Field Report: WorldCast Systems APT WorldNet Oslo

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While the system came with a basic configuration, I added optional alarms. The frame has seven form-C relays that correspond to the alarms. I assigned one relay to silence on a particular audio module (we use five), one relay to report critical alarms such as a power supply failure or loss of IP on the IP transport card, and another alarm that reports loss of AES on any of the five inputs to the frame. On the far end we program silence sensors. The audio threshold levels and the delay time are adjustable parameters.

IP-based audio transmission

As I mentioned earlier, we use Oslo for our main STL systems between our HQ in the Tribeca neighborhood of NY and our main transmitter sites at the Empire State Building. We also have a complete backup facility for each of the five FMs at 4 Times Square, and we have another complete Oslo system, identical to our Empire system, for our backup site. In each case, the Oslo frames talk via IP. Our sites are connected via T3 data circuits. We use Adtran MX2800s to mux 28 T1s together into the T3 data format. 16 of the 28 T1s are assigned to connect two Adtran 5305 routers — one in our master control and one at the far end. In the configuration of the Adtran routers I have made two networks: one that we use for a remote LAN (7 T1s worth of data) and the other for Oslo (9 T1s worth of data). In that way, Oslo has its own, non-contentious network. We connect Oslo to the Adtran directly via an Ethernet crossover on both ends.

I will note that Oslo is designed to work just fine over a shared network, and has parameters that can be reconfigured by the user (if necessary) to compensate for the particulars of the IP network.

We are fortunate though to have the network completely under our control, end to end. And that control pays dividends: The performance of Oslo over this network is identical to its performance with an Ethernet crossover cable connecting the two frames together. Via the GUI, you can drill down into the performance monitoring to see how well the system is doing. As I write this, I'm looking at our own performance monitoring, and there are four streams (linear, 48kHz sample rate, 24-bit word length) that have each sent more than 750 million packets, with zero loss. The fifth stream has lost a grand total of two packets.

Worldcast Systems

It's been my experience that the audio quality of devices built by APT is unsurpassed, and Oslo is no different. It's a real pleasure to listen to. The unit is built extremely well, and I have the utmost confidence in it. I have had questions for factory service, and APT is very attentive to its customer base.

Irwin is transmission systems supervisor for Clear Channel NYC and chief engineer of WKTU, New York. Contact him at

Editor's note: Field Reports are an exclusive Radio magazine feature for radio broadcasters. Each report is prepared by well-qualified staff at a radio station, production facility or consulting company.

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