Can an audio amplifier be used to transmit or receive radio signals?

[ofosot69]

Is it possible to make an audio amplifier transmit radio signals when connected to its output with a ferrite coil or any other loop antenna and make the signal receive with another audio amplifier?

I have this question in my mind because of these reasons:

1. An audio amplifier can respond to frequencies from 20 Hz to 20 kHz and when connected with a speaker, the coil in the speaker resonates as per the output frequency and if that can be connected to a loop antenna instead, it should radiate radio waves too.

2. While experimenting with a tape recorder many years ago, I encountered one strange thing. While I was adjusting the screw of the tape head, the screwdriver accidentally touched one of the head connectors that was connected with the audio amplifier. And I was able to hear an AM radio station. I guess the screwdriver was working like a whip antenna and the tape head was working like a loading coil.

So, based on these facts, I am assuming that a audio amplifier is able to transmit or receive radio frequencies without the need of any carrier wave. This would be done using direct induction just like how a matching transformer works between an audio amplifier and a speaker.

 

[mmckenna]

There are some guys that do this on —extremely— low frequencies. Like down in the tens of kilohertz range. I'll have to dig around and see if I can find the article on it. I believe they were using some sort of earth antenna, where the feedline was essentially connected to a deep ground rod.

 

[nd5y]

I heard that somebody used a PA amplifier connected to two ground rods, I don't know long or how far apart, and another person about 1/4 mile away was able to receive audio with some type of mic preamp connected to ground rods.

 

[jwt873]

There are audio frequencies, and radio frequencies. But there's no precise frequency that separates them.

I know of a a few stations that have transmitted in the 17 kHz range. NAA in Cutler Maine at (17.8 kHz) and SAQ in Grimeton. Sweden at (17.2 kHz). (SAQ is off the air and NAA is up at 24 kHz now running at 1.8 MegaWatts).

In the past, SAQ would occasionally fire up their transmitter for special events. You could connect an antenna to the input of a computer sound card and pick it up. There was Windows software available for this. (I tried but unfortunately I was never successful).

Edit.. Did a bit of digging after I posted this and found the windows software 'SAQrx' to use with a sound card. RX from 0 to 22 kHz. SM6LKM - SAQrx VLF Receiver