WJFK-FM Launches HD Radio Quadcast

June 1, 2010

Harris Field Service Engineer Walter Freeman (left) and WJFK Chief Engineer Jeff Loughridge turn on the transmitter for the first HD4 multicast transmitter tests.

Harris Field Service Engineer Walter Freeman (left) and WJFK Chief Engineer Jeff Loughridge turn on the transmitter for the first HD4 multicast transmitter tests.

CBS Radio has a long history of HD Radio development and support. The company has been committed to digital radio since the early 1990s as one of three founding companies behind USA Digital Radio, the predecessor to iBiquity.

It makes perfect sense from this perspective that CBS Radio recently became the first broadcaster to launch an HD Radio quadcast — a four-channel HD Radio broadcast. WJFK-FM in Washington, DC, was selected as the station and is currently live with four HD Radio channels of mostly live sports talk programming.

The FAN Sports Network offers DC-area sports fans free access to WJFK-FM and signals from three other markets: WJZ-FM Baltimore (HD2), WFAN-AM New York (HD3) and WIP-AM Philadelphia (HD4). Dan Mason, president and CEO of CBS Radio, originated the concept of broadcasting the company's best sports talk programming from around the east coast in the DC market.

To make the concept a reality, WJFK established an IP-based distribution system to push signals from the three remote stations to its studios. WJFK also upgraded its transmission and STL systems to support four HD Radio channels, with a Harris HPX30 transmitter at the core. The overall system enables WJFK to broadcast a sports talk quadcast within the new FCC-approved power level of -14dB, expanding the reach of the HD Radio signals closer to the outer edges of the market.

Remote signal delivery

WJFK studios were initially picking up the three remote signals via each station's online radio stream. The station is implementing an IP-based distribution system to send fully packaged audio programs from the remote stations direct to WJFK studios.

The point-to-point configuration for each remote station includes Barix Instreamer and Exstreamer devices. The Instreamers encode the live signals at the remote stations for streaming over the corporate CBS WAN. The Exstreamers receive and decode the signals at WJFK, and an SAS 32KD audio router picks up the signal for delivery to a Harris FlexStar HDI-100 Importer.

While this configuration is active for all live sports talk programming, the stations occasionally have to switch to alternative programming featuring familiar station talent and shows, as WJFK does not retain rights to broadcast most out-of-market sports games.

Multicast generation

The WJFK system is a somewhat typical HD Radio common amplification transmission configuration. The Harris FlexStar Importer is the first step in generating the HD Radio quadcast. The Importer receives the three HD Radio multicast programs, HD2, HD3 and HD4, as AES audio, where they are compressed, encoded and multiplexed along with the PSD (program service data), into a single IP stream for transport over a T1 link to the Exporter.

WJFK installed FlexStar Importer version 4.3, which integrates core code from iBiquity. This new software code adds a third HD Radio codec to provide HD4 channel capability. An additional configuration was added through the Importer's Administrator application to provide an HD4 channel configuration onto the P3 carrier partition using the MP3 Extended Hybrid mode. An additional Audio Capture Client was also added to the Importer suite to intake the third audio channel.

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The Embedded Importer control screen to access the HD2, HD3 and HD4 streams

The Embedded Importer control screen to access the HD2, HD3 and HD4 streams

The Importer also provides three channels of DTS Neural Audio pre-codec conditioning to optimize the multicast audio for the HD Radio codecs. WJFK uses the extended hybrid mode's P3 partition for an additional 24kb/s of capacity. The station divides its channel bandwidth among the four program streams within the total 120kb/s throughput of the MP3 mode.

WJFK had been using a Moseley StarLink fixed microwave STL system to transport the analog FM channel, main channel HD Radio and HD2 program audio to the transmitter site, along with a Moseley LANLink to transmit data. The StarLink remains in place to transport the main program channel as AES audio.

The station opted for a T1 system to transport the remaining quadcast signals. T1 offered a robust platform to transport multiple HD Radio channels. WJFK purchased and installed Ethernet-to-T1 extenders, which essentially extend the CBS corporate WAN to the transmitter site.

The previous multicast setup had both the Importer and Exporter at the transmitter site. WJFK upgraded and moved the Importer back to the studio to accommodate the quadcast but left the Exporter by the transmitter. To maintain Importer-to-Exporter synchronization (critical to preventing multicast dropouts), a GPS-referenced word clock was connected to the Importer's audio card word-clock input.

The newer FlexStar -200 Embedded Exporter replaced the previous PC-based HDE-100 Exporter. The Exporter takes the incoming audio stream and creates a delayed output for the analog audio input to the Exciter. It also encodes the Main Program Service for the HD Radio main channel, HD1, and multiplexes it with the Importer's incoming multicast IP stream from the Black Box LAN extender.

The HDE-200 Exporter provides an integrated GPS receiver with remote setup and monitoring capabilities, as well as a simpler and more flexible user interface. Its compact size and easier setup process helped to enable a fairly quick installation. WJFK was on the air with the quadcast within days of the transmitter's arrival.

At the transmitter, the main program from the StarLink feeds an Omnia audio processor. There, the main program is split into analog FM audio and MPS digital audio and processed separately. The analog and digital outputs of the Omnia are fed to the analog and digital inputs of the Embedded Exporter.

The Embedded Exporter and the quadcast data stream coming out of the T1 system from the Importer at the studio are connected to an Ethernet data switch along with the FlexStar HDx exciter. From the switch, all four HD Radio program channels flow into the exciter's Exgine where the analog and digital signals are converted into on-channel RF. The RF is then sent to the RF input of the HPX30 transmitter for final amplification.

Transmitter installation and setup

WJFK took advantage of a simultaneous power increase to coincide with the quadcast launch based on the new FCC guidelines that allow HD Radio broadcasters to raise power to -14dB. The station's existing transmitter was incapable of supporting the power increase, and software was not yet available for the existing Importer/Exporter to support four HD Radio channels.

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CBS Market Chief Engineer Jeff Loughridge, Regional Director of Engineering Erich Steinnagel and SVP of Engineering Glynn Walden at the official HD4 launch.

CBS Market Chief Engineer Jeff Loughridge, Regional Director of Engineering Erich Steinnagel and SVP of Engineering Glynn Walden at the official HD4 launch.

The HPX30 transmitter was chosen as it was capable of generating the analog and digital power level needed for WJFK to operate at -14dBc while meeting the 6dB tighter out-of-band emissions requirements established for stations operating at elevated HD Radio power.

Setting up for the -14dB elevated sideband level was relatively easy and straightforward. The level was set up over the GUI screen of the exciter, and the integrated RTAC pre-distortion circuitry automatically made the necessary linearity corrections.

In sizing the output power requirements for the transmitter, it was necessary to account for the additional peak power requirements imposed by the additional Extended Hybrid (MP3 mode) P3 carriers. Using common amplification, the transmitter needed to deliver 13kW of analog power and 621W of digital power to the antenna (which needed no adjustments). That is about 6 percent more digital power than would be required by MP1 mode — well within the capabilities of the HPX30 transmitter. There is also plenty of headroom to raise the HD Radio injection to as high as -10dB if needed in the future.

Signal flow diagram of the WJFK quadcast

Signal flow diagram of the WJFK quadcast. Click image to enlarge.

The entire installation project took less than a week. The transmitter was delivered on a Monday morning to the rigger and to the site on Tuesday morning. The electrical work was performed Tuesday night, and on Wednesday the team connected the Burk remote control and finalized the RF plumbing. The dummy load tests were performed Thursday morning, and the quadcast went on the air that afternoon.

After a weekend of monitoring the system and a brief dark period, the official launch was announced the following week. Harris Field Service Engineer Walter Freeman and Transmission Product Development Manager Tim Anderson were on site to provide assistance throughout the installation and launch. At press time the HD Radio quadcast and supporting technology are both operating flawlessly.

Equipment List

Barix Instreamer and Extstreamer
Black Box LR0301A-KIT
DTS Neural Codec Preconditioner
Harris HPX30, Flexstar HDI-100, Flexstar HDE-200, Flexstar HDE-100
Moseley Starlink, Lanlink
Burk remote control

Walden is SVP engineering, CBS Radio. Loughridge is market director of engineering, CBS Radio, Washington DC.

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