On Thu, 24 Sep 2009 10:57:19 -0700 (PDT), KD7HB
wrote:

Hi, Richard.
I learned of this trick many years ago, 1960's time frame. Portland
drilled a second tunnel through a ridge on West Burnside street,
making it two lanes each direction. Drivers began complaining that
their radio reception always went out when they entered the tunnel.
Duh!!! Everyone said nothing could be done, This was the way radio
worked.

One engineer said he could fix it. They mounted insulators in the
tunnel ceiling, and strung a wire the full length of the tunnel. On
the East side, they ran the wire up somewhere on the hillside. I never
was able to determine just where it went. The antenna picked up the
local am/fm signals and radiated them in the tunnel. Drivers could
continue to listen to the radio when they went into the tunnel. Volume
was reduced sometimes, but reception continued.

I wonder if hf and vhf ham radio operation is possible in the tunnel?

I see the same wire trick in other tunnels. The I-90 tunnels East of
Seattle have the wire.

Paul, KD7HB

Hi Paul,

You can get the same thing going through the tunnel north of the
Golden Gate bridge (this from my experience of 50 years ago).

What these couplings are, for AM at least, are evanescent waves, what
current science calls Plasmons. Others here cut and paste reports of
Tunneling (of the relativistic kind, not the hole in a mountain kind)
- all the same thing, none of which is understood by those who simply
push the copy button on a Xerox.

As the frequency rises, however, it is harder to propagate that energy
90 degrees off the wire unless you are within one quarter to one third
of a wavelength away (which now brings rise to parasitic coupling - as
I said all of this is the same stuff).

73's
Richard Clark, KB7QHC