Broadcast Solutions Electronics - Road Tunnel FM Radio Systems

Broadcast Solutions Electronics (BSE) specialises in the design, supply and installation of FM radio transmitter systems. The company manufactures FM radio transmitters from 10mW to 5kW and is one of the few manufacturers that supply all-in-one FM translator units.

TRTX12 IN-TUNNEL REBROADCAST SYSTEM

The TRTX12 is a recently launched 12-channel FM in-tunnel rebroadcast system, which can receive up to 12 FM radio stations and rebroadcast these, on the same frequency, into two tubes of a road-tunnel system via leaky feeders or other transmission mediums.

This allows motorists from either direction to continue to listen in the tunnel to the same radio station that they were before entering.

The system includes an audio break-in facility for emergency announcements. This can be addressed from a control room, with audio announcements able to be selected in one tunnel, on all radio stations, or both.

The system can be expanded from one channel to 12 channels or more with the addition of combiners, splitters and translators.

The combined output of the translators can be connected directly to a 25W linear FM-band amplifier which provides 2W per channel (12 O/Ps), and coupled into the leaky-feeder cable for a particular tunnel.

If the distance to the cable coupling-point is considerable, a fibre-optic modulator, fibre-optic cable and demodulator can be used between the translator's combined output and the linear amplifier in the tunnel. Multiple amplifiers in long tunnels can be placed in sections of cable.

The flexibility of the system is achieved through the selection of a number of different receiver splitter inputs and FM translators, and an equivalent number of transmitter combiner inputs and linear amplifiers.

FM TRANSLATOR PERFORMANCE

The FM translator's performance is that of a high-end system with exceptional audio-distortion, signal to noise and spurious specifications. The translator has a bandwidth of 100kHz, allowing RDS and SCA sub-carriers to be rebroadcast.

FEATURES OF THE TRTX12 REBROADCAST SYSTEM

• Two, four, six, eight, ten or 12-way receiver splitters with band-pass filter
• TR1-01 10mW O/P FM translator with dual O/P and two BIF I / P
• Two, four, six, eight, ten or 12-way low-power RF combiner
• 25W 88MHz to 108MHz band linear-amplifier
• Superior audio-performance
• Dual-transmitter outputs
• Baseband of 100kHz, rebroadcast of RDS and SCA sub-carriers
• Re-insertion of RDS on any channel
• TR1-01 10mW FM translator module with dual-amplifier output and BIF input and control
• Dual six-way receiver splitter with band-pass filters
• -10°C to +50°C operating temperature
• 230V / 50Hz or 115V / 60Hz AC-power input

To reduce the number and level of the inter-modulation products on the output, care must be taken in the selection of the number of channels and the frequencies used. BSE can assist with this planning.

TR1-01 TRANSLATOR SPECIFICATIONS

• Frequency range: 87.5MHz to 108MHz
• RF output power: 10mW
• RF spurious emission: <-65dBc
• RF harmonics: <-65dBc
• Asynchronous AM: <-60dB (filtered 20Hz to 20kHz)
• Synchronous AM: <-60dB (filtered 20Hz to 20kHz)
• Frequency synthesizer: PLL (direct modulation)
• Frequency steps: 100kHz (local)
• Carrier stability: ±2ppm
• Frequency deviation: ±75kHz peak
• RF output connector: N-type (female) 50ohm
• RF monitor connector: BNC 50 ohm
• BIF audio I/P: 24dB
• Input impedance: 10kilohm
• Connector: XLR / F
• Mains consumption: 20VA

RECEIVER SPECIFICATION

The TRTX12's receiver has a frequency range of 87.5MHz to 108MHz with 100kHz steps; -50dBm to -10dBm input level; more than 50dB 30Hz to 15kHz 100% modulation stereo-separation; stereo cross-talk of more than 45dB at 400Hz; stereo distortion better than 0.2%; and a frequency response of ±0.1dB (decoded).

LA-4 LINEAR FM POWER-AMPLIFIER SPECIFICATIONS

• Input / output impedance: 50ohms
• Input / output return-loss: better than 20dB

FM TRANSLATOR / TRANSMITTER OVERALL RESPONSE

• Frequency response: ±20dB 30Hz to 15kHz (decoded)
• THD: <0.2% 400Hz modulation <0.2% 30Hz to 15kHz 100%Hz modulation (decoded)
• S/N: -65dB wideband -65dB 50uS at decoded 30Hz to 15kHz
• Stereo separation: -50dB 30Hz to 15kHz (decoded)

CUSTOMISED RADIO TRANSMITTER SYSTEMS

BSE can also supply complete turn-key systems or modules for integration into customer-designed systems, and full-system engineering capability to design in-tunnel rebroadcast systems to custom requirements.