Myat UHF and VHF combiners receive signals from Harris transmitters below and selectively allow channels to pass through without causing interference to each other.
Redundancy is integral to any modern broadcast facility. And for good reason, considering the growing importance of disaster recovery in broadcasting today. If the main site goes down, having a backup transmission facility at a different site is the best game plan. Broadcasting from a backup site provides a reliable means of reaching at least a large portion, if not all, of the station's coverage area.
Nowhere is the importance of staying on-the-air more apparent than in New York City, where local broadcasters serve millions of viewers. Manhattan remains the best position for broadcasters to reach their viewers over-the-air. However, site choices are limited, especially for rooftop towers.
Recent terrorism events and electricity breakdowns are just two factors that have forced area broadcasters to rethink their backup strategies. Some local stations keep backup transmitters at their main transmission sites. Others have secured separate backup transmission sites to ensure they remain on-the-air in a disaster. Two local broadcasters, WABC-TV and Univision, chose the latter option and secured space at Four Times Square.
Television moves in
The Manhattan skyscraper is owned by The Durst Organization, a real-estate company that develops, owns and manages properties in the NYC area. The company built and opened the building in 1999. The original design featured space for radio transmission and other communications facilities, with an eye toward DTV. The initial design phase included potential for a 200ft rooftop broadcast tower. A 132ft Hemphill tower with a Shively model 6016 master FM antenna provided backup transmission facilities for five local radio stations. An 80ft tower surrounds the broadcast tower for outer ancillary facilities. It features four levels with more than 11,000sq ft of surface area to accommodate microwave communications, two-way radio systems, RPU antennas and STLs.
After Sept. 11 underscored the importance of backup TV transmission facilities, The Durst Organization replaced Four Times Square's existing tower with one that would accommodate all FM radio and TV stations in the city. Univision was the first TV broadcaster to lease space, establishing backup facilities for New York area analog stations WXTV-TV and WFUT-TV. Univision also decided on Four Times Square as the primary location for WFUT's digital channel.
The digital channel went on-air at low power May 1, 2003, and switched to full power on July 13, 2004. The analog channel was ready for air in mid-March 2004. Univision had its first test during the August 2003 citywide blackout. WFUT-DT's temporary low-power DTV transmitter stayed on the air using power generators, showing the importance of back-up plans.
Signal transmission
ABC affiliate WABC leased space at Four Times Square in the summer of 2003 to include backup transmission facilities for its analog channel 7 and digital channel 45. The latter was launched at half-power on Oct. 30, 2003. Full-power operation began in late August 2004. The backup facilities for channel 7 protect the primary site on the Empire State Building.
Harris analog and digital transmitters are used at the Four Times Square retransmission facility, as seen here in the WABC-TV transmitter room. WABC uses a 50kW Platinum series transmitter for its analog channel and a 27.5kW Diamond CD transmitter for its digital station.
Both broadcasters use Harris transmitters for signal transmission. WXTV uses a 50kW Sigma UHF transmitter, and WFUT employs a 100kW Sigma model. A 10.5kW (average power) Diamond CD UHF transmitter is used for WFUT's digital channel. WABC selected a 50kW Platinum Series VHF transmitter for its analog channel and a 27.5kW (average power) Diamond CD transmitter for its digital station.
Multiple-cabinet designs allow different on-air configurations. For instance, WABC's 50kW transmitter features five identical PA cabinets. These provide a high level of redundancy and allow for continuous operation in the event a module, or even an entire cabinet, fails for any reason.
WABC's digital transmitter includes Harris Apex exciters to drive the amplifiers. The exciters convert the SMPTE 310 signal to 8-VSB, while maintaining compliant FCC mask performance and using adaptive correction to improve signal-to-noise ratio (SNR). Self-contained routines perform correction automatically, reducing the need for periodic maintenance adjustments on the exciter level. The exciters can easily be connected to a precise reference to protect against interference between adjacent channels, such as with WFUT-DT.
The Myat combiner system for UHF channels 40 to 60 sends signals to a Dielectric TUA-C8/64-U-2-B-R upper UHF antenna after ensuring that potentially interference-causing signals from other channels have been filtered out during the combining process.
The two facilities are housed in separate areas on the upper mezzanine, located just below the 50th floor. Signals originating from each broadcaster's studio reach the transmission facilities over microwave and fiber. Because the stations' signal paths are similar, this article will use WABC as a model. A Microwave Radio Code-Runner two-way microwave link combines the station's analog and digital microwave signals during transmission. Verizon provides the fiber links: The analog channel is transmitted over a 270Mb/s fiber link, and the digital channel uses a SMPTE 310 19.3Mb/s link. Digital signals from the studio reach a terminal gear rack upon entering the facility. Each exciter is connected to an Evertz switcher that selects the signal that feeds it.
The analog side is slightly more complicated. WABC transmits 601 digital video with embedded audio from the studio. That signal is immediately converted to analog using Fortel conversion gear, which also disembeds the audio. Thomson Grass Valley distribution equipment and processing amplifiers connect to Leitch switchers, which feed analog video and audio sources to the Platinum's dual exciters. The station created room for a “steerable” ENG antenna to establish an emergency link into the transmitter, and to support its news operations.
Fully redundant analog and digital signal paths ensure that no single component failure will take the station off the air. Dual Modulation Sciences STV-784 stereo generators provide audio processing on the NTSC-compliant audio signals.
There is a lag time of six to eight seconds when the load is transferred from the main electrical system to a generator. Both the WABC and Univision racks include UPS equipment to keep the control and processing equipment online while the generator gets up to speed. Four-foot aisles provide fire safety and a comfortable, serviceable environment, with rear access to equipment racks.
Having the same transmitters allows Univision and WABC's transmitters to stock fewer parts by borrowing interchangeable modules from each other, reducing costs while retaining redundancy.
The transmitters route the signals to Myat UHF and VHF combiner modules in the TV combiner room on the 52nd floor through 4-1/16in (analog channels) and 6-1/8in (digital channels) transmission line. The combiners selectively allow channels to pass into and through the system. As the signals are combined, the modules prevent signals from coming back down the transmission line and into a different transmitter's output.
Additional facilities
The four separate combiner systems are designated by frequencies so channel signals are sent to specific antennas before going out to air. At the very top is an Andrew Trasar antenna provided by Univision for channel 68. Two Dielectric UHF antennas are featured directly below: The upper antenna is designated for channels 40 to 60, and the lower for channels 24 to 45. Overlap is provided for the middle frequencies so either antenna could handle them.
Underneath is the Dielectric high-band VHF antenna for channels 7 to 13, with the Shively analog/digital FM master antenna just below. Space is provided further down for a combined channel 4 to 5 antenna and a separate channel 2 antenna.
Three additional floors complete the transmission facilities. The lower mezzanine is available and reserved for additional TV transmitter rooms. Just below the mezzanine levels, the 49th floor houses the building's three emergency generators. Two are reserved for TV and FM tenants (the other is primarily used for building fire and safety purposes). The broadcast-oriented generators provide a redundant power supply for the broadcast tenants. The three units together generate 5.5MW of power.
The chiller plant provides air conditioning to all TV transmitter rooms to keep the equipment functioning at a high level. Univision receives 60 tons of air, and 60 tons of chilled water for the analog transmitters' IOT heat exchangers. WABC gets 50 tons of air. Each licensee was responsible for extending the ductwork from its outlet to provide airflow throughout its space. Maintenance building engineers change filters, monitor the units and provide general HVAC service.
A Harris ReCon control and monitoring system helps keep an eye on the facility's health. It was chosen because both Univision and WABC have ReCon systems.
The system allows one person to monitor the entire facility, either remotely or on-site, through an Internet connection. Once he or she pinpoints a signal problem, an administrator can find the source and fix the problem over the PC. Fault notification can be customized to include e-mails and alarms. All tenants have access to the system, with nine security levels in place to control exactly what each broadcaster can view over the system.
The facility uses the system to monitor everything from terminal gear to antennas. Incidental and reflected power is monitored at the combiner inputs and outputs. Temperature sensors are connected to modules in the TV and FM combiner rooms. Tower beacons and RF monitors on the roof are also connected to the system. Warning lights at all roof access points change green, amber and red depending on RF levels. Additional lights were added to the cooling towers near the FM backup antenna for worker safety.
All of the transmitters feature a control panel. A screen in a remote location provides meters in a different format from the main ReCon terminal. The nitrogen pressurization system for the transmission lines is also connected to the monitoring system. Humidity, pressure and excessive run time are other parameters that are monitored and automatically alarm if outside normal limits. The system creates log notations as the transmitters switch on and off or operate above or below normal (-10 percent to +5 percent) licensed values.
The facility is unique in that the tower design was included from the beginning. With its Manhattan location, plug-and-play design, and room for expansion, Four Times Square is well-positioned to serve NYC broadcasters far into the future.
Equipment list
Harris:
John Lyons is manager of communications and broadcast operations for Four Times Square/The Durst Organization.
HD3050P1 Sigma and HD3100P2 Sigma transmitters
DHD45P2 Diamond CD, HT50HSP Platinum Series and DHD120P4 Diamond CD transmitters
Apex exciters
Dielectric:
ReCon control and monitoring
Microwave Radio CodeRunner
TUA-C8/64U-2-B-R upper UHF antenna
TUA-C8/64U-2-B-R lower UHF antenna
THA-04-6H/24U-1-R high VHF antenna
Andrew Trasar antenna
Myat UHF/VHF combiner modules
Modulation Sciences STV-784 stereo generators
Fortel NTSC conversion gear
Evertz SMPTE 310 switchers
Leitch transmitter switching gear
Design team
Thomson Grass Valley distribution gear and processing amps
Hemphill towers
John Lyons, The Durst Organization/Four Times Square, master antenna system coordination
Bill Beam, WABC-TV
Karl Lahm, Univision
James Lee, ABC/Disney Real Estate and Construction Services
Christiaan Janecka, HLW, Architects
Michael Migliaccio, AMA, electrical/mechanical engineering
Pat Hauserman, Tishman Interiors, GC
Michael Panico, The Systems Group, A/V system integration
Pat Reagan, Harris Broadcast, transmitter system design
Hatzel & Beuhler, specialized RF installation and electrical work
