Doug Lung / RF Report
FCC Permits Use of FXE and FXD Digital Emissions for RPU Operations
CBS station group granted waiver after no interference found
Section 74.462 of the FCC rules limit VHF above 160 MHz and UHF frequency or phase modulated BAS remote pickup (RPU) licenses to digital emission types F1A, F1B, F1D, F1E, F2A, F2B, F2D, and F2E. However, CBS Television Stations, licensee of KCNC-TV in Denver, was able to obtain an experimental license to test FXD and FXE emissions in the UHF BAS band.
After no interference was found from this experimental operation, CBS requested a waiver of Section 74.462 to allow it to use these emission types under Part 74 of the FCC’s Rules and Regulations. (FXD and FXE emissions are used in Motorola's MOTOTRBO system.)
In the letter granting the waiver, John Schauble, Deputy, Broadband Division, Wireless Telecommunications Bureau stated: "We also agree with CBS that it is in the public interest to grant its waiver request. CBS persuasively argues that Station KPF238 would more efficiently use spectrum if it is operated using digital modulation rather than analog modulation. For instance, the use of digital equipment will enable CBS to transmit both voice and data with a single 12.5 kHz channel, which cannot be done when the station is operating in analog mode. And the digital operation of Station KPF238 will also permit CBS to track news gathering vehicles and transmit crucial data, such as text messages and cueing information among station news personnel. Thus, we find that CBS has shown that it is in the public interest to operate Station KPF238 using digital modulation and emission designations FXE and FXD."
The CBS experimental license application for WG2XBM
shows the transmitting equipment includes Motorola XPR6550, XPR4550 and XPR8400 radios. The license specifies radio output powers of 40 watts in both the 450 MHz and 455 MHz BAS RPU bands using 7K60FXE (voice/data) and 7K60FXD (data only) emissions.
The CBS experimental license application indicated that one of the goals of the tests would be to determine if the latency using digital modulation was low enough to allow use in conjunction with live broadcasts.
(The FXE emission designator, decoded using the tables in Section 2.201 of the FCC rules, refers to an emission in which the main carrier is angle modulated (F), the nature of the signals modulating the main carrier are "cases not otherwise defined" (X), and the type of information to be transmitted is "telephony (including sound broadcasting)" (E). The "D" in FXD emission stands for "data transmission, telemetry, telecommand".)