radio transmissions for the north atlantic

From: (Phillip Espinasse)
Date:         04 Mar 93 19:45:12 PST
Organization: Northwestern University, Evanston Illinois.
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last year i got to visit the atc control center at Shannon.Being
myself a fan of commercial airlines and everything that deals with
them i want to share what i have learned.

vhf is used, as you all know, for atc purposes over land and depends
on 'line of sight' between transmitters and receivers. relay stations
troughout the uk and europe are required to enable transmissions
during flight. over the atlantic, short wave radio is used(HF). Also
because of the limitations of radar, none of the aircraft over the
ocean are tracked estimated times quoted in flight plans, to ensure
that aircraft are kept apart by minimum prescribed limits.

For air traffic purposes the north atlantic is divided into five main
areas: Shanwick, Santa Maria, Iceland, Gander and New York known as
Nartel (the north atlantic radiotelephony network).

My question to you is the following :

i have never been able to find any sort of HF frequency for the north
atlantic boundaries. if ever you know any, i would appreciate it if
you could e-mail me them.  i also would like to know where the major
atc control centers are located in the world.

Student at Northwestern University