IP-based STLs

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Goodbye analog (and some digital) STLs, hello IP

For those who remain unconvinced that there are advantages to using a digital STL, let's consider those specs for just a moment. This type of radio system is carrying the equivalent of what three analog radio systems would carry; at the same time, its audio specs are way beyond what the best analog radio could ever do, and the receiver needs less signal to do it.

Moseley Lanlink and Starlink SL9003Q

Moseley Lanlink and Starlink SL9003Q

In a nutshell, the digital radio systems are way more efficient in terms of the bandwidth they need, along with the amount of power they need, and oh by the way — the audio is better too.

Moseley offers the Starlink SL9003Q, which will also carry up to six channels of digital audio; the bandwidth and modulation scheme depend upon the number of audio channels specified by the end-user. The Starlink has both analog inputs and outputs along with AES inputs (built-in SRC) and outputs. As you would expect from a digital radio, the audio specs are great with a dynamic range of 90dB and a THD spec of less than 0.01 percent. The Starlink can also be configured to use up some of its native bandwidth for a simplex LAN extension which will deliver UDP data streams (up to a total of 544kb/s).

Other configurations

The trend in technology for audio transport (along with most other forms of communication) is certainly more and more based on IP. So, though you may simply need one AES data stream for your analog transmitter, there may very well be many other pieces of gear at the transmitter site that want to communicate with you by means of a LAN. These would include RBDS encoders, remote controls, computers, remote cameras, VoIP phones, satellite receivers, and on and on.

As mentioned above, the Starlink can send UDP data streams to a transmitter site, but most of the items you would place at the transmitter site are going to require a duplex link so they can communicate via TCP (as opposed to UDP). What's the practical way to accomplish that, assuming there are no other options at your transmitter site?

Fortunately for us broadcasters there is the 900MHz ISM band (which actually extends from 902 to 928MHz). Unlicensed channels can be used in this band (subject to FCC parts 18 and 15) for the purpose of carrying digital data, to and from the transmitter site. The relative proximity to the 950 band we're accustomed to using means that we can re-use the antennas already in place easily enough. This is done by adding duplexers to an already established link. (When you fill out the 601 for your new digital STL system make sure you add in the additional loss incurred due to the duplexer on the transmit side.)

Moseley makes a system called Lanlink that works in exactly this fashion. The ISM band transceivers that are the heart of the system can deliver 512kb/s of data, 10base-T Ethernet. (In addition to the Ethernet connection, it also provides two RS-232 serial links that can be configured for a data rate between 1200 and 115,200 baud.)

With the explosion in networking, though, there may be other options for you to check. A quick search online is all that is needed to find other manufacturers of 900MHz ISM band radios that transport Ethernet. You could even avoid the cost of the 900MHz duplexers by purchasing separate antennas for the ISM band. And, obviously with this method, there is no effect upon your current 950MHz system.

Higher ISM bands

So far we've covered the 900MHz ISM band mainly because it was close to our familiar 950MHz STL band. You're probably aware that there are quite a few other ISM bands (2.4, 5.3 and 5.8GHz) and there are multiple manufacturers that make gear for use thereupon. Again, the explosion of networking has had a positive effect for end-users in the sense that there are more and more players making the gear and antennas, since the potential market is so big.

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