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.

 

[crutschow]

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.

No, your are not understanding the "facts".
You need to broadcast an audio signal by modulating an RF carrier frequency.
Broadcasting the signal directly as a radio wave would likely result an a signal too weak to detect, unless you had a transmitting and receiving antenna the was very large (hundreds of feed) or the transmitter and receiver are very close.

Your tape recorder experiment involved hearing the audio modulation on an AM RF signal.
It has nothing to do with transmitting an audio signal without an RF carrier.

 

[Delta Prime]

A professor once told me; there are three types of knowledge in this world.
1. What you know you know.
2.What you know you don’t know.
3.What you don’t know, you just don’t know.
The third type is the most dangerous.
As there is no way to prepare or defend against.
I believe you have picked a topic that you truly show interest in .
Here you go, kiddo …
ARRL Amateur Radio Education

 

[AnalogKid]

Your professor was paraphrasing Confucius.

CHAP. XVII. The Master said, 'Yu, shall I teach you what knowledge is? When you know a thing, to hold that you know it; and when you do not know a thing, to allow that you do not know it;-- this is knowledge.

Confucius (September 28, 551 – 479 BC)

---

I love the ambiguity in the American version:

Know what you know, and know that you don't know what you don't know.

ak

 

[Delta Prime]

Your professor was paraphrasing Confucius

Indeed, he was paraphrasing Confucius. My professor of mechanical engineering had one digit remaining on both hands,it was my first introduction to Confucius;
I was 16 at a time.
To this day, I study and reference the post you have made across various electrical , electronic engineering sites. I have used your circuit solutions That you give freely to others by request.Thank you..
-Delta Prime

 

[ofosot69]

A professor once told me; there are three types of knowledge in this world.
1. What you know you know.
2.What you know you don’t know.
3.What you don’t know, you just don’t know.
The third type is the most dangerous.
As there is no way to prepare or defend against.
I believe you have picked a topic that you truly show interest in .
Here you go, kiddo …
ARRL Amateur Radio Education

I actually know about carrier wave but I just need to confirm whether without that is it possible using magnetic field instead.

 

[Delta Prime]

I actually know about carrier wave but I just need to confirm

Confirmed! You would not have asked this question; if you knew about carrier waves?
It is rare to learn from the top down.
Unless you’re like me…
You’re asking silly questions.
Danger!
Here be dragons!!

 

[Delta Prime]

 

[ofosot69]

Confirmed! You would not have asked this question; if you knew about carrier waves?
It is rare to learn from the top down.
Unless you’re like me…
You’re asking silly questions.
Danger!
Here be dragons!!

My question was not related to radio transceiver but about audio amp. You are just trying to show yourself to be an expert without being able to answer my question properly.

 

[Delta Prime]

My question was not related to radio transceiver but about audio amp

Apologies ; just forget everything I said.thank you.

You are just trying to show yourself to be an expert without being able to answer my question properly.

This is true!

 

[bertus]

Hello,

For radio transmissions you always need a modulation scheme.
There are ULF and SLF methods that are in the audio range.

Ultra low frequency - Wikipedia

en.m.wikipedia.org

Super low frequency - Wikipedia

en.m.wikipedia.org

Bertus

 

[Delta Prime]

That’s funny. I never heard (ELF) Extremely Low Frequencies.

 

[bertus]

That’s funny. I never heard (ELF) Extremely Low Frequencies.

That is because they are electro magnetic waves in stead of audio waves.

Bertus

 

[Delta Prime]

That is because they are electro magnetic waves in stead of audio waves.

Bertus

I know.

That’s funny. I never heard

That is what makes it so funny…

 

[danadak]

This might help in determining effects of E field reduction, magnetic preponderance -

16.4: Energy Carried by Electromagnetic Waves

Electromagnetic waves bring energy into a system by virtue of their electric and magnetic fields. These fields can exert forces and move charges in the system and, thus, do work on them. However, …

phys.libretexts.org

Regards, Dana.

 

[ofosot69]

That is because they are electro magnetic waves in stead of audio waves.

Bertus

Thank you, Bertus. You made my day! I guess, it's then possible to transmit digital signals using audio amp without the need of any modulation. Moreover, lower the wavelength, further goes the transmission.

 

[bertus]

Hello,

ELF and SLF still use a kind of modulation technique.
They are used for very slow digital signals.
You can not send high speed digital signals with them.

Bertus

 

[danadak]

Amateur Radio operators do significant experiments around 2200M band.

Internet Archive: Digital Library of Free & Borrowable Texts, Movies, Music & Wayback Machine

archive.org

Propagation : https://archive.org/search?query=radio+propagation

Regards, Dana.

 

[danadak]

Page 393 on discusses propagation very low freq signals.

Internet Archive: Digital Library of Free & Borrowable Texts, Movies, Music & Wayback Machine

archive.org

Knight