Radiotelegraphy - time signals and weather bulletins

The first activity of Wireless Telegraphy was radiotelegraphy. Transmission was done in Morse code. The messages transmitted from the Eiffel Tower in 1926 carried hourly, meteorological, and scientific information:

• Ordinary time signals (partially automatic)
• Automatic ordinary time signals (international scheme)
• Scientific time signals (rhythmic)
• Meteorological telegrams
• Seismological telegrams
• U. R. S. I. signals (International Scientific Radiotelegraphic Union)
• Emission of calibrated waves

The semi-automatic ordinary time signals give the time with an accuracy of about 1/10 or 1/4 of a second, allowing ships to fix their position and correct their watches. The automatic time signals serve the same purposes as the previous ones. They are sent by a special device installed in the pendulum room of the Paris Observatory. Similar signals are sent by various foreign stations through the International Time Bureau. The emissions are carried out by damped musical waves.
The scientific or rhythmic time signals are made using beats, each of one sidereal second, minus 1/50 of a sidereal second. These beats are listened to at the Paris Observatory and are radiotelegraphed by the station itself. With the help of these indications, it is possible to determine the longitude of a place to within 1/100 of a second, where the local sidereal time is directly determined.

The meteorological telegrams are intended for all those who may be interested in the state of the atmosphere and the immediate details that can be deduced from it, and mainly for ships and airplanes. These bulletins are also of interest to agriculture. The emissions are made by damped musical waves: 60 kilowatts in the antenna, wavelength 2,600 meters. Three types of messages are transmitted:

• synoptic observation messages (Météo France)
• European synoptic observation messages (Météo Europe)
• and general situation and forecast messages

In the case of Météo France radiograms, these begin with the words "Météo France" and the text comprises two parts:

• the first relating to observations
• and the second to soundings.

The first group comprises:

• twenty-five series of five groups of digits for the 7 a.m. observation messages
• and twenty-five series of four groups of digits for the 1 a.m., 1 p.m., and 6 p.m. observation messages.

The other groups are presented as follows:

1st For the 7 a.m. observation:

The other groups are presented as follows:

1st For the 7 a.m. observation:

BBB

DD

F

C

TT

N

b

bb

PP

MM

mm

µ.

2nd For the 1 a.m., 1 p.m., and 6 p.m. observations:
BBBDDFGTTbbb, where: BBB, three digits indicating the pressure in tenths of millimeters; DD, two digits indicating the wind direction according to the following code:

Direction	Code DD	Direction	Code DD	Direction	Code DD
N.	32	S. E.	12	W. S. W.	22
N. N. E.	02	S. S. E.	14	W.	24
N. E.	04	S..........	16	W. N. W.	26
E. N. E.	06	S. S. W.	18	N. W.	28
E.	08	S. W.	20	N. N. W.	30
E. S. E	10

F A digit indicating the wind force in accordance with the following indications:

Speed (m/s)	Code F	Speed (m/s)	Code F	Speed (m/s)	Code F
0  to 1	0	6 to 8.	4	15 to 18	8
1   to 2	l	8 to 10	5	>    18	9
2  to 4	2	10 to 12	6
4 to 6	3	12 to 15	7
0  to 1	0

C. A digit indicating the state of the sky according to the following code:

Sky	Code C	Sky	Code C
Cloudless sky	0	Rain	5
Sky ¼ covered	1	Snow	6
Sky ½ covered	2	Light fog	7
Sky ¾ covered	3	Thick fog Storm	8
Overcast sky	4	Storm	9

T. T. Two digits indicating the temperature in whole degrees. 50 is added to the number when the temperature is negative. For temperatures close to zero, the following has been adopted:

T (°C)	Code TT	T (°C)	Code TT
from 0.1 to 0.4	00	from - 0.4 to - 0.0	50
from 0.5 to 1.4	01	from - 1.4 to - 0.5	51

A digit indicating the direction of the upper clouds (cirrus type), according to the following code:

Clouds coming from	Code N	Clouds coming from	Code N
Observed clouds having no appreciable movement	0	from S.-W.	5
N.-E.	1	W.	6
E	2	from N.-W.	7
from S.-E.	3	from N.	8
from S.	4	No observation.	9

b. A digit indicating the characteristic of the barometric tendency immediately before the observation and according to the following code:

Tendency	Code B	Tendency	Code B
Barometer stationary	0	Stationary then rising	5
Barometer irregular	1	Stationary then falling	6
Rising regularly	2	Falling then stationary	7
Falling	3	Rising then stationary	8
First falling then rising	4	Storm hook	9

bb. Two digits indicating the barometric tendency in millimeters and tenths of a millimeter. If the tendency is negative, 50 is added to the number D. D. indicating the wind direction.
P. P. Two digits indicating the rainfall in millimeters, fallen since 7 a.m. the previous day.
M. M. Two digits indicating the maximum temperature.
m. m. Ditto. Minimum temperature.
(From 7 a.m. the previous day to 7 a.m. on the day of observation in whole degrees.)
µ a digit indicating the state of the sea according to the following code:

State	µ	State	µ	State	µ
Calm	8	Choppy	4	Very rough	8
Very smooth	1	Swell	5	Furious	9
Smooth	2	Heavy swell	6
Slightly choppy	3	Rough	7