GL Communications Inc.
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A System-wide Radio Project for Massachusetts Bay Transportation Authority (MBTA)

GL conducted propagation studies for a system wide radio project for MBTA that included detailed link budget analysis for tunnel segments and aboveground. Our studies helped MBTA assess the potential for success of radio communications within the service area including:

  • Field Testing and RF coverage prediction of median receive signal level to compare the 470 MHz and 821 MHz bands available to the MBTA
  • Assessment of the need for additional repeater sites inside I-495 and along the commuter rail line corridors
  • Recommendation for strategic radio sites in the Metropolitan Boston Area for optimal coverage
  • Design of the RF interface methodology for providing coverage in the tunnels and below grade elevated sections
  • Analysis of potential for inter-modulation interference at the proposed sites
  • Development of an overall RF coverage criterion to be used for system procurement


Typical Link Budget Calculation For 470 MHZ
Coverage for a typical section Downlink Uplink
Tx Output Power (10W Base and 2W Portable) 40 dBm 33 dBm
Coax Jumper Loss -1.5 dB -1.5 dB
Power Splitter Loss -3.5 dB -3.5 dB
Feeder and DC Block -1.0 dB -1.0 dB
Cable Attenuation for 2650' 1" Radiax -23 dB -23 dB
Coupling Loss for 1" Radiax (includes correction factor) -72 dB -72 dB
Portable Antenna Loss -6 dB -6 dB
Train Blockage -4 dB -4 dB
Body Blockage -6 dB None
Rx Input Power from Above @Receiver Port -77 dBm -78 dBm
Minimum Acceptable Signal for 95% Coverage -90 dBm -90 dBm
System Margin 13 dB 12 dB
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