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Goodbye analog (and some digital) STLs, hello IP
Of course the down side to that same explosion is that the potential for interference, even while using the spread-spectrum (frequency-hopping) radios, is real and substantial. Proper engineering of the link will be necessary to minimize the effects of interference from other unlicensed users: highly directional antennas are a must. (Be sure to adjust the TPO of each transmitter so that the ERP remains within legal limits.) Obviously you can also change the polarity of the link to minimize the effects of interference.
Broadcast Electronics makes the Big Pipe LT, which is a radio system that works in the ISM bands mentioned. The entire system is made up of eight components: the program interface (single rack unit that goes in the technical center); a managed Ethernet switch; the IDU (indoor unit) which also goes in the tech center; and finally the ODU (outdoor unit) which mounts near or upon the antenna used on either end. The far end is a duplicate of the near end.
The interface unit has both analog inputs (A/D conversion of up to 24-bit, 96kHz sample rate) and AES inputs (with clock source selectable between its internal clock, AES derived, or word-clock). Additionally, the unit has provision for four GPI/O ins/outs and status, along with an RS-232 data path. By means of the managed Ethernet switch, all the TCP connections necessary for HD Radio (including one representing the analog audio and MPS), the SPS (from a local importer), and the PAD information will be aggregated and trunked over to the IDU. The IDU and ODU are connected by way of a coaxial cable; and finally the ODU communicates with the far end via the selected ISM band RF link. The radio link itself can be managed by way of SNMP, RS-232, HTTP or Telnet.
Perhaps you just want to build a high-bandwidth LAN connection to your transmitter site. After all, you have quite a few choices today in choosing boxes that take audio (analog or digital) in, and put TCP out. As I wrote earlier, almost everything communicates in that fashion today.
Take, for example, the Adtran Tracer series 4205. This radio operates in the 5.8GHz ISM band, and the system consists of only two units — one transceiver on either end. (No IDU/ODU combo.) It has a 50ohm female N output (so plan on using some very good transmission line). The interface for DS-3 data is a 75-ohm BNC so, if you were to elect this type of radio system, you would probably opt to aggregate all of your host TCP sources by means of a managed switch that has a 75-ohm BNC DS-3 interface. The Adtran 5045 is a similar radio system, but includes a built-in Layer 2 switch on both ends, and so obviously the data interface is strictly Ethernet. Both systems are specified to have a maximum TPO of +20dBm, and will achieve a BER of 10-6 with a -78dBm receive level signal.
The options are nearly boundless but for a system that is more economical than the Adtran you may want to consider the Airmux 200 system. Like the other radios I've mentioned, it operates in the high ISM bands. One feature of interest in the Airmux 200 is that in addition to the 100base-T Ethernet port, it has up to two separate T1 inputs; so in the event that T1 must be transported for a legacy TDM system, it can be sent along with the Ethernet transport. The total data throughput of the 200 system is specified at 48Mb/s.
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