Connecting studio facilities and transmitters

October 1, 2008

32 Avenue of the Americas is home to one of several large Carrier Hotels in New York City, and as such was an advantageous location for our endeavor. “The Hub” as it is known has more than 50 tenants, including AT&T, Verizon, Qwest, XO, and Global Crossing. Obviously this was an advantage to us in choosing a carrier for our communications needs in and out of the building. The Hub itself is on the 24th floor; and since our master control is on the 3rd, it was obvious that some sort of heavy duty interconnection up to the “roof” was called for. Our needs for the build were: a single T3 connection for our Times Square link (backup transmitter site); a single T3 connection for our ESB link (main transmitter site); a single T3 for our WAN connectivity; an OC3 (155 MBPS) to our ISP; a single T3 for our disaster recovery site in New Jersey; and finally seven PRI circuits that would bring in our toll-free number calls from listeners in the tri-state area, as well as our business lines. Our 950MHz STL transmitters (primary backups) would be located on the roof as well; add to that all of our off-air monitoring for the FMs, the HDs, GPS and several of our EAS sources.

Director of Engineering Josh Hadden decided there would be no wirelines to the 24th floor; everything was to be done via fiber. After that decision was taken, he designed the interconnection facilities around two separate systems: the Adtran Opti-6100 system, and the Evertz 7700 frame (more on that below). The Opti-6100 is basically a shelf, into which specific-function modules are installed. The system is then made up of two of the Opti-6100 shelves; one was to be located in MCR and the complementary unit in our racks on the 24th floor. The two 6100s are configured for OC12 operation and connected together via single-mode fibers (one in each direction) operating at 1310nm. Redundancy is a primary design consideration in the Clear Channel New York operation, so our complete system design includes two sets of the 6100s: one for the west riser, and one for the east riser.

Each of the five stations makes use of a Harris/Intraplex DACS 9560 cross-connect as the primary STL. In this way, one encoder board (in this case a PT353) can have its encoded output (timeslots 1 through 23) “copied” and also sent out via an additional port on the DACS. The first port on the 9560 is used to communicate with our main transmitter site at the ESB; the copied port is sent to our backup site at 4 Times Square. A separate DACS frame is used to handle all the five stations remote controls.

The T1 links from the DACS, meant for the ESB, are connected to an Adtran MX2800 DS3 mux/demux. The DS3 link from this particular MX2800 is connected to the Opti-6100 for the west riser, and thereafter connected to the 24th floor. The T1 links from the DACS meant for Times Square are sent to a separate MX2800, and thereafter connected to the 24th floor via the Opti-6100 assigned to the east-riser.

Each MX2800 mulitplexes 28 separate T1s though; and if you were counting, you only got to six. Each transmitter site also has a separate network (each of which is really just a separate subnet of the network used inside the Clear Channel WAN). Quite a bit of data makes its way up to the ESB: RDS, MPS PAD, and SPS PAD for WLTW (Lite FM), WHTZ (Z100), WAXQ (Q104-3) and WWPR (Power 105.1). The entire HD Radio data stream for WKTU gets to the ESB over this same network link. As you would expect there are many computer workstations located at the ESB as well — scattered throughout our four different transmitter rooms on three floors of the Empire State Building (ESB). (Data requirements for our 4 Times Square transmitter site are lighter.) The link for each of the two transmitter sites' networks consists of 16 T1s bundled in to a single PPP connection by way of two sets of Adtran 5305 Routers (one set for the ESB and one set for 4 Times Square).

The actual physical links between 32 Avenue of the Americas and the two transmitter sites are T3s provided by AT&T on the 32 Avenue of the Americas, and Verizon at each of the transmitter site ends. (Obviously they meet up at one of the various central offices located in Manhattan.)

The Evertz system I mentioned earlier also consists of shelves in to which specific-function modules are added. Like the Adtran system, the Evertz shelf in our MCR is connected to its complement on the 24th floor by way of fiber. (All the modules mentioned below have lightwave inputs and/or outputs, and are further muxed/demuxed together via 7705CWDM modules.) The Evertz system is extremely flexible. For example: We make use of a 7707AT-8 module that carries eight separate AES signals up to the roof. Audio processors fed by AES drive our 950MHz STL transmitters, which in turn feed two separate 950 antennas — one located on each of the two towers on top of the building (did I not say redundancy was a primary component of the design?)

So even though we use two separate risers in the building for our fiber runs to the 24 th floor, and even though we have 950MHz radio links as our primary backups, we still considered the possibility that the roof might become disconnected somehow from our MCR. For this reason, we opted to lease the modern-day equivalent of 15kHz stereo lines from Verizon (our local Telco). These circuits are built around the Pulscomm PCAU and each of our five stations has a pair of these lines to each transmitter site — 10 pairs in all. These make up our tertiary STLs, and they are the only egress from the building done at ground level.

32 A/A is only about 2.5 miles south of the ESB (and just slightly farther from 4 Times Square) and since our off-air receive antenna is on top of the building (525' AGL) you would expect that the receive signal level is quite good — and you'd be right. Using a single Scala CLFM we get about -10dBm per carrier from each of the 18 FM signals at the ESB. In order to meet our fiber only system requirement, we used another Evertz module pair — the 7707 IFTA and IFRA. This system accepts RF over a wide bandwidth, converts it to light, runs it over a fiber, and puts RF back out the other end. In this manner we're able to get RF from our analog and HD transmitters from the receive antenna on the roof, and to the MCR. Finally, we make use of a set of 7707GPS modules to get our GPS signals from the roof to MCR, where two Evertz 5600 MSC units feed a 5600ACO, providing redundancy in the generation of all the clock signals we need throughout the facility.

The Clear Channel consolidation project in New York is arguably one of the largest and most complex projects ever taken on by the company. The major design factors for all inbound and outbound communication systems are the number of sites involved and a high level of redundancy for each. A tremendous amount of time and energy went in to the design and implementation of the systems described, and we anticipate the results will benefit the stations for years to come.

Irwin is chief engineer of WKTU, New York.

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