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