[rich.g.williams]

That’s very interesting. It would be great to see a working model especially of the Alexanderson Alternator.

[rich.g.williams]

Hi Jörg (and Fredrik),

I can see how the keying method would be called a “magnetic amplifier” because it uses the 3KWatt DC to control the 200KWatt SAQ carrier.

That said, if I understand correctly, its not a magnetic amplifier really. As I understand it the 3KWatt DC completely pushes the “output transformer” cores metal into saturation and the cores metal can no longer couple the Alternator output into the Antenna. This can happen to any inductor or transformer whenever there is a DC current component present in any winding.

I would guess that the 250 Volt 12 Amp max DC current is passed through a series resistor (that gets pretty hot) to limit the current to the 12 Amp maximum. So when the Morse Key is released the 250 Volt is applied across the resistor and an output transformer winding in series, the current flowing starts at 0 Amp and builds up very quickly to 12 Amp and the output transformer core is by then saturated. Similarly when the Morse Key is pressed the DC current flow is stopped (diverted and absorbed) and the magnetic core very quickly moves out of saturation.

A very similar principle is used by Fluxgate Compasses, in this case the Earth’s static field pushes the small core into varying partial saturation.

[rich.g.williams]

“two electrodes of 2m long buried underground, 100m apart and oriented 285°” That’s a good idea, does the ground need to be fairly dry for that to work? I’m assuming your electrodes are measuring the small potential difference created by the SAQ E-Field component. I have tried a 10m circular loop of insulated wire placed on the ground and it works well for some VLF transmitters but not SAQ (because SAQ M-Field is horizontal).

I will experiment with your setup next time SAQ transmits, I can easily get an electrode (Ground Rod) separation of 25m minimum.

[rich.g.williams]

“The integrating decoder currently works like this: It looks for dashes by integrating the signal multiplied by a dash-like folding function over a time interval that is slightly longer than one dash, thereby sensing the edges as well as the bulk of the dash. This procedure is repeated at a great number of points along the entire telegram, of the order every 10 ms”

That’s very interesting the “dash-like folding function” sounds like Fourier or convolution/deconvolution mathematics.

For the sake of interesting discussion there are many algorithms in pattern recognition etc that look for patterns (or images) regardless of exact dimensions. It could be possible using your approach to look for letters rather than individual dots/dashes. It could even be possible to look for words then you are soon getting into the realms of predictive text and using AI chips or software to do the job.

“However, my impression is that the ear and brain is unbeatable when the signal to noise ratio is poor” That’s interesting, That got me thinking about why? In part there is a lot of redundant information in a Morse code stream, people know what’s coming next and what makes sense. Ideally to test your software (or any future versions) a stream of random morse would be useful and then compare efficiency of your algorithm versus human Morse reader.

So one practical and probably useful idea that occurred is as follows:- Consider receiving the SAQ carrier window at 17200 Hz and also one or two nearby windows say windows at 17000 Hz and a window at 17400 Hz with say a 100Hz bandwidth. Now noise is broadband so you can expect the noise pulses to appear in all these three windows. Whereas the SAQ carrier will not appear in the other two windows. This gives a way to weight the validity of the SAQ Morse stream and then either to subtract the noise pulse, or to define an extra condition (Carrier, No carrier or Noise), or the noise information could be an input to your “folding function over a time interval” approach.

Well done interesting work!

[rich.g.williams]

This is very interesting, I have seen gerke-decoder mentioned on other forums and realise now that you wrote it back in 2020. Mathematically it very interesting with the integration approach. Have you experimented with cross-plotting interval times (on a test basis) to give a graphic representation? Do you assign a statistical probability to dots, dashes, spaces?

I only started receiving SAQ last year and when I did my first decode was reading the screen and using pen and paper to work out each letter. This last decode on Alexanderson day was faster, perhaps because I knew what was coming and could guess what words were after two or three letters.

As I understand it (and have read), that to turn on and turn off transmission of the 17.2 kHz carrier takes time so SAQ so as you mentioned previously “the intention was to send at 15 WPM then the early transmission was an amazing accomplishment” !!

In the old days (I’m talking about the 1960’s) Short wave radio was used extensively, Morse speeds could get quite high even over 15 WPM. I think 20 WPM was not uncommon.

I was really interested in amateur radio and wanted to get a licence but passing the RSGB Morse test was a problem for me. As a young teenager there was getting to the exam, there was how to practice. I felt that I would never learn to transmit and receive Morse at the 12 WPM needed for the exam – so regretfully I left it back then and got interested in sound systems and microprocessors instead.

[rich.g.williams]

“Would you dare driving an old-timer ralley with a modern Formula-1 racing car ? Certainly not !
Receiving an old-time transmitter with a soundcard and a PC or an SDR is as well improper style or even bad taste, but in no way a remarkable achievement.
Everybody can do so !”

This is a very unfair comment I say this for the following reasons:

– The original Kungsbacka Receiver Station, it is noted that the Receiver antenna “consisted of two copper wires set up on 9 m tall telephone poles along a stretch of about 13.4 km, over Kungsbackaån and southeast out through Hanhals and Fjärås parishes to Skärsjön on the south side of Lygnern” So how many of us have access to such a 13.4 km length antenna.

– I want to receive SAQ transmission in Cardiff Wales UK and my garden allows for a 25 metre wire antenna so must use “every trick in the book” to receive SAQ with certainty at good signal strength.
– To build a simple tuned receiver modern electronics is easiest and to avoid need for hardware BFO etc its easy to record the 17200 Hz carrier directly using a Laptop PC (at 48 k samples/sec) and use software to detect the Morse code.

My belief is that the SAQ transmission propagates around the globe so for people trying to receive in the opposite hemisphere use of modern electronics and software processing is essential.

Also to be perfectly honest I have looked at some of the old receiver designs and to me they look very bloated, over complicated, difficult to understand and difficult to build – they do not follow the most important designers commandment which is “keep it simple”

I agree that existing receivers built originally should be looked after and kept safe but I do not agree that people should be encouraged to rebuild those old designs in the 21st Century.

[rich.g.williams]

I found this description of Kungsbacka Receiver Station https://www.radiomuseet.se/medlem/audionen2/nr4_2005/kung.html

also noted that the Receiver antenna “consisted of two copper wires set up on 9 m tall telephone poles along a stretch of about 13.4 km, over Kungsbackaån and southeast out through Hanhals and Fjärås parishes to Skärsjön on the south side of Lygnern”

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