- Detta ämne har 4 svar, 1 deltagare, och uppdaterades senast för 2 månader sedan av Jörg Hofstetter.
12 oktober, 2015 kl. 12:56 #3374
Brian / G3GVB (moved from comments)
Is the SAQ transmission pure CW or is it MCW , ?
Is the carrier modulated with a sound tone automatically by the generator. ? My ex-Royal Navy RX (Murphy B41) works best on SAQ transmissions with the BFO off!. Hence my question .
73, Brian, G3GVB and AC4UA
3 oktober, 2023 kl. 19:36 #10293Jörg HofstetterGäst
thank you very much for the detailed explanation of the Morse transmission in Grimeton.
I will now make a diagram or two about it and explain the principle with some text as simple as possible. If it’s ok for you, I’ll send you a draft, for a review (by email? my email ist: email@example.com).
After that I will try to put this text in the German Wiki (https://de.wikipedia.org/wiki/L%C3%A4ngstwellensender_Grimeton). We you are interested, we can discuss how to proceed with the English wiki (since I am not English speaking, I need some support).
Idea: A colleague of mine was visiting Grimeton. It was difficult for him to follow the English explanations. Why not put up a QR code on the wiki entries of different languages on a wall? (There is free software for QR codes, I could help).
23 september, 2023 kl. 11:47 #10287Jörg HofstetterGäst
On October 19, 2015 AlexanderSAQ said in the forum:: “We have no modulator”.
I assume this means: you are not using a “magnetic amplifier” for modulation.
But how do you generate the outgoing “square wave” signal with the Morse information?
I suspect that it is not possible to simply turn the transmitter on and off. Sometimes mechanical changes were made to the antenna to reduce the transmit power.
On Wikpedia https://en.m.wikipedia.org/wiki/Grimeton_Radio_Station I found a text which is not quite clear to me:
“The switching on and off of the transmitter with the signalling morse key makes the driver motor change frequency just a bit, so the frequency is outside the narrow band of the antenna and thus transmitted with much less power. In fact this forms an early and clever form of frequency shift keying (FSK)”
It sounds like this to me: You control/shift the frequency of the driver motor to change the frequency. How is this done?
Is this Wikipedia entry really correct?
1 oktober, 2023 kl. 12:22 #10289
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
19 oktober, 2015 kl. 18:02 #3428
The simple answer to your question is that we have no modulator, it is pure CW we are sending out. There is however no prefect square wave but it has a short rise- and decay time (about 12 ms).
However, Arne Siko here at the Alexander association had a data simulation made on a rough theoretical model of the antenna, and in the curves of that simulation one can discern an overlay that would be perceived as a 1100 Hz tone. We have never thought of this, as we see an overshoot in the amplitude at approximately 15 ms, that we thought little of, but not found any explanation. All this can be seen on the attached report.
/Fredrik Wiklund @AlexanderSAQ with help from Ola Hernvall