Radio in the tunnel
Tue Sep 12 10:42:43 EDT 2006
While driving through the Tip O'Neill Tunnel today and listening to
Air America Radio, I noticed that I had no problem receiving AM 1430
in the tunnel. In fact, I thought the station became slightly
stronger as I entered the tunnel. Does the Big Dig have any sort of
radio repeaters in the tunnel?
Short answer: yes, they do.
Long answer: there was an article in the Globe, I think, about
this...the top 20 stations in the market were chosen and repeated
(probably on a radiating-cable AM/FM system from LPB) in the Big Dig
tunnels. The system doesn't work throughout ALL the tunnels...there's a
few weaker areas; I suspect that part of the tunnel infrastructure only
has one radiating cable (probably Andrew NF2D or a similar cable) for
both tunnels, and Part 15 will only do so much.
WTBU at Boston University uses a RCFM system for their Warren Towers and
West Campus dorms to broadcast on 89.3FM. I believe Bentley College has
a similar system for WBTY.
Anyways, the article was about the minor bit of controversy caused
because someone decided to bump one station in favor of putting WFNX on
the system, which wasn't in the Top 20 of the ratings (presumably the
Arbitron 12+ rankings). IIRC 20 stations is about the realistic limit
these systems can handle; the cable itself can radiate more but the AM &
FM modulators and isolation filters are not cheap.
Audio is, I'm pretty sure, supplied by tuners on the surface somewhere.
I was driving through the tunnels at sunset once while listening to WEEI
and heard the 2-second dropout as they changed to night pattern, even
though I was clearly listening to a rebroadcasted signal (waaaaay too
deep underground to be the actual 850AM signal from Needham)
I've noticed that in some places in the tunnel, WHRB and WERS will come
in. I doubt they're on the re-radiating system, but I guess they're
physically close enough from One Financial Center to penetrate the
ground. WFNX probably does that now, too.
Boston, MA 02246
Fried Bagels - Broadcast Radio & Web
Engineering & Operations Consultant
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