I'm about 1100Km away from SAQ (mostly over ocean) so hoping the signal will be strong enough here.
Thanks for your advice @bucks bunny @Aridace @MarcelvdG
Thanks for your advice @bucks bunny @Aridace @MarcelvdG
Quick test running first with test generator at 17200 Hz and then without test generator, the test generator peak is about 40dB stronger than others, what are these other peaks ? Are they VLF transmitters or local interference?
Most of the wide spectrum noise is picked up when I connect antenna wire and earth wire.
The frequencies of the other peaks are 16.42 KHz 18.22 KHz 19.56 KHz 20.27 KHz 21.68 KHz and 21.99 KHz.
Most of the wide spectrum noise is picked up when I connect antenna wire and earth wire.
The frequencies of the other peaks are 16.42 KHz 18.22 KHz 19.56 KHz 20.27 KHz 21.68 KHz and 21.99 KHz.
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Correlate the peaks with this list: https://sidstation.loudet.org/stations-list-en.xhtml
Peaks showing up on the ferrite alone could be nulled and if so, one side of the ferrite axis points in the direction of the station.
Peaks showing up on the ferrite alone could be nulled and if so, one side of the ferrite axis points in the direction of the station.
The peaks correlate with UK, France, Norway, India, Italy. I will try without antenna wire and earth wire and move the ferrite around. Looks like I am picking up VLF stations so should be able to see a peak when SAQ transmits.
Yes a low pass filter in software, yes can be applied, just getting the peaks at the moment. The live run will be recorded to disk and processed after. Can be filtered (low pass, bandpass and high pass) and also replayed at half or quarter speed to make the 17200 Hz SAQ audible.
Keep in mind that the amplitude scale is logarithmic so even though the low frequency noise looks bad there is about 45 dB between noise and the strongest VLF peak.
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Yes I have done some tests and moving the ferrite does select peaks when no antenna or earth connected. However the signal is many dB stronger with Antenna and Earth connected.
See examples first Ferrite Rod no Antenna no Earth the with Antenna and Earth.
It seems there are no peaks very close to SAQ frequency. The peaking that shows at 17200 Hz is the resonance of the Ferrite Rod so hopefully the SAQ pulse will be quite strong.
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Apparently you're lucky to be living in a region with a low level of EMI, reminding of my stay in Belgium, over 30 years ago. IOW a region where a mini-whip would be enough from a few KHz up to ~7 MHz.
Yes seems that the EMI is low, that said I was thinking about turning the mains power to the house off during the recording.
I'm wondering if SAQ frequency will beat with the other VLF frequencies and render the morse audible even replaying at x1?
I'm wondering if SAQ frequency will beat with the other VLF frequencies and render the morse audible even replaying at x1?
Remember that the other stations are FSK with bitrate up to 200 bps. Beating with them won't sound well. So saving to disk and then applying a BFP to eliminate adjacent FSK makes sense. If needed, Micro-cap has the option to use a wav file as an input, and after processing (for instance mixer) the output is in the audible range but I never tried it out. What also works and might be simpler is undersampling, like I showed in the hardware example.
Yes I can hear the other stations, slowing replay down to about 0.1 and it starts to sound a bit like Morse code, sounds like same thing being repeated over and over. I am amazed that such a simple construction seems to be picking up VLF stations !
With replay at 0.1, bitrate decreases proportionally. resembling the sound of morse code. ELF and VLF are mostly audio, some people are hooked to the amazing sounds they can hear and even developed comb filters to eliminate grid harmonics.
Your location probably is ideal, so the present experience could be used.
https://en.wikipedia.org/wiki/Whistler_(radio)
https://en.wikipedia.org/wiki/Whistler_(radio)
That will only happen when there is something non-linear enough to produce the beat product; maybe if the signals are strong enough to drive your LM358 into and out of its dead zone.
It looks like you were right about the amplifier noise being sufficiently low. Even without extra aerial, the spectral peak at 17.2 kHz is well above the noise floor. The distance to the surrounding peaks remains about constant with and without the extra aerial, so it must really be received atmospheric noise rather than thermal or amplifier current noise.
Upon reflection I would prefer to use a better OpAmp. The 300K input resistor and the OpAmp I used contribute to noise. A better JFET type OpAmp as a non inverting amp with low gain would feel better. It would also be better to have more analogue bandpass filtering. The antenna I have is not big enough (high enough) really to do a good job.
TI do slate the LM358 now, probably because they have released an upgraded part, they have published a really detailed critique of the LM358! I often use the Analog Devices AD820, its a good general purpose FET amp with good noise figure and open loop gain of 40dB at 20 KHz.
Its hard to say what noise is coming from where at the moment,
Have recorded and processed the full Grimeton SAQ Christmas Message 24th December 2023 as recorded in Cardiff, Wales, UK.
It is attached as a ZIP file containing the processed wav file.
How have others got on?
CC @SAQ Grimeton
It is attached as a ZIP file containing the processed wav file.
How have others got on?
CC @SAQ Grimeton
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