Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!cs.utexas.edu!tut.cis.ohio-state.edu!husc6!m2c!wpi!reynhout
From: reynhout@wpi.wpi.edu (Hagbard Celine)
Newsgroups: sci.electronics
Subject: Re: naive question about RF propagation (anecdote)
Message-ID: <6857@wpi.wpi.edu>
Date: 17 Jan 90 14:05:28 GMT
References: <6671@tekgvs.LABS.TEK.COM>
Reply-To: reynhout@wpi.wpi.edu (Hagbard Celine)
Organization: Worcester Polytechnic Institute, Worcester ,MA
Lines: 30

In article <6671@tekgvs.LABS.TEK.COM> jans@tekgvs.LABS.TEK.COM (Jan Steinman) writes:
>
>"When I drive through a tunnel, FM is okay, but all AM stations suddenly 
>vanish.  What should I do?"
...(He wasn't asking the question, but relating someone else's question.)

   ...which reminds me of something else...  Driving to downtown Boston from
Rhode Island (geographical data given simply because I don't know what tunnel
it is I drove under, what highway I was on, or anything) I drove through a long
underwater tunnel.  I was listening to an AM station's Boston Celtics pregame
show.  When I entered the tunnel, the AM station's signal was immediately
replaced by (I think) a traffic report, obviously very local to the tunnel.
This same broadcast was on EVERY AM frequency.  At the time, I was confused.

   From what I understand now, the AM signal dropped considerably, allowing a
lower-power broadcast at the AM demodulation circuit's RESONANT frequency to
be picked up.  This is done quite intentionally.  For some reason, 660Hz comes
to mind, but this doesn't sound right, and I don't know enough about rf to
say one way or another....but I'm sure someone (almost everyone?) out there
does...

   Any further explanation (assuming that what I have written is even close
to correct) would be appreciated...

   Andrew

-- 
   Andrew Reynhout   (Internet: reynhout@wpi.wpi.edu)
                     (BITNET: reynhout@wpi.bitnet)
   All hail Eris!