroups: comp.dcom.telecom
Subject: Re: Data Access Lines
Message-ID: <8402@accuvax.nwu.edu>
Date: 29 May 90 05:07:40 GMT
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X-Telecom-Digest: Volume 10, Issue 396, Message 1 of 12


John Higdon <john@bovine.ati.com> writes:

>Chip Rosenthal <chip@chinacat.unicom.com> writes:
>> dBm is commonly used to specify a level referenced to a "digital milliwatt"
>> signal.  This is a 1004Hz sine wave of 1mW power into 600ohms.

>What was it before digital technology? I've always heard it referred
>to as simply the "milliwatt".

Of course, you are correct.  dBm is power relative to a milliwatt.  I
slipped into that thinking because the bench work I've always done was
with digital equipment.

>Also, to be technically pure, dBm can be a reference to one milliwatt
>into any impedance, as long as it's a milliwatt.

Right.  The 600ohms is a common impedance, and would be the required
termination if you were to feed the digital milliwatt pattern into,
say a CODEC, and want to really get a milliwatt of power delivered.

>And it is still 0 dBm.

I stand, if not corrected, then at least clarified and unconfused :-)


Chip Rosenthal                           
chip@chinacat.Unicom.COM                 
Unicom Systems Development, 512-482-8260