1-20Hz receiver solution needed

[neazoi]

Hello,
The frequencies below 20Hz are not audible to the human ear, as well as the frequencies above about 20KHz.

For frequencies above 20KHZ we use RF mixers to down convert the portion of spectrum to the audible range.

Can the same principle apply on frequencies below 20Hz?
How can I up-convert the 1-20Hz spectrum, to higher audible frequencies, what mixer should I use? (there are no commercial mixers for such low frequencies I guess)

 

[enjunear]

Hello,
The frequencies below 20Hz are not audible to the human ear, as well as the frequencies above about 20KHz.

For frequencies above 20KHZ we use RF mixers to down convert the portion of spectrum to the audible range.

Can the same principle apply on frequencies below 20Hz?
How can I up-convert the 1-20Hz spectrum, to higher audible frequencies, what mixer should I use? (there are no commercial mixers for such low frequencies I guess)

With any modulated carrier, the modulation (information) on the carrier must be at a frequency less than the carrier. E.g. 2 kHz AM voice on a 2 MHz HF carrier. You can down-mix the 2 MHz carrier with another 2 MHz tone, and get out the baseband audio signal. The same ratio must hold true in the 1-20 Hz situation. If you have information encoded on a 20 Hz carrier, then the modulation frequency (signal bandwidth), must be something far less than 20 Hz... as in sub deci-Hertz, which will take forever to transmit data of any kind.

Or are you simply trying to mix a single tone in the 1-20 Hz range, up to something in the audio region? In that case, you could mix your signal with 1 kHz, and get an output from 1001 - 1020 Hz. I would imagine the same transistor-based mixer could be tweaked to work at audio frequencies w/o too much trouble.

 

[kak111]

You must have an oscillator for audible range and use
that 1...20Hz as FM-modulation signal for audible oscillator.

This case use VCO (voltage controlled oscillator as FM-modulator)
This is normal case used in synthesizers as musical instrument.

ie. you have oscillator 400Hz and after modulation 400...420Hz

or construct the molulation so that FM gives change of audible oscillator
bigger than 1...20Hz. ( 800...1200Hz "syncronized" with 1...20Hz)

Regards KAK

 

[neazoi]

Ok as far as I can understand I use the same principle that a simple transistor mixer uses for up-conversion.
Up-conversion, has been used in some transverters like this one https://www.radiocom.net/txvr.jpg to convert 0-500KHz range to 10-10.5MHz using the sa602 chip, but I do not know how low on frequency can actually this chip be used.

 

[chuckey]

I would go for Kak111 idea but it suffers from the relatively low change of pitch on its output(402 - 420). If you multiplied this , say by X8, so the output frequency range was 3216 - 3360, then mix it down again say with a 3000 oscillator then the output frequencies would be 216 - 360, which might be better.
Another way would be to look at the period of the wave form (.5 - .05 S), use this to generate a DC roughly proportional to the pulses duration and use this to directly frequency modulate a audio oscillator running at a convenient frequency. By adjusting the frequency V voltage characteristic of the oscillator you could get a tremendous swing 200 HZ - 15 KHz ?
Frank

 

[neazoi]

The purpose is to bring these infrasounds to the audible range for further study.
Let me make myself more clear.
These frequencies are meant to be picked up by a kind of antenna and cannot be used to modulate a vco, even when amplified their level will be too low.

It is exactly the same principle like these "natural radio receivers", which are basically high gain audio amplifiers, connected to an antenna wire.

But in my case receiving frequencies below 20Hz means you have to up-convert them to more than 20Hz in order to be able to listen to them.

I am trying to find a way to be able to listen to the Schumann resonances

 

[kak111]

As i wrote.............
Construct the modulation so that FM gives change of audible oscillator
bigger than 1...20Hz.

It means

With setting the modulation signal level to VCO you can set
the range of output frequency as needed.

Regards KAK

 

[neazoi]

As i wrote.............
Construct the modulation so that FM gives change of audible oscillator
bigger than 1...20Hz.

It means

With setting the modulation signal level to VCO you can set
the range of output frequency as needed.

Regards KAK

RF signals of this kind are both FM and AM. In fact they are more AM. how will the fm modulation cope with this? except if I miss something here