@bucks bunny Yes I wanted more turns but don't have Litz wire long enough. In the past I have seen Litz wire used to wind Long Wave coils on ferrite cores.
Do you think it will work if I wind a coil hundreds of turns long with single stranded enamelled Copper wire. Thanks for your advice.
Do you think it will work if I wind a coil hundreds of turns long with single stranded enamelled Copper wire. Thanks for your advice.
It looks like very few turns: some 1,000 would be better as the induced voltage is proportional to the number of turns. Q factor doesn't matter much. The easy way is to mount the rod in a drill and wind up as much (thin) wire as possible. Measure inductance, add the required C for resonance. This makes sense because SAQ no longer runs as maximum power: it has been reduced to 80 KW.
https://alexander.n.se/en/the-radio-station-saq-grimeton/the-alexanderson-transmitter/
@Aridace Thanks for sketching out a design method. The TL074 seems a very good choice as its input current specs are in picoAmps and I have some of them.
I cannot read Morse code but I can read Morse code if I record the sound as I mentioned previously "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"
You got me thinking now that I can replay the sound file at even slower than 0.5x and decode each Morse symbol by looking each symbol up from the Morse table. That way I can rewind over each symbol to confirm. Tedious but can be done.
I cannot read Morse code but I can read Morse code if I record the sound as I mentioned previously "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"
You got me thinking now that I can replay the sound file at even slower than 0.5x and decode each Morse symbol by looking each symbol up from the Morse table. That way I can rewind over each symbol to confirm. Tedious but can be done.
@Aridace Yes 1000 turns but will it work without Litz wire I don't have Litz wire.
How is it that Q does not matter much? I thought that high Q will boost the Voltage massively at the resonant frequency?
Will it not be a trade off between voltage increasing proportional to square of number of turns and Q degrading as the resistance of the very thin wire starts to become large.
I'm thinking that the skin effect at such low frequency will increase wire resistance (to that low frequency) and therefore another factor degrading Q.
The distance from Grimeton SAQ to where I live is only 1,190 km so the reduction from 250 KW to 80 KW should not make much difference here in Cardiff, Wales.
How is it that Q does not matter much? I thought that high Q will boost the Voltage massively at the resonant frequency?
Will it not be a trade off between voltage increasing proportional to square of number of turns and Q degrading as the resistance of the very thin wire starts to become large.
I'm thinking that the skin effect at such low frequency will increase wire resistance (to that low frequency) and therefore another factor degrading Q.
The distance from Grimeton SAQ to where I live is only 1,190 km so the reduction from 250 KW to 80 KW should not make much difference here in Cardiff, Wales.
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No need for Litz wire - the very last thing one needs is a Q-factor of 1,000 at 17.2 k. 10 would be enough already, as otherwise noise pulses are lengthened too much, messing up the signal. Few know that the same S/N as obtained by tuning can be obtained from a (carefully designed) wideband loop. From that perspective, 0.1 mm dia enameled Cu wire would do the job but is rather fragile to handle. Hence more turns improves performance more than higher Q-factor. Simpler than a mixer is a S/H, would produce the difference frequency when sampling 17.2 KHz with ~18 KHz.
@Aridace OK I will wind a 400 turn thin wire coil on my ferrite core. If the Q at 17200 Hz is too high I will add series resistance. The ferrite core is 200mm by 12mm so it will concentrate the inductance. I also plan to have a vertical wire to connect. I have no idea if the ferrite antenna will be directional but I will align its axis with Grimeton SAQ.
With thin wire, wild wound (not each turn on the rod next the following one) the Q will be OK. Ferrite antennas are very directional but that only regards the position to null out interference. So that's more important than aiming at maximum signal, which is perpendicular to the axis (draw the magnetic field lines from a vertical antenna, and how they have to enter the rod for maximum induced voltage).
How about decoding the stream with an Arduino general-purpose MCU. Just poll the signal with a GPIO pin and catch the changes in state. There needs to be some logic to ignore noise.
That's an interesting idea!
Now you mention processing it would also be possible to process the recorded sound file using something like Visual Basic or Visual C++
Whichever way its processed, because the Morse is keyed in real time by an expert radio operator (rather than a machine) the program would need to be smart enough to adapt to the timing.
Another way would be to find an SDR program that had a built in function that decoded Morse code.
Paraphrasing for this application from Wikipedia "A basic Software Defined Radio (SDR) system typically consists of a personal computer equipped with a sound card, or other analog-to-digital converter, preceded by the VLF front end. Signal processing is handed over to the general-purpose processor, rather than being done in special-purpose hardware. Such a design produces a radio which can receive different radio protocols (sometimes referred to as waveforms) based solely on the program used"
Now you mention processing it would also be possible to process the recorded sound file using something like Visual Basic or Visual C++
Whichever way its processed, because the Morse is keyed in real time by an expert radio operator (rather than a machine) the program would need to be smart enough to adapt to the timing.
Another way would be to find an SDR program that had a built in function that decoded Morse code.
Paraphrasing for this application from Wikipedia "A basic Software Defined Radio (SDR) system typically consists of a personal computer equipped with a sound card, or other analog-to-digital converter, preceded by the VLF front end. Signal processing is handed over to the general-purpose processor, rather than being done in special-purpose hardware. Such a design produces a radio which can receive different radio protocols (sometimes referred to as waveforms) based solely on the program used"
As Xmas eve happens in a few days and SAQ receivers have to be constructed and tested, this circuit diagram with sim might speed up the process. X1,2,3 are a difference amplifier.The BC550 and connected components (including X5) work as sample-hold, with the CD4093 functioning as sampling frequency generator. X6, simple LPF (~1KHz) and X9, settable amp with clipping diodes to protect connected amps and ears.The sim shows that just ~84 µV (pp) across L1 provides ~70 mV (pp) of audio over R20.
Clear also that the S/H is far from perfect, just good enough, as are the opamps, as shown in the plot of V(11). With ~840 µV at the setting in the circuit, X9 is clipping already. Below clipping, the FFT of the output shows THD is good enough as well. Testing is possible by tuning L1C3 to 60 KHz and setting the sample frequency to 19.67 KHz. This should provide reception of the 24/7 timing signals.
Clear also that the S/H is far from perfect, just good enough, as are the opamps, as shown in the plot of V(11). With ~840 µV at the setting in the circuit, X9 is clipping already. Below clipping, the FFT of the output shows THD is good enough as well. Testing is possible by tuning L1C3 to 60 KHz and setting the sample frequency to 19.67 KHz. This should provide reception of the 24/7 timing signals.
@bucks bunny Yes 300 turns. So far my resonant ferrite rod is about 38 turns with about 580nF capacitor. I have some really stable 8n2 COG capacitors so after a quick calculation one of the 8n2 capacitors should resonate with about 300 turns. So I think I will wind over three hundred turns and then remove turns until it resonates at 17200 Hz (plus or minus one or two turns).
I also found a good 0.68mH rod inductor that should resonate with about 125nF capacitor.
I also found a good 0.68mH rod inductor that should resonate with about 125nF capacitor.
@Aridace Waw that's very impressive!!
I agree completely with your front end design. As I understand it R7, L2 and V6 is a separate test circuit so that you can induce a 17200 Hz test carrier from a distance away into the ferrite without loading it. The 8n5 capacitor is a perfect choice for me because I already have very good 8n2 COG capacitors, after a quick calculation one of the 8n2 capacitors should resonate with about 300 turns on my ferrite rod.
So your circuit is putting 50K resistance across the tuned front end and will define the Q achieved. I'm thinking that I will construct the front end exactly as you show using X1, X2 and X3 from the TL074 but then add the fourth opamp part X4 on as a variable gain amp feeding directly into my Laptop PC sound input. This will make construction easier for me.
That said, if there are others with enough time I think they should construct your complete circuit as shown. I really like the front end as you designed it!
I think the TL074 is fine for this application.
I agree completely with your front end design. As I understand it R7, L2 and V6 is a separate test circuit so that you can induce a 17200 Hz test carrier from a distance away into the ferrite without loading it. The 8n5 capacitor is a perfect choice for me because I already have very good 8n2 COG capacitors, after a quick calculation one of the 8n2 capacitors should resonate with about 300 turns on my ferrite rod.
So your circuit is putting 50K resistance across the tuned front end and will define the Q achieved. I'm thinking that I will construct the front end exactly as you show using X1, X2 and X3 from the TL074 but then add the fourth opamp part X4 on as a variable gain amp feeding directly into my Laptop PC sound input. This will make construction easier for me.
That said, if there are others with enough time I think they should construct your complete circuit as shown. I really like the front end as you designed it!
I think the TL074 is fine for this application.
R1,2 are in series so the load in the sim is 200k (neglecting the influence of the TL074). My experience in connecting receivers to a computer is very negative, living in a region with field strength of "most popular material" at least 20 dB below that in Europe or urban USA. Much work to prevent interference from the computer and connected equipment. So for simple and single purpose, in my case a dedicated RX is best.
When feeding the signal to an audio input of the PC, a kind of clipper might be useful to prevent overload, as the TL074 at +/-5V will deliver ~8V(pp).
When feeding the signal to an audio input of the PC, a kind of clipper might be useful to prevent overload, as the TL074 at +/-5V will deliver ~8V(pp).
