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Dear Jens,
The secondary windings of the two transformers in the high frequency amplifier system are directly connected to the antenna. The voltage generated across the secondary windings is 2000 V, so here are high requirements for voltage strength of the insulation.
In addition, the secondary windings must withstand lightning strikes coming in from the antenna.As protection for the secondary windings, they are connected to an over-voltage protection, a so-called Jacob’s ladder.
In the event of an over-voltage, an flash-over occurs on the protection and the arc is then led up into the “horns”, where it goes out.
Lightning strikes have thus not been an obstacle to run the transmitter.//Fredrik
Bill;
The Alexanderson alternator was in fact designed to transmit both morse code and speech, however the unit at World Heritage Grimeton Radio Station in Sweden is able to send morse code only, this due to the antenna design. The energy in the antenna at resonance is much higher than the input from the transmitter. That means that there is a rise and decay time of some ten milliseconds on the antenna when keying down. This limitation in the antenna will allow only morse code to be sent.
The Grimeton site did not have any means to receive the return signal from the transmission site at Rocky Point on Long Island, US. Instead a dedicated receiving station was located in the city of Kungsbacka, located some 50km north of Grimeton. This arrangement with two separate sites was made in order not to take any risks that the transmission should disturb the reception.Fredrik / Alexander association
Bob;
Thanks for your question about the 3-phase motors.
The 2-phase system was initially the most common power system in Schenectady NY, USA where Ernst FW Alexanderson worked and developed his alternator. When the 3-phase system later was taking over, General Electric and Alexanderson could not financially justify the redesign of the very complex speed control system from 2-phase to 3-phase and therefore kept it 2-phase for the main drive motor. However to change all the small drive motors for water cooling, rheostat circulation an so on, from 2-phase to 3-phase was an easy task.
In the late 1890´s the Westinghouse engineer Charles Scott developed a three-phase transformer that allowed for easy conversion of 2-phase to 3-phase or the reverse.
At Grimeton radio station we have a large 50kV – 2.3kV Scott-connected transformer in the external transformer building, which is supplying the drive motor with its 2-phase power. Inside the transmitter building there is a much smaller 2.3kV – 440V Scott connected transformer which will convert the 2-phase back to 3-phase for supply to all the small motors in the system.Fredrik / Alexander association
Many thanks for your feedback on the today’s SAQ test transmission!
Today was very special, as the transmitter has not been in operation for a few months, due to extended building maintenance.
Additionally, during this period, we have made major service on the compensation liquid rheostat, cleaning it out and filling with new fresh water.There are two large liquid rheostats, filled with water and sodium carbonate, where the resistance can be adjusted by increasing or lowering the water level using a motor operated gate. The rotor of the main drive motor is wound three phase, and each lead goes to the start liquid rheostat, to three separate copper bars, from which a set of hollow tubes, with different lengths are mounted, hanging down towards the water level. When operating the gate from the control panel, the water level increases, more tubes will come into contact with the water, and the resistance between the three rotor phases will decrease, giving the motor more torque. At key down, a second compensation liquid rheostat is connected in parallel with the first, resulting in a lower resistance, giving the drive motor a good “torque boost” in order not to drop in speed when all the power shall go out to the antenna.
As the compensation rheostat only is connected when the morse key is pressed down and as the actual load only can be determined when the alternator is connected to the antenna, we have been unable to refill the compensation rheostat with sodium carbonate until today. We use food grade sodium carbonate, with very low chloride levels.
After some calculations, we filled 250g into the rheostat and started the alternator. We managed to get a good tuning of the drive motor speed but the compensation rheostat was at its upper max position, indicating that the sodium carbonate concentration was too low.
So, we added another 50g, retuned the drive motor, added yet another 50g and made a final tuning of the drive motor.
That was what you were hearing during those long tuning sessions today.
After that we ran our “VVV VVV VVV de SAQ” message a couple of times to check that we got good speed stability and good power to the antenna.So, things look good for tomorrow’s transmission which we very much look forward to.
Fredrik / Alexander association
Dear Jörg,
Here’s a simplified description of how the morse code is created when transmitting with SAQ:
The Alexanderson alternator is supplying a magnetic flux with the frequency 17,200 Hz, or 17.2 kHz via 64 separate windings, each delivering 100V and 30A, which is led to two separate transformers in the high frequency amplifier. 32 leads are going to the first transformer and another 32 leads are going to the second transformer.
Each transformer then has 32 individual primary windings, each of them electrically insulated from each other.
2000V is generated in the secondary winding of each transformer. The secondary windings from both transformers are connected in parallel and further connected to the antenna.
However, there is also a third winding in each transformer, located between the primary and secondary winding. This winding can be supplied with 250V DC, 12A current (3kW), controlled by the morse key. When the morse key is up (no signal) the DC current is flowing through the third middle winding, reducing the amount of energy being induced from the primary to the secondary winding.
At key-down, the current in the middle winding is blocked, and full power is induced into the secondary winding.
So, at key-up there will be a very limited amount of energy going out into the antenna. The magnetic amplifier is simply “leaking” a little carrier wave, which can be detected if you have a sensitive receiver.In addition to the two transformers, there is a second system, also operated by the morse key, to alter the antenna resonance frequency.
In the lower part of the “magnetic amplifier” two “transductors” are located. A transductor is a variable inductance, consisting of a primary winding for the AC and a secondary winding for DC, both placed around an iron core. The iron core works as an inductance for the AC winding, however when 250V 30A current is flowing in the DC winding, the iron core is magnetically saturated and thus reduces its inductance.
The antenna is a resonant circuit with its resonance frequency set to 17.2kHz and the two transductors are connected inline with the antenna.
This means that by key-up, the antenna is not tuned to the resonance frequency, due to the changed inductance in the two transductors.
At key-down, the 250V 12A DC current is blocked, the inductance will be altered and the antenna will be in tune.Ernst Alexanderson invented this system, with all its components, to allow a relatively small DC current of 3kW to control a very large power of 200kW.
Wikipedia is not reflecting the correct function and should be updated.
The speed of the drive motor is very constant. The speed control system is very sophisticated and can be explained in a separate reply, if required.
I hope this explanation will give you a basic understandning of how the morse code is created.Fredrik / Alexander association
