98 lines
5.2 KiB
Plaintext
98 lines
5.2 KiB
Plaintext
PIRATE RADIO SURVIVAL GUIDE
|
|
Note: this chapter is from the book "Pirate Radio Survival Guide" written by; Nemesis of
|
|
Radio Doomsday, and Captain Eddy of The Radio Airplane. If you like this book and would
|
|
like to support their efforts, you may send a donation of your choice to either Nemesis or
|
|
Capt. Eddy at PO Box 452, Wellsville NY 14895.
|
|
|
|
Please note that some chapters refer to illistrations or drawings, these could not be included in
|
|
this BBS version of the book. If you would like the illistrations or have other questions you
|
|
may inquire at the above adddress.
|
|
|
|
EVERYTHING YOU WANTED TO KNOW ABOUT G.M.T.
|
|
|
|
|
|
The universal time scale, also known as Greenwich Mean Time or Greenwich Civil
|
|
Time, is based on the mean angle of rotation of the earth about its axis in relation to the sun. It is
|
|
referenced to the prime meridian that passes through Greenwich, England.
|
|
|
|
Since actual solar days vary throughout the year, a mean solar day of 24 hours is used to denote
|
|
one revolution. Determinations of the rotation of the earth relative to the sun are made by
|
|
observing mean sidereal rotation of the earth and converting it to mean solar rotation by
|
|
ephemeris tables based on the accumulated data of many astronomical observatories.
|
|
|
|
Mean solar rotation derived from uncorrected astronomical observations is denoted UT0.
|
|
|
|
Annual variations occur in the speed of rotation of the earth and are probably due to seasonal
|
|
changes in the wind patterns of the Northern and Southern Hemispheres. There is also a
|
|
semiannual variation due chiefly to tidal action of the sun, which distorts the shape of the earth
|
|
slightly. The cumulative effect of these variations is that the earth is late about 30 milliseconds or
|
|
0.45 arc second near June 1, and is ahead about 30 milliseconds or 0.45 arc
|
|
second near October 1 each year. When UT0 is corrected for these periodic variations, it is
|
|
denoted UT1.
|
|
|
|
Irregular variations in the speed of rotation of the earth also occur. These may be due to turbulent
|
|
motions in the core of the earth. In addition, friction of the ocean tides causes a decrease in speed
|
|
of about one millisecond per century. Observations of these effects throughout the world are
|
|
reported to the Bureau International de l'Heure at Paris, which issues corrections to UT1 to
|
|
establish UT2.
|
|
|
|
"Standard Times" are based on UT1 or on UT2.
|
|
|
|
The world is divided into 24 zones, each 15 degrees of longitude, or 1 hour angle, apart. The
|
|
meridian of Greenwich, England, is the center of the zero zone, which extends to 7.5 degrees east
|
|
and west. Proceeding eastward from Greenwich, the zones are numbered 1 to 12 with the prefix
|
|
"plus" to indicate the hour angle to be added to universal time to obtain local "standard time".
|
|
Proceeding westward, the zones are numbered 1 to 12 with the prefix "minus" to
|
|
indicate the hour angle to be subtracted from universal time to obtain local "standard time". For
|
|
example, Washington, DC, at longitude 77 degrees West, is in time zone -5.
|
|
|
|
Actual boundaries of time zones are defined by law or custom and generally do not coincide with
|
|
the theoretical zone, even in some places at sea. In many areas, local legal "standard time" differs
|
|
by 60 or 30 minutes from theoretical standard time.
|
|
|
|
|
|
|
|
|
|
|
|
Note the above does not take into account "daylight savings time" or "summer hours". These are
|
|
purely set by custom or law, and vary from country to country.
|
|
|
|
WWV and Universal Time.
|
|
|
|
WWV and WWVH broadcast voice announcements of Coordinated Universal Time (UTC)
|
|
each minute. The reference time scale is the Coordinated Time Scale maintained by the National
|
|
Institute of Standards and Technology (NIST), formerly the National Bureau of Standards. The
|
|
UTC(NIST/NBS) scale includes small frequency offsets relative to the NIST primary frequency
|
|
standard for coordination purposes.
|
|
|
|
The 24-hour system is used. Numbering starts with 0000 for midnight at the Greenwich Meridian
|
|
(longitude zero). The first two figures give the hour, and the last two figures give the number of
|
|
minutes past the hour when the next .8 second tone begins after the announcement.
|
|
|
|
Prior to 1/1/72, time signals broadcast from WWV and WWVH were kept in close agreement
|
|
with UT2 (astronomical time) by making adjustments of 100 milliseconds as necessary. On
|
|
December 31, 1971, the UTC (NIST/NBS) scale was retarded 0.01076 second to give it an initial
|
|
difference of exactly 10 seconds late with respect to the International Atomic Time (TAI) scale as
|
|
maintained by the Bureau International d l'Heure (BIH).
|
|
|
|
Since the new UTC rate (effective January 1, 1972) is no longer adjusted periodically to agree
|
|
with the rotation rate of the earth, UTC departs more rapidly than before from earth rotation time
|
|
(UT1), gaining about 1 second per year. Corrections to UTC are now made in step adjustments of
|
|
exactly 1 second (called a leap second), as directed by BIH. The leap second adjustments ensure
|
|
that UTC signals as broadcast never differ from UT1 by more than about +0.7 second.
|
|
Corrections no longer relate to UT2.
|
|
|
|
P.R.S.G. Notes: 99% of all Shortwave Listeners use GMT time. You should learn how to use
|
|
GMT correctly, REMEMBER TO ADVANCE THE DATE AFTER 2359!
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|