The station OTCF, type 1939, is the last born of the apparatuses of TSF which equip the Maginot Line in 1940. It is to say if it is interesting to study, would be this only to have an idea about the role that the French high command of the time intends to make play radio. Indeed, the degree of technicality of a material is often closely related to the interest that one carries to him.
The second interest of station OTCF is personal. During his research, the Colonel of the Genious Philippe Truttmann (known of all the amateurs of fortification) not having succeeded in unearthing significant information on station OTCF, it was trying, for his son Michel and myself, to take up the challenge. We had finally the chance to cross of them some traces of which we make you share. (R.Cima)
Station OTCF 1939 (Very Short Waves of Fortress), material of fortress, is a Émetteur-récepteur station, transportable [because of its compactness], but not transportable [unusable by infantrymen moving because of its consequent food]. Its exploitation is done only in phone, over all wavelengths ranging between 4m and 7,5m. Its normal employment is in station-with-station, the use in network is completely exceptional.
Station OTCF is used:
- is for the connections of work to work;
- is to ensure of the connections between works of the PR and troops of interval, or all external elements equipped with material ER40 or ER41;
- is for the connection between work and plane.
Presentation of station OTCF
Dimensions of the station: 42 X 26 X 20cm. The buttons of right-hand side are reserved for the emission, those of left are for the reception.
The microphone (on the right) is suspended with an bracket. The center two sites for cards jack make it possible to use two helmets ear-phones simultaneously (one of them is in place). On the left the sons of food are to be connected to a primary battery.
Food. If the compactness of the apparatus makes it portable, its electricity supply, medieval and cumbersome, prohibits to him to be portable. Indeed, one sees foot soldiers badly making movement with the batteries of a OTCF!
Antenna and site of station OTCF in a fortification
Station OTCF must be connected to an antenna by means of a feeder consisted a cable (electric wire light) twisted (to prevent that it does not make antenna) with two drivers, of which the length cannot exceed 15m approximately, because beyond 15m the losses of power on line become too important. However the antenna must be outside the fortification because the frequencies used do not cross the reinforced concrete. All this to say that station OTCF, in spite of its portability, cannot be installed anywhere. It must be positioned close to outside. This does not pose any main issue if it is not the fact that it would have been preferable that this kind of material is directly easy to handle by the officers of the PC, generally far from surface. One can, indeed, suppose that the latter need to converse on line, for example with a reconnaissance aircraft or troops moving, would be this only to regulate a shooting.
The antenna is a mast dipole of 2,5m top, assembled to residence outside the work, which obliges to install the station in a given room and, in theory, always the same one.
The shape and the orientation of the antenna are imposed by the technological choices. Any antenna is directing and selective. According to its form and its position it radiates (or receives) in privileged directions and filters certain wavelengths. In other words, more the antenna is adapted to the situation plus it provides useful output. Thus must it have a geometry and an orientation all the more imperative as the apparatus on which it is connected is of low power.
The solution adopted for the OTCF is simplest that it is. The antenna, linear with two bits (mast dipole), is called half-wave because with its 2,5m length it is intrinsically granted on the waves of 5m (60MHz) that it selects in a preferential way.
Moreover, so that the waves used are not strongly absorbed and are not attenuated by the ground, the bits of the antenna are perpendicular on the ground (horizontal bits collect the waves badly).
On this photograph one sees the fixed antenna, places from there on the wall of the casemate of the Bridge Saint Louis (It is vertical, on the left crenel for gun of 37mm). The photographs of antenna OTCF in place are extremely rare! This one, one owes it to the corporal Lucien Robert (member of the crew of the Bridge Saint Louis in 1940). It took it on June 25th, 1940, day of the coming into effect of the armistice and entrusted it to Michel Truttmann. We published it in 1995 in “the glorious defense of the Bridge St Louis”.
Antenna of help
Each of the two bits (ends) of this antenna is a tube out of duralumin or brass of 1,5m length. One of the two bits (the vertical one here) is assembled on an axis which makes it possible to deploy it when the antenna left by the opening a block. The handle is consisted an assembly of extensions which one can add at will.
The nonlinear geometry of the two bits of this antenna of help makes the latter less powerful than the fixed normal antenna.
The antenna of help makes it possible to move the station (on condition that always remaining in the vicinity of outside) because it can be deployed through a crenel of bell GFM, a crenel of door, etc
Very short waves
Very Short waves (OTC). Why this choice? (by Lionel CIMA)
Many parameters influence the choice of the carrier frequency. They all do not go in the same direction and impose a compromise. One of the first factors to be taken into account is that of the power of the station. With their generators the works can provide for all the needs but certain casemates, isolated, do not have any important source of energy. They have only accumulators which one can hope to draw only about ten Watts. The antenna, of dimensioned sound, must be very short in order to offer less possible catch as well to the unfavourable shootings as with the friendly shootings of delousing. Of place in the blockhouses the obstruction of the station and for lack of its appendices must be reduced to its strict minimum. Lastly, by simple handling of the apparatus, a quickly trained personnel must be able to obtain an audible and stable signal.
In order to ensure the transmissions under good conditions the lack of power of the station pleads in favor of a low frequency carrier wave: 50kHz with 1,6MHz. But, with quality of equal reception, plus the frequency is small and more the antenna must be long! Tens of meters of antenna imposed here make the low frequencies prohibitory.
The geographical environment strongly conditions the choice of the carrying one. Indeed, the ground absorbs a certain quantity of energy of the emitted electromagnetic waves, and the phenomenon increases with the frequency, reducing of as much the range of the transmitter. For the range of waves ranging between 1.6 MHz and 30 MHz, one circumvents the problem of this - ground effect while emitting in the direction of the sky. The waves reflected on the ionospheric layers can be completely returned towards the ground without being attenuated. Also this method known as of indirect propagation can be used to cover a zone located at several thousands of kilometers of the point of emission. This solution, adapted to the fortification, could thus stage the disadvantages caused by the mountainous relief. However the indirect transmission enormously lengthens the distance between the transmitter and the receiver and is very dependant on the atmospheric and weather conditions making the connections unstable and hazardous.
By successive eliminations one comes to the solution of the high frequencies, retained by the service of the Military Transmissions, to ensure the radiophonic connections between the works of the Maginot Line. Stations OTCF (Very Short Waves of Fortress) are thus baptized because they use carrying at frequency located between 40MHz and 75MHz what, in other words, corresponds to wavelengths ranging between 4m and 7,5m (very short by report, for example, with the long waves of the frequencies lower than 1,6MHz).
Thus apparatuses OTCF need they only one antenna of to the more 4m length, compact to store and easy to change in the event of destruction. Moreover weather variations do not influence almost any more the waves of frequencies higher than 30 MHz, making the transmission rather stable. But the absence of reflection of this kind of waves on the ionospheric layers prohibited any indirect transmission. Also, with their low power of emission of 10W stations OTCF can be collected only with approximately 10km in flat ground and 25km in released tops. As much to say that their optimal use is done by direct visibility, when no natural obstacle interposes between the antennas. It is practically always the case between close works.
Handling of the station
Handling of station OTCF
If the station is connected to its food and its antenna and if it is granted on the frequency of emission of its correspondent, its handling is of a great simplicity. To put it in function it is enough to take down its microphone, suspended on the master switch. The emission is done then while pressing on the pushbutton of the microphone. The small oscillations of the needle of the milliammeter of frontage attest good performance of the lamp HF of emission.
When one ceases pressing on the button the station is put in reception mode. There, to obtain a quality of its optimal, some very light adjustments of the buttons - agreement and “super reaction” are likely to be made necessary by the environmental conditions (moisture, etc) and weather.
While not having any message to make pass, it can be convenient to maintain the contact or to allow the adjustment of the receiver of an occasional correspondent, inter alia that of a plane. With this intention there is the possibility of carrying out emissions prolonged without monopolizing the personnel of service. Indeed, in the center of the frontage of the station OTCF, a switch put in modulated position the lamp BF activates which oscillates and emits a continuous sound at fixed frequency.
Change of frequency
Change of frequency
In this case the complexity of handling results from the ultra simplicity of the station whose components are reduced to their strict minimum; there does not exist indeed any circuit of integrated adjustment. To differently grant the frequencies than to - sight of nose one must open the station, and make use of an additional wavemeter by coupling this last with the oscillatory circuit to regulate.
Wavemeter for the adjustment of station OTCF. During an exchange of documents, in 2004 our friend Aimé Salles (which we greet here) informed us of this rare lucky find. The wavemeter was in its case, out of leather, of origin.
Wavemeter. Photograph of official documentation.
This last, of 120mm length and 65mm of diameter, has selective oscillatory circuit which one can modify the frequency of agreement. A graduated drum makes it possible to read the selected wavelength directly. This kind of wavemeter uses the principle of absorption, i.e. it absorbs of energy only at the selected frequency. Its circuit is passive and thus does not require food.
Use of the wavemeter (Extracted the note of 1939)
The box-post office being stripped of its lid, to leave the coupling of the rather loose antenna, and to put the station on “Emission” while placing the switch “Phone Modulated” on “Modulated” or by blocking the push-button of the microphone, the switch being on the position - Phone.
To hold the wavemeter in the right hand, the whorl of coupling downwards. To introduce this whorl inside limps station, after having placed the drum graduated of the wavemeter on the position corresponding to the wavelength to obtain, and to couple it with the coil of emission of the Station. To then operate the variable capacitator of emission.
It will be noted that the agreement between the absorbing circuit calibrated wavemeter and the CO of emission of the station, appears by a maximum of current-plate with the milliammeter of the Station. Under these conditions, after having sought the minimum coupling between the coil of wavemeter and CO, to stop the variable capacitator of emission to the position which corresponds to this maximum. If the coupling of the antenna thereafter is improved there will be care to check the wavelength again.
How it is noted, handling is not close to everyone!
Circuits and components
Circuits and components of the OTCF
Above open station. Each compartment corresponds primarily to a circuit: emission on the right, reception on the left, low frequency and antenna in the center.
Station OTCF primarily consists of three circuits to a lamp each one:
- a circuit BF (for Low frequencies, or for voice frequencies) is used as amplifier of the audible signal. It is placed after the microphone during the emission or before the ear-phones at the time of the reception;
- two circuits HF (for High frequencies), carry out one the modulation and the other the demodulation on the carrying one.
A multiple relay, ordered by a pushbutton placed in the handle of the microphone, ensures micro commutation/ear-phones. By the same occasion this relay connects the circuit of antenna either on the modulator, or on the demodulator.
The 3 lamps of stations OTCF (one by circuit) are identical between them, which facilitates maintenance. They are vacuum tubes TMDT (three-electrode universal with low fuel consumption) whose general characteristics of the circuit of heating are the following ones: Ef=4V; If=70mA.
Diagram of the circuits
Diagram of the circuits
In frontage of the station the button - agreement varies the condenser C and the button - coupling operates the magnetic coupling between L and the antenna.
In frontage of the station the button - agreement varies the condenser C and the button - coupling operates the magnetic coupling between L and the antenna. The button “super reaction” varies resistance R.
The demodulator uses the principle of “super reaction” (or negative feedback). Thus the tension of plate of the lamp HF it is controlled by the signal modulating the carrying one. Information obtained is amplified by lamp BF before joining the ear-phones. The role of the variable resistor R is to improve quality of the sound. Its optimal value depends on the received power and is determined - with the ear.
Testimonies on Pierre Pointed (SFAM) collected by R.Cima
Photograph of the one of the two entries of the Outpost of Pierre Pointed. The entry is of face, framed by two huts of the external quartering, used in the absence of attack.
Pierre Pointue is one of the Outposts of the SFAM, face at the height of Castillon where in June 1940 the Italians pronounce their stronger attack. The OTCF played a big role, if not capital there.
June 22nd, 1940. 22:45.
It made black night [declares Sgt Leon Bosio] because the night had just fallen when these events occurred. [In addition Adj/Chef Lanteri writes that at 22:45, whereas all are at their station] the enemy emerges abruptly [-] I insert in the work all the personnel which I can touch. I am obliged to make evacuate the 2 rooms of shooting [whose embrasures are not tight and are the target of grenades] and I organize the defense of the entries. I put myself in connection by TSF with Cdt of the work of the PR of Castillon and I return account to him which the enemy occupies the tops of the work. I ask him for the support of the shootings of Artillery and to make even draw if possible on the work. These shootings are started a few moments afterwards.
The strong reaction of PR, alerted by OTCF, makes it possible to contain Italian until in the morning the men of the Outpost get clear, making even some prisoners.
Why Italian didn't neutralize the OTCF, by destroying its antenna for example?
At the time of their attack, [Lieutenant Médecin Dominique Leca explains me] Italian neutralized the telephone of the Outpost but did not destroy the antenna radio [-] which they confused with a pole for flag. Thus, as we saw, Pierre Pointue remained in communication with Castillon. But into the night [the Doctor adds] the radio station that we had inside the work, falls broken down! Indeed [the C/C Clément Michel specifies], the shells which we received made steal in glares our antenna and we remained isolated.
However, the next morning, after their exit of the shelter, the Alpine Jean Bellon restores the communications with PR and Adj/C Lanteri quotes it in these terms:
Charged with ensuring the connection by OTCF with the back, achieved its task with devotion, making the shot when its functions did not retain it near its apparatus.
And thus on June 23rd at 9:50 Adj. Malfroy (observatory of Garuche) can reassure the RSO of the Holy Agnes by this message:
By OTC Pierre Pointue states that it always holds.
Testimonies on Bridge St Louis (SFAM), collected by R Cima and Mr. Truttmann
This photograph of the crew of the Bridge St Louis was taken on June 25th, 1940 in the neighborhoods of their casemate which they defended until the end. Photograph Lucien ROBERT.
Pont St Louis is the Outposts of the SFAM located vis-a-vis the only road connecting Italy to Menton. During engagements Italian circumvents the Outpost which then finds private its communications [by couriers and telephone] backwards. Its only bond is then the OTCF.
The evening of the 22, at 18:45, notes Cape-Martin, whereas the deck-hands St Louis know that Italian is in Menton, therefore behind them, their radio operator break down cutting them definitively any information. The Alpine ones of rest lengthen on their straw mattresses without finding the sleep. To take to their turn of duty the men the bodies of their comrades span painfully. All are bearded and release a strong odor. The air is respirable only thanks to the forced ventilation actuated regularly by one of them. But the concern is elsewhere! They feverishly scan the visual space of their weak observation field.
What worried us then more [S/Lt Gros entrusts to us] it was the possibility of an attack by the sides and the tops of the work.
The events give them reason because they are then the target of several attacks. But each time they start to draw, the Cape-Martin, attentive with least their noises, supports them his fires.
The problem, involved in the breakdown of OTCF, is not that of information to be given but that of not received information. Indeed, on June 25th at 0:35 the armistice between into force and Bridge St Louis not knowing it continues its shootings, with the risk to cause an diplomatic incident or, more serious for him, a military strong reaction of Italian. In the summary of the operations of the Outpost one can read, concerning the June 25th:
6:05, without to have seen it arriving, an Italian soldier coming from Garavan advances towards the barrier. Two or three others are on the point of joining it. Gusts of FM disperse them. A green rocket is launched to ask for the artillery shootings [which for once do not come, and due!]. At 6:20, an officer and a group of some soldiers, also come from Garavan, again seek to approach the barrier. Guzzi, which is in FM, draws. A soldier seems to be killed and two or three others wounded. The others are withdrawn. At 8:25, the Bourgoin Sergeant, who observes with the glasses of the gun, announces two officers, the hands in the pockets, going down in the middle of the road. They are followed of a civilian (Mr. Acquaranne). Guzzi receives the order to draw in the air because the officers have neither arms nor coughs up and show themselves openly. The officers and the civilian fold up themselves and disappear behind the turning from the road. At 8:45, the Bourgoin Sergeant announces the appearance of a large white flag to the elbow of the road. Ringings of trumpets are made hear. Three or four minutes after two soldiers appear agitating the pole of this flag. A short moment and they descend the road in the direction of the bridge, followed by 150 soldiers approximately preceded by the trumpet continuing to sound. Intrigued (there is no shooting on this troop which follows the large white flag and seems to want to stop before the bridge), the Commander of the casemate then makes open the higher half of the door [of which bottom is wedged by the rubble which had with the bombardments].
Then having given order to the Bourgoin Sergeant to open fire with the least sign of its arm, S/Lt Gros advances towards the adversary and asks him that only one officer cross the bridge and approaches. Two or three officers advance. The dialog with a Colonel is about the following:
Our governments signed the armistice and the hostilities are finished since 1:35, at our hour; but you continue to draw, it is necessary to cease fire.
The answer of the Military cadet falls like a chopper:
I do not have any order to cease fire, I do not know the armistice and please withdraw itself with your men if not I will take again the shooting.
At this point in time the Bourgoin Sergeant arrives while saying:
My lieutenant, there are French officers who have just arrived.
Indeed, in one of its manuscripts (that its widow forwarded to me) the Captain Jean Blisson notes that it is Lieutenant Girardot, intelligence officer of the 58eDBAF, and itself which arrive at Pont St Louis bringing the written order of cease-fire. Lieutenant Malavielle and the Doctor-Lieutenant the Duke accompany them. For the crew it is the end of a nervous tension which did nothing but grow with the passing days.
The Italian officers, at once come to the front from the French, expressed their admiration for the defenders. [written the General Mountain. Then he adds:] They asked then the opening partial of the barrier to allow the passage of ambulances intended to evacuate the very many casualties of Chin.
This request is accepted in the condition that the Italian Command admits the changing, the evening even, of the garrison of the work by an equal manpower, out of weapons, and who would take again the mission. Lt-Colonel Moltoni, Chief of the E.M. of the Mondadori General, ordering the 5th Cosseria Division, having brought the agreement of his Chief, the changing of the station, having encircled since June 20th, is made at 6 p.m. by a new crew entrusted to S/Lt Etienne Piedfort. It is with pride that S/Lt Gros and its men, after having made a bit of toilet, leave their casemate then. Armed and in functioning order they are escorted by Italian to the line of demarcation from where they join the Cape Martin. They fulfilled their mission beyond any hope. Indeed, the Besson General inspecting the work in April 1938 would have said: this blockhouse will not hold 5 minutes!