Lafayette Radiotelegraphic station - Croix d'Hins - France

History notes (Part 2)

The buildings

The station site includes in addition to the main building a general warehouse, techninal building, restaurant building, coal storage and locomotive garage, personnel buildings (4), school, Station chief house ("the white house"), energy station, water reservoir, garage, gas, pumps room, wood warehouse.

The main building is 76m long, 16m wide and 11m high. It is divided into five machines-rooms. The railway enters in it. More rooms were added after 1938.

When building the parts of main building close to radio equipment, no metal piece was used (including for doors on whatever.  nuts, door handles ... etc) or would be grounded  to avoid heating.

After 1938 a new room was built for new high power lamp transmitter (callsign FYP).
And in 1939 another one was built for lamp-tx shortwave transmitters.
During 1939 was built a new cooling water reservoir and new pumps rooms. The water temperature would be at 25 C in all seasons (dissipating about 100 kW) and staff could swim in it ,although
not officially autorised.

The antenna

The antenna is made of 16 horizontal wires carried by the eight 250m towers  (four towers on each side). The area of this horizontal part is 400 meters x 1200 meters. Then ten wires go down vertically into the main building to the antenna coil. This vertical part is actually the active part of the antenna

The antenna coil is 5 to 6 meters high and same diameter. With the horizontal capacitive part and the ground, the coil constitute the tuned circuit.
Wavelenghts are between 19150 meters to 23450 meters.

The gound system was first a copper plate with an area of 200 square meters burried at 50 centimeters and connected to 100 vertical 14-meters-long copper tubes into the ground.
Then was added a network of 60 kilometers of copper wire burried under the antenna. (you still find some today in the ground)

The transmitter

The spark transmitter : 1920 to 1923
It is built by FEDERAL TELEGRAPH Co.. There are two transmitters in Croix d'Hins, one is a backup. Normal spark power is 1000 kW and the yield to change DC to AC is about 50% leading to 500 kW HF. The spark is fed under 1250 volts and 800 Amperes. Its weight is 80 tons, 70 tons being for the magnetic circuit. That huge cover is 2.8 meters high. Its primary coils is in series with the spark and has the 800 Amperes. It is immerged into oil cooled by the water circuit, pumps and external reservoir. The magnetic field reaches 17000 Gauss. Visitor's watches would often be damaged. Heavy metal pieces lifted more than one meter from the cover would not fall down but would stick to it.
Spark anode is a copper tube one centimeter diameter cooled by water. Cathode is made of carbon, 4 centimeters diameter and 50 centimeters initial length. It is replaced every 24 hours.
It is rotating for a regular erosion. The spark chamber has an atmosphere of alcohol and petroleum (falling drop by drop) to improve efficiency. (20 liters / 24H)

The 1250 volts / 800 amps are obtained from a 1000 kW converter group working under 2200 volts AC coming from the energy building final transformer.

Stabilized spark results in one frequency being transmitted. Morse modulation is obtained by frequency shift. The frequency shift is obtained by short-circuiting one loop in the antenna coil (actually not one of the real loops but 78 smaller loops simultaneously short-circuited. The 78 breakers have silver terminals. They are fed by a 20 kW generator.

The spark transmitter callsign is : LY

Up to 27 harmonics have been found to be generated and these transmitters are causing troubles to others and to the newly introduced radio broadcasting.

From 1923, spark transmitter is kept as backup but replaced by new HF generator, type Bethenod-Latour. (patent by Marius Latour, 1917)
The output power is 500 kW with a 84 percent yield. Its single HF output wavelength is 19150 meters. Its callsign is : FYL

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Go to Part 3

Other references :(thanks Al Heiden, Don Kimberlin)

2020 Updated reference links

- See a description of the station from an online version of "History of communications-Electronics in the United States Navy".
at :   (local copy)

The History of NSS, Annapolis, Maryland   [n.a.]

The Telegraph Office :   [n.a.]

George T. Royden oral history  :  [n.a.]

The Passing of A Pioneer :  [n.a.]

Page by Pierre Dessapt : [n.a.]

Jurassic Telecommunication :

Don Kimberlin's page :  [n.a.]

Informations or documents about Lafayette Station are  welcome at :

Main source : Leaflet by A Nicolazzi, Direction des télécommunications du réseau international  "Croix d'Hins ou historique de "Bordeaux - Lafayette" , 1977

Aug 2000 - 80th anniversary