Transistor to Amplify Radio Signals Sub-100Hz - Page 1
Forum section: electronics / rf-microwave

author: Geschwessaut
author_rank: Newbie
timestamp: December 09, 2020, 04:28:34 am
content: Hey guys,Completely new to radio receiver circuits so forgive me for my lack of understanding on the matter. I was trying to pick up radio signals from 0-100Hz. I connected an antenna to a Low-Pass Filter which the output of the Low-Pass Filter was then connected to the analog pin on my 16-bit resolution ADC which was hooked up to my Arduino and, as I was anticipating I got 0 readings. I did a little bit of problem solving and finally stumbled upon the solution to use a transistor to amplify the signal and make it readable to my ADC. I have 2n2222 transistors, however I am new to transistor amplification circuits and don't know what transistor I would need to amplify signals received by my antenna on the breadboard. Could anybody give me an idea of what transistor I would use for this, or if this is even possible sub 100Hz?

author: radiolistener
author_rank: Super Contributor
timestamp: December 09, 2020, 04:45:08 am
content: Quote from: Geschwessaut on December 09, 2020, 04:28:34 amFor so low frequencies, I think it's better to use bandpass filter with high Q resonant circuit in order to remove unwanted noises.Something like low loss inductor and low loss vacuum capacitor with low resistance conductors (silver plated copper wires, etc).It will accumulate AC energy between antenna and LC circuit at resonant frequency and will works as a noise free amplifier.I think with good 24 bit sound card you will not need amplifier, because sound card sensitivity is good enough to see atmospheric noise floor.For example, you can listen submarine communications on 18-22 kHz with a cheap integrated 16 bit sound card with no problem. Just put a long wire on the sound card line-in, with no filter and no amplifier. With a high Q resonance circuit it will be even better.The main issue with so low frequency is antenna size. You will need a very long antenna size to get enough efficiency in order to get low signals above noise floor.Also you can use left and right channels of sound card with two perpendicular antennas in order to receive signals from specific direction. It allows to reduce noise which come from the noise-source at unwanted direction.

author: Geschwessaut
author_rank: Newbie
timestamp: December 10, 2020, 05:29:27 am
content: Quote from: radiolistener on December 09, 2020, 04:45:08 amNonetheless, it will still not allow my ADC to pickup sub millivolt reading from the high q resonant circuit, in which case a transistor would be able to amplify the tiny amounts of electrical energy a radio wave carries, right? After the radio wave has been amplified by the transistor, then I can read it with an Analog to Digital Converter?

author: Leo Bodnar
author_rank: Frequent Contributor
timestamp: December 10, 2020, 09:46:33 am
content: Have a look at ELF receivers, there are a lot of good tested and tried projects in there.E.g.http://www.vlf.it/is a good startELF amplifier design mostly depends on your antenna - in simple terms, are you picking up magnetic field or electric field.Leo

author: Geschwessaut
author_rank: Newbie
timestamp: December 10, 2020, 02:53:07 pm
content: Electromagnetic, I.E. Radio Waves!

author: petert
author_rank: Regular Contributor
timestamp: December 10, 2020, 03:06:10 pm
content: Quote from: Geschwessaut on December 10, 2020, 02:53:07 pmYou can have antennas that pick up the electric field, such as a dipole antennas, and those that pick up the magnetic field, such as those made for AM radios, a coil wound around a ferromagnetic core.

author: Leo Bodnar
author_rank: Frequent Contributor
timestamp: December 10, 2020, 04:57:32 pm
content: Perhaps "antenna" is a bad term to use for signals below 100Hz, unless you talk about Sanguine or Zevs transmitters.You'd expect "antenna" thing to be roughly comparable to the wavelength of the carrier.100Hz carrier has the wavelength of 3000km.You are, basically, sensing slowly changing electric or magnetic field usingsensor, probeorpickup.Approach it as if you were measuring DC field strength and decide which one you want to go for.Electric field is much easier. I have never seen Zevs on magnetometer charts if you are after that one.Leo