REIMS, France — In the north and east of France, Sanef Tolling disseminates traffic information across approximately 2,000 kilometers of motorways to inform daily listeners of accidents, roadwork and congestion among other news related to traffic flow. Launched in 1994 and available on 107.7 MHz FM, the group has long relied on leased E1 lines to transport program audio to transmitters along the route.
The rising costs of supporting an E1 network of this magnitude — in part due to the ongoing expense of leased line and escalating rarity of replacement modules — has influenced Sanef, like many broadcasters, to look to the IP network for cost and maintenance reductions.
The new single-frequency network covers 35 sites, with distances of between 5 to 10 kilometers between each tower.
A compact enclosure at the base of each tower houses the transmitter, auxiliary RF, power and networking equipment, including the Intraplex gear that time-locks the FM signal across the entire SFN.
CHALLENGES
It didn’t take long for Sanef to dive in: Over the summer, Sanef transitioned 10 percent of its E1 transport architecture to an IP-based single-frequency network covering 35 transmission sites. Designed and integrated by STIC, which specializes in broadcast and telecommunications systems for French motorways. The success of the initial phase will likely accelerate expansion of the system to cover the remaining 1,800 kilometers and a total of 150 transmission sites.
In addition to transitioning to an IP-based SFN, the STIC team was tasked with improving stability of the signal for stereo and RDS subcarriers. Sanef also required that the traffic service remain on the air throughout the transition given the critical service the broadcast providers to drivers.
“We had several challenges presented to us from the outset,” said Guy LeMarc, general director, STIC. “The service could not be interrupted, and Sanef required an AES192 digital stream to ensure the best possible quality. We were also challenged with delivering additional RDS information, including the names and titles of broadcast artists along with display of the brand, Sanef 107.7. Above all, it was about improving the comfort level for listeners and availability of the service compared to the older system, which was quickly growing obsolete.”
With these requirements in mind, the STIC team researched options for network-based signal transport. To simultaneously improve signal quality and reduce costs, LeMarc and his colleague Guillaume Faure set their sights on an MPX architecture. This would allow them to centralize all transport and processing equipment at the studio.
The STIC team prepared all equipment rack integration prior to shipment to each of the 35 transmission sites.
“At the studio level, the use of MPX outputs on sound processing equipment makes it possible to offer a much wider range of settings than the use of conventional audio outputs,” said Faure, who serves as project manager for STIC. “It also offers much better control for filling the RF spectrum. And since everything is generated once at a central studio, there is no requirement for special settings at each transmission site.”
With that in mind, STIC designed a point-to-multipoint system using the Intraplex IP Link 100p from GatesAir, which supports AES192 digital composite signal transport over IP as a complete multiplex FM signal containing all RDS data.
A peek inside the rack shows the Ecreso transmitter connected to the GatesAir Intraplex IP Link 100p with plenty of open space below the units to accommodate airflow.
Directional antennas provide a robust front-to-back ratio in excess of 30 dB.
THE NETWORK
Within the codecs, the signal’s error correction process, in the form of dynamic stream splicing, eliminates artifacts from the stream by replacing dropped packets across redundant streams. Security applications are robust to protect on-air signals, with secure SSL web access and support for SNMP Version 3, which enhances encryption and authentication. The codec’s integrated SynchroCast technology also supports dynamically managed delay across the network — a critical need for properly timed signal delivery across all transmitters.
STIC’s broad array of services covered the installation from start to finish, beginning with site and network studies; and ending with integration of commissioning of a turnkey SFN system. This included the outlay of a high-speed MPLS-based fiber-optic network to support AES192 transport, and also enable a smooth transition to the IP service without interrupting on-air services. STIC also installed RFE filters and directional antennas for RF support at each site.
“The use of dual-cavity output filters and a radiation detector to control occupancy of the FM spectrum has been crucial to eliminating pollution of neighboring frequencies,” said LeMarc. “This is especially important for adjacent frequencies used by civil aviation agencies.”
The two program audio signals — one main service, one emergency radio service with hourly cut-ins – originate from the Sanef studio based in Senlis in the Oise, and the transmitter sites are spaced at distances of 5 to 10 kilometers apart. Each of the Ecreso transmitters includes MPX AES inputs to receive the synchronized signals; the carrier is also adjusted thanks to a 10 MHz signal coming from a GPS receiver. The outputs of the amplifiers range from 10 to 100 watts depending on the area covered across each section of the motorway.
Transmission sites are mainly located just off the motorway to enable quick easy access for maintenance and support.
All signal processing and generation for the SFN is consolidated at the main studio.
Faure notes that the efficiency of the SFN is significantly enhanced using GatesAir’s SynchroCast simulcast system.
“The synchronization function within the IP Link allowed us to free ourselves from the calculations of the delay times due to the efficiency and reliability of the signal transport,” he said. “The integrated GPS receiver option with SynchroCast also make it possible to simplify cabling within each transmitter cabinet. And it’s very simple to enter the time delay into the system, and modify it in alignment with network settings. That results in rock-solid stability.”
LeMarc shares that they use an UIT scale to measure signal quality: a score of 5 means a perfect reception, 1 means a very poor sound quality.
“Operationally, we have improved from an average of 4.53 out of 5 to a score of 4.91 out of 5 across this 200-kilometer axis,” added LeMarc. “Intersite connections have been considerably reduced, which is a major contributor to quality and reliability improvements of the perceived signal.”
The directional antennas at each site are also performing strongly, with a robust front-to-back ratio greater than 30 dB.
On the security front, “Sanef is very satisfied with the signal quality and operational cost reduction associated with this new network, which we believe is one of the largest IP-based SFN deployments in radio to date,” said LeMarc. “Should the remaining 1,800 kilometers comprise the same technologies, scaling the system to function in the same manner will be quite seamless.”
Claudia Kienzle is a freelance media technology writer specializing in technology and trends.
