Digital milliwatt
{{Short description|Test signal in telecommunications}}
| class="wikitable" style="float:right; text-align: center;"
|+ Code sequence of the digital milliwatt in μ-law and A-law encodings. ! scope="col" rowspan=2 | Word ! scope="col" colspan=2 | Hexadecimal code | |
| scope="col" | μ-law | scope="col" | A-law |
|---|---|
| scope="row" | 1
| {{mono|1e}} || {{mono|34}} | |
| scope="row" | 2
| {{mono|0b}} || {{mono|21}} | |
| scope="row" | 3
| {{mono|0b}} || {{mono|21}} | |
| scope="row" | 4
| {{mono|1e}} || {{mono|34}} | |
| scope="row" | 5
| {{mono|9e}} || {{mono|b4}} | |
| scope="row" | 6
| {{mono|8b}} || {{mono|a1}} | |
| scope="row" | 7
| {{mono|8b}} || {{mono|a1}} | |
| scope="row" | 8
| {{mono|9e}} || {{mono|b4}} |
In digital telephony, the digital milliwatt is a standard test signal that serves as a reference for analog signal levels in the telecommunications network.Anttalainen T., Introduction to Telecommunications Network Engineering, Artech House (2003). When decoding the digital milliwatt, a PCM decoder produces a sinusoidal signal with a frequency of {{val|1|ul=kHz}} with one milliwatt in power ({{val|0|ul=dBm}}, a reference for dBm0).
The digital milliwatt signal is encoded by eight 8-bit words corresponding to one pulse-code modulated cycle of the signal, sampled 8000 times per second. It is typically stored in read-only memory (ROM) in the telecommunication equipment.AT&T, Digital Channel Bank Requirements And Objectives, Publication No. 43801 (December 1978). page A6.
The digital milliwatt signal is often generated in instruments in place of separate test equipment. It has the advantage of being tied in frequency and amplitude to the relatively stable digital clock signal and power (voltage) supply, respectively, that are used by the digital channel bank.