In this letter to the editor, the author responds to the story “Tunnel Radio: How Signals Reach Drivers Underground.” Radio World welcomes letters to the editor on this or any story. Email [email protected].
The tunnel article reminded me of the Sepulveda Boulevard tunnel radio situation, in Los Angeles. A section of Sepulveda Boulevard, of which that part is a section of California’s famous Highway 1, extends in a tunnel under two runways and some taxiways of Los Angeles World Airport, LAX.
LAX operated Travelers’ Information Station WNHV296, which originally used 10 watts on 530 kHz. We obtained authorization for operation of WNHV296 with 100 watts, using a Valcom antenna on the south side of Century Boulevard, obtaining a waiver for that power level because LAX occupies such a large area, in order to provide reliable coverage of all the nearby roadways and access routes to the airport.
[Related: “Southern California Cities Invest in AM’s TIS”]
But the Sepulveda tunnel didn’t have adequate signal. So we designed and Burt Weiner constructed a second transmitting facility for the station. When we filed the application for it with the FCC we showed that the antenna was below ground level, which caused FCC to have to modify their software!
The antenna was a single wire suspended a few inches below the tunnel ceiling, and fed from the south end. It provided coverage such that entering and exiting the tunnel was completely transparent – you could not hear the transition, even though the two transmitters were not actually synchronized.
I have attached a scan of the license, which a later LAX administration terminated. I’m told that a successor administration wishes they had not done so.
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