The only remaining working Alexanderson Alternator is transmitting again this Christmas Eve from SAQ Grimeton, Sweden (near Gothenburg city) on 17.2 KHz. (congratulations to Sweden for preserving and operating the Alexanderson Alternator).
I would like to receive and record this transmission here in Cardiff, Wales. The Alexanderson Alternator generates the 17.2 KHz carrier with a power level of 200 MegaWatt. At that frequency (in the audio spectrum) and at that power, propagation is likely to be global (subject to signal to noise constraints).
I'm building a simple receiver feeding into a preamp plugged into my Laptop PC that is running a sound recorder program. So far I have wound a 35 turn coil using many-stranded Litz wire onto a long ferrite rod and plan to resonate this at 17.2 KHz with a good quality capacitor. Then feed into a preamp built with a second tuned circuit. Simply then connect to the Laptop PC using 3.5mm Jack plug.
Can anyone advise me as to the best way to build this simple receiver? For instance will the ferrite rod be enough of an antenna or should I connect to a long wire? Will a preamp with effectively two tuned circuits likely provide enough gain? And so on....
During my reading I understand that a problem with VLF reception is signal to noise, there are several unavoidable noise sources such as global lightning storms.
Any kind of comment gratefully received.
I would like to receive and record this transmission here in Cardiff, Wales. The Alexanderson Alternator generates the 17.2 KHz carrier with a power level of 200 MegaWatt. At that frequency (in the audio spectrum) and at that power, propagation is likely to be global (subject to signal to noise constraints).
I'm building a simple receiver feeding into a preamp plugged into my Laptop PC that is running a sound recorder program. So far I have wound a 35 turn coil using many-stranded Litz wire onto a long ferrite rod and plan to resonate this at 17.2 KHz with a good quality capacitor. Then feed into a preamp built with a second tuned circuit. Simply then connect to the Laptop PC using 3.5mm Jack plug.
Can anyone advise me as to the best way to build this simple receiver? For instance will the ferrite rod be enough of an antenna or should I connect to a long wire? Will a preamp with effectively two tuned circuits likely provide enough gain? And so on....
During my reading I understand that a problem with VLF reception is signal to noise, there are several unavoidable noise sources such as global lightning storms.
Any kind of comment gratefully received.
Thanks, here is the quick link to the Alexanderson Association for convenience Alexanderson Association
Here is a YouTube link to a 4th July live transmission showing the machine in action 4th July Transmission
Of course the system was built in the USA by General Electric - a long time ago. In the description it is told that this system was possibly the only reliable way Sweden had to communicate with other countries during WWII - no wonder they preserved it.
Here is a YouTube link to a 4th July live transmission showing the machine in action 4th July Transmission
Of course the system was built in the USA by General Electric - a long time ago. In the description it is told that this system was possibly the only reliable way Sweden had to communicate with other countries during WWII - no wonder they preserved it.
Wow, that's interesting, nothing helpful, but questions. My hp 8591 goes down to 9kHz, if I put a very long wire into the 50 input do you think I would see anything.
Maybe I should run the experiment in the shed at end of garden on long extension lead with ferrites on.
Will look into more details of transmission when I get home.
Maybe I should run the experiment in the shed at end of garden on long extension lead with ferrites on.
Will look into more details of transmission when I get home.
There are several operating VLF transmitters globally running at different frequencies. The VLF band goes from 3KHz to 30KHz. There is also noise. I think you will see something on your spectrum analyser at 17.2 KHz. Shed at the bottom of the garden good idea.
Think you need at least one resonant circuit at 17.2 KHz.
Think you need at least one resonant circuit at 17.2 KHz.
@triplej Yes my typo 200KW thanks. No need for any diode the signal is morse code and carrier is on or off.
On the Laptop PC playing the sound file back at 1x speed the signal may not be audible but played back at a bit slower say 0.5x the carrier and the morse code should be audible.
Have not studied this in any detail but I understand this system was the way to communicate with ships and submarines in times gone by. VLF frequencies can reach into seawater especially if it is not too salty. There were (and still are) many VLF systems around the globe. The Alexanderson Alternator was soon replaced by very large thermionic valves/tubes.
During World War II International communications could not rely on Short Wave (easy to jam) or on subsea cables (easy to cut) so as I understand it VLF was often used.
On the Laptop PC playing the sound file back at 1x speed the signal may not be audible but played back at a bit slower say 0.5x the carrier and the morse code should be audible.
Have not studied this in any detail but I understand this system was the way to communicate with ships and submarines in times gone by. VLF frequencies can reach into seawater especially if it is not too salty. There were (and still are) many VLF systems around the globe. The Alexanderson Alternator was soon replaced by very large thermionic valves/tubes.
During World War II International communications could not rely on Short Wave (easy to jam) or on subsea cables (easy to cut) so as I understand it VLF was often used.
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I once worked at a LoranC station which has an Omega Receiver. It just used a vertical whip for 10khz.
There is a shaky Utube with a hacker using coiled wire on a big wooden frame
Here is a PCB antenna which has an SMD circuit .. https://www.elecbee.com/en-23616-Ul...-HF-Shortwave-Active-Receiving-Antenna-Module
Did you see the extensive wikipedia page.
good luck
There is a shaky Utube with a hacker using coiled wire on a big wooden frame
Here is a PCB antenna which has an SMD circuit .. https://www.elecbee.com/en-23616-Ul...-HF-Shortwave-Active-Receiving-Antenna-Module
Did you see the extensive wikipedia page.
good luck
The active WB loop antenna I recently designed, (clumsily) built and installed is my best antenna, yet. Although not designed for VLF, the following stations in the range of interest are visible in Panama near the border with Costa Rica. If I don't forget it I'll try to see if 17.2 KHz sig is visible. The "fat" sig at ~100k is from the power company.
@fubar3 That's very interesting so having worked in this field you understand the respect and admiration I have for same especially the Grimeton SAQ effort. Yes I read that SAQ is vertical signal so the vertical whip makes good sense as does a coil wound on a large wooden frame. Thanks also for the PCB link. I think that my ferrite core will concentrate the signal enough but will make an additional setup probably the vertical whip using a long wire. Thanks.
Yes I have had a good look on the internet but need to study more, thanks for reminding me.
Yes I have had a good look on the internet but need to study more, thanks for reminding me.
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@Aridace If you do see SAQ from Panama it's likely that they would welcome a report from you. Very impressed by your spectral representation! I'm guessing that a spectral peak will almost certainly show but another matter if you can read the morse code above noise.
Not sure about loop antenna for VLF, consensus so far seems to be "long wire preferably vertical" With a wavelength of around 17km it's pretty clear that no way to tune the antenna by it's geometry. Thanks.
Not sure about loop antenna for VLF, consensus so far seems to be "long wire preferably vertical" With a wavelength of around 17km it's pretty clear that no way to tune the antenna by it's geometry. Thanks.
@Kay Pirinha My first thought was to record the 17200 Hz carrier on my Laptop using the sound input then replay at half speed or less, then I would surely hear the carrier and the gaps made by the morse code, I might even be able to read some of the morse at a slow enough speed.
However to be realistic it would be better to hear the morse as it's transmitted in real time and your suggestion as regards a local oscillator is the way to achieve real time and 18000 Hz sounds like a good choice for the local oscillator. Logically this could be followed by a bandpass filter at 800 Hz to make the morse even clearer.
However to be realistic it would be better to hear the morse as it's transmitted in real time and your suggestion as regards a local oscillator is the way to achieve real time and 18000 Hz sounds like a good choice for the local oscillator. Logically this could be followed by a bandpass filter at 800 Hz to make the morse even clearer.
No, I can't read morse code, but I could record the audio. There are no other signals at the frequency. It's likely I can receive it because at night I could receive the German time signal at 77.5 KHz as well (power company messes it up, so still visible and audible during a nightly power cut).
BTW for VLF it's easy to build a receiver using cheap amps like the old quad mos series TL074. When using the grid for power supply, you need a balanced input on the ferrite antenna, then a ~ X100 amp. The 4th can be used as tunable ~sine wave18 KHz oscillator that feeds a single balanced mixer, suppressing only the oscillator. After the mixer a LPF at ~1KHz, also with opamps. The 800 Hz or lower, via amp to speakers. Because of the high interference it might be wise to add clipping diodes after the 17.2 amplification chain.
For 17.2 kHz it takes several 100 turns of wire to get best max rx signal