The next generation of digital STL
Our challenge: to design a studio-to-transmitter link (STL) for your most demanding 950 MHz applications — one as reliable and robust as Harris® Intraplex® T1 and IP audio links. Digital STL manages much more than audio, so installation and configuration need to be straightforward, not a science project. Data should not be optional, requiring additional boxes and complexity. Your STL should be ready, out of the box, for AM, FM and HD Radio™, as well as future multimedia applications. And, of course, the price has to be right.
Earlier digital STLs were not designed for IP data transport. Adding IP data to them required optional modules and external add-ons, and many engineers working on HD Radio installations reported spending much time and money trying to eliminate glitches.
Our solition: HD Link™ is designed to manage all HD Radio™ transport scenarios, regardless of where you place your importer and exporter. Its two prioritized Ethernet paths give preference to HD Radio™ data over control and other LAN/WAN data. It supports both UDP and TCP, and even handles the switching of TCP return packets over asymmetric IP paths with plug-and-play simplicity.
HD Link offers RF power to spare, an integrated IP gateway with sophisticated data handling capabilities, and multiple channels of great audio. The intuitive front panel and remote interfaces tap into the most complete feature set of any micro-wave STL, yet take less time to configure. It can even operate on both RF and IP simultaneously, and allows automatic backup of all services from one to the other.
Intraplex is broadcasting’s first choice for rock-solid, full-time operation of T1 STLs. With HD Link, you can now count on the same dependable performance, superior support and long-term value for your microwave links.
Powerful, reliable RF performance
Designed for data
Top-notch, multichannel audio performance
Easy setup and reliable operation
Convenient connections and display
The ability to do more
Our RF and audio engineering teams designed HD Link for maximum reliability and to carry higher-quality audio and more data over the STL path than was possible with earlier 950 MHz STLs.
As with any Intraplex product, audio quality is a top priority. Uncompressed audio trans-port is fully transparent. In the event bandwidth limitations require audio compression, HD Link offers Enhanced apt-X® coding to prevent the occurrence of audio artifacts that can occur with multiple generations of MPEG compression in the air chain.
Audio and data. And more data.
The architecture of HD Link starts with an integrated IP gateway, the first in a radio STL. This provides you with options for nearly every practical combination of audio, data, control and status used by radio stations — as well as future media applications. With the HD Link system’s 1536 kb/s of allocatable IP data, you’ll no longer consider your STL to be merely an audio transport system that happens to provide some data options. In addition, an asynchronous RS-232 serial data channel accompanies each main program audio channel for use with legacy control systems.
IP done right — the Intraplex way
If you like what Intraplex has done for you with T1 and IP audio and data codecs, you’ll love our implementation in HD Link. The integrated IP gateway includes numerous features:
IP prioritization allows it to carry other IP data, such as control signals and LAN traffic, separately from the high-priority HD Radio stream.
Dual domain access control provides the tightest, most practical security. One access list is for control of the HD Link units. Another manages the firewall that keeps unwanted traffic off the transport link.
Layer 3 switching supports an asymmetric TCP return path, allowing integrated “plug and play” support for TCP wherever a return path exists. Using TCP allows quality HD Radio transport under 30 times higher bit error rate (BER) conditions than UDP (3x 10-4 for TCP versus 10-5 for UDP).
IP tunneling allows TCP return packets with private addresses to traverse third-party networks like ISPs.
HD Link IP Gateway Architecture
How HD Link Technology Improves Link Quality
Like most digital microwave systems, HD Link uses quadrature amplitude modulation to maximize data throughput. All other factors being equal, higher-order QAM can deliver more data using the same RF bandwidth than lower-order QAM (Figure 1), but each step up in QAM order requires about 3 dB to 4 dB better signal-to-noise ratio on the RF link to maintain the same level of quality. RF link quality is thus a critical factor in determining the amount of data that any given 950 MHz STL can carry.
Forward error correction is a useful tool for improving link quality in digital transmission. Essentially, it involves adding redundant data to the transmission stream to allow the detection and reconstruction of missing information. All digital RF STLs use some form of FEC, typically using either the Reed-Solomon or the Viterbi coding method.
However, adding FEC increases the bit rate of the STL. Adding enough extra bits may require the use of a higher QAM order, which places greater demands on the link qual-ity, thereby creating a Catch-22 situation — adding FEC to improve link quality may cause an increase in QAM order, which requires yet higher link quality.
Figure 1. Higher-order QAM levels enable greater data carrying capacity
With HD Link, Harris has taken significant steps to improve this situation.
First, HD Link uses LDPC to do its FEC coding. LDPC is more efficient than either Reed-Solomon or Viterbi, requiring less overhead data to provide the same level of er-ror correction; given the same overhead, it typically provides about 3 dB improvement in link performance over traditional FEC methods (Figure 2). While the mathematical principles underlying LDPC have been understood for some time, only recently have DSP chips become available with the speed and processing power to run LDPC on digital STL signals in real time.
Figure 2. The HD Link system’s advanced error correction handles difficult links
better than STLs using older technology
In addition, whereas the performance of Reed-Solomon FEC falls off directly if the link quality is degraded due to environmental or other interference, LDPC maintains supe-rior performance in the face of link deterioration.
Further, where other STLs add a fixed level of FEC regardless of the system configura-tion, HD Link uses adjustable amounts of FEC and employs a sophisticated algorithm to calculate the optimum balance between QAM order and FEC overhead to achieve the maximum data throughput for any given configuration.
The result? Combined with the increased performance afforded by its 5 W amplifier, HD Link can provide up to 10 dB of system enhancement, right out of the box, compared with older digital STL systems (Figure 3).
Figure 3. The combination of HD Link technology advantages can offer you
a dramatically improved STL system.
Elegantly simple installation, configuration and operation
Your time is valuable, so HD Link is designed to make setup quick and painless. The front-panel display is bright and clear, with easy-to-understand labels. Menu hierar-chies are shallow, so accessing most functions takes only a few steps.
Modem settings automatically synchronize between the transmitter and receiver units. With both units set for the same frequency and RF bandwidth, changes to QAM, IP bandwidth, etc., on the transmitter automatically sync to the receiver.
HD Link has tools to help you in planning your overall STL system. Select the ac-tive audio channels and IP bandwidth you want it to carry, and HD Link automatically calculates the optimum settings for QAM and forward error correction, along with the receive signal strength necessary to achieve the desired level of throughput. These auto-calculated values enable you to prepare a reliable path calculation and determine the requisite transmitter power, antenna size and other variables.
HD Link provides numerous interfaces for setup, diagnostics and updates, with Ether-net and USB ports on each unit, plus remote access via HTTP, FTP and SNMP.
Additional convenience features include a headphone jack and AES/EBU sync port on the receiver, and variable-speed fans to minimize noise. And HD Link is physically com-pact at only two rack units per end.
When your HD Link is connected to a bidirectional IP network with sufficient bandwidth, the program channels will automatically switch to IP should the 950 MHz link fail. In ef-fect, HD Link is both a 950 MHz RF STL and an IP audio STL in one box, with automatic fallback from one to the other.
HD Link Transmitter Rear Panel
Specifications and designs are subject to change without notice.
|Frequency||944 to 960 MHz fully synthesized|
|Step Size||25 kHz|
|Frequency Accuracy||±4 PPM (±0.0004%)|
|Occupied Bandwidth||200/250/300/375/500 kHz|
|FCC Emission Type|
|Designator(s)||200KD7W, 250KD7W, 300KD7W, 500KD7W|
|Modulation||Digital, 32/64/128/256 QAM|
|Antenna Connector||Type N (female), 50 ohms|
|Error Correction Overhead||8 to 25% depending on mode|
|Power||1/2/5 W RMS|
|Monitoring||Forward power, reverse power, VSWR, PLL lock|
|Sensitivity||-95 to -82 dBm depending on mode|
|Dynamic Range||0 to -95 dBm|
|Spurious and Harmonic Equalizer||24-tap feed-forward filter and 3-tap decision feedback filter|
|Monitoring||Receive lock, receive signal level, receive signal-to-noise ratio, PLL lock|
|Delay||Main audio end-to-end delay is 50 to 300 mS based on mode. HD Radio™ and Ethernet end-to-end delay less than 20 mS|
|Networking||Up to 1.5 Mb/s UDP/IP or TCP/IP* transport
(*TCP/IP transport requires an external IP return path)
Three 10/100Base-T, full-duplex, auto-negotiation
1 port for monitoring and remote control
1 port for high-priority data
1 port for low-priority data
|Ethernet Connectors||3 RJ-45, each connector with integrated LEDs for link and activity monitoring|
|Protocols||IP, TCP, UDP, HTTP, FTP, NTP, Syslog, and SNMPv2c|
|IP Gateway||Port or IP based prioritization, static routing, proxy ARP, policing, firewall, public or private network for return path|
|Control and Monitoring|
|Front Panel||Intuitive, graphical front-panel user interface 4.3 in. display, 480x272, TFT Color LCD with LED backlight and 7 button keypad|
|Remote User Interface||Monitoring and control using embedded Web server|
|VU Meter||Front-panel display, 6 segment audio level indicator for all audio channels|
|Contacts, Output||4 output contacts with both normally closed and normally open outputs|
|2 output contacts: normally closed|
|Maximum current: 120 mA|
|Maximum voltage: 350 VDC|
|Closed resistance: 23 ohms typical|
|Contacts, Input||2 input contacts, TTL compatible|
|Telemetry Output||2 analog outputs (0 to 5 V) for RF transmit forward and reverse power (transmitter)|
|2 analog outputs (0 to 5 V) for RF receive signal level and signal/noise ratio (receiver)|
|Contact/Analog Connector||26-pin D Sub and RJ-45|
|USB||1 USB 2.0 port for saving settings and software upgrade|
|Audio Monitoring||1 stereo 1/4 in. headphone jack (receiver)|
|Fault Detection and Logging||Internal log files, SNMP traps, syslog, and automatic upload of log files|
|AUDIO AND SERIAL DATA|
|Channels||1 or 2 stereo program channels, individually configurable for linear or Enhanced apt-X® audio|
|Sample Rate and Audio|
|Bandwidth||48 ks/s for 22.5 kHz operation|
|44.1 ks/s for 20 kHz operation|
|32 ks/s for 15 kHz operation|
|24 ks/s for 12 kHz operation (apt-X)|
|16 ks/s for 7.5 kHz operation (apt-X)|
|Coding||Linear or Enhanced apt-X|
|Sample Size||16-bit (linear)|
|Connectors||Audio Inputs: XLR female on left, right, and digital AES/EBU|
|Audio Outputs: XLR male on left, right, and digital AES/EBU|
|External AES/EBU Input Clock: RJ-11|
|RS-232 Data: RJ-11|
|Digital/Analog Operation||For input, digital/analog auto-detection|
|For output, digital and analog simultaneous|
|Data Channel||RS-232 data transport 9.6 kb/s (linear)|
|RS-232 data transport 1.2, 2.4, 4.8 and 9.6 kb/s, mode dependent (apt-X)|
|Main Digital Audio|
|Accepted Audio Sampling|
|Rates||Accepts any AES/EBU rate between 32 and 48 ks/s (linear)|
|Accepts any AES/EBU rate between 24 and 48 ks/s (apt-X)|
|Rate Conversion||Rate converts any AES/EBU input rate to 48, 44.1 or 32 ks/s. In addition, for apt-X, rate conversion includes 24 and 16 ks/s|
|External Sync (Receive Only)||Accepts external AES/EBU reference signal or RS-422 clock to synchronize output to facility timing|
|Input/Output Impedance||Balanced, 110 ohms ±20%|
|AES/EBU Channel Status||A&B channel status bits are transported|
|Main Analog Audio|
|Audio Frequency Response|
|±0.5 dB||48 ks/s: 1 Hz to 22 kHz|
|44.1 ks/s: 1 Hz to 20.5 kHz|
|32 ks/s: 1 Hz to 15 kHz|
|Audio Full Load Level||9 to +24 dBu|
|Crosstalk||Better than –80 dB|
|Total Distortion||THD+N, less than 0.003% at 1 kHz – 1 dBFS input (linear)|
|THD+N, less than 0.004% at 1 kHz – 1 dBFS input (apt-X)|
|Dynamic Range||Greater than 91 dB (for linear)|
|Greater than 92 dB (16-bit apt-X)|
|Greater than 105 dB (20-bit apt-X)|
|Greater than 110 dB (24-bit apt-X)|
|Input Impedance||Balanced, greater than 10 K ohms|
|Output Impedance||Balanced, less than 52 ohms|
|Test Tone Generator||1004 Hz test tone at -12 dBFS, which is equivalent to +8 dBm input|
|HD Audio||Integrated IP channel for UDP or TCP HD Radio (importer-to-exporter or exporter-to-exciter)|
|Sample Rate and Audio Bandwidth||16 ks/s for 7.5 kHz operation|
|Audio Connectors||Audio Inputs: XLR female|
|Audio Outputs: XLR male|
|Coding||ITU G.722 mode 1|
|Audio Frequency Response||100 to 6400 Hz ±1 dB|
|Data Rate||64 kb/s per active channel|
|Total Distortion||THD+N, less than 0.1% at 1 kHz to 1 dBFS input|
|Dynamic Range||Greater than 65 dB|
|Input Impedance||Balanced, greater than 10 K ohms|
|Output Impedance||Balanced, less than 52 ohms|
|Mechanical and Environmental|
|Dimensions (H X W X D)||2RU: 3.5 x 19 x 14 in. (8.9 x 48.3 x 35.6 cm)|
|EIA rack mountable|
|Weight||Transmitter: 18.5 lbs (8.4 kg)|
|Receiver: 14.5 lbs (6.6 kg)|
|Power Requirements||Universal AC 100 to 240 VAC, 50/60 Hz|
|Power Consumption||Transmitter: 104 W maximum|
|Receiver: 34 W maximum|
|Fuse Protections||2A AC input fuse|
|Cooling||Forced air using variable-speed internal fan|
|Humidity||To 95% non-condensing|
|Operating Temperature||32º to 122º F (0º to 50º C)|
|Regulatory Compliance||FCC Part 15|
|FCC Part 74, subpart E|