Wikipedia
WDPM-DT is a religious television station in Mobile, Alabama, which broadcast locally on UHF channel 23 as an affiliate of the Daystar Television Network. Broadcasting from its transmitter near Robertsdale, Alabama, the station signed on after the analog signal of WSRE ( PBS channel 23) signed off for the last time on February 17, 2009.
Since the "channel 23.1" series of virtual channel designations already identifies the existing PBS member station's digital subchannels, this numbering sequence would not be available to the new station. According to the ATSC standard, WDPM-DT's channel numbers would therefore need to be displayed (using PSIP) using numbering based on WSRE's digital channel number, 31. From sign-on until February 2010, the station displayed as Channel 4.1, which is considered a violation of these standards.