How Can I Create a Low Frequency Radio Transmitter Using a Speaker?

[gabrielshier]

Hello,

Lately i have came across an interesting article. Currently i am interested in synthesizing a long wavelength (3Hrtz, 9 Hertz or 12.5 Hertz) at a strong power. The transmitter circuit can be of low voltage which will later on be converted by a multiplayer to a strong signal (which is not a problem). My difficulty is to make that radio transmitter which will create such low frequencies.
Any ideas?

Thanks...

 

[jambaugh]

Off the top of my head I see three means beyond the classic RCL circuits you'll find in your standard transistor circuit cookbook.

DSP: Use a PC or microcontroller with D/A converter to produce the signal. (Your trusty laptop can output this via the headphone jack using suitable freeware. Google search: freeware, function generator).

Electro-mechanical 1: At such low frequencies you should be able to build a mass spring system with magnetic pickup and amplified feedback.

Electro-mechanical 2: You could spin a small magnet with a variable speed motor within a magnetic loop at 3, 9, or 12.5 rpm and you'll get a resulting oscillating electrical signal. This should produce a pretty clean sine-wave.

The oscillator is no real problem, you are talking about the low end of audio frequencies and indeed subsonic. So think "Audio frequency" in this setting. For example try a google search of the terms "analog electrical circuits tone generator". The hard part may be getting a good sine waveform at these low frequencies without producing harmonics.

 

[berkeman]

Hello,

Lately i have came across an interesting article. Currently i am interested in synthesizing a long wavelength (3Hrtz, 9 Hertz or 12.5 Hertz) at a strong power.

What do you plan on using for an antenna? You must own a lot of land! Also, keep in mind that pretty much the whole radio spectrum is protected by federal and international law. You can't just make a transmitter and start transmitting at any old wavelength. What are the applicable laws that you are aware of for this wavelength?

 

[gabrielshier]

Jambaugh, first of all, thanks for the quick response.
The second option sounds the best. A clean good sine wave is exactly what i need. Could you please explain about the practice of it? With the magnetic flux i am quiet familiar.

 

[dlgoff]

"What do you plan on using for an antenna?"

Let's see. Length of a full wave antanna = ((186000miles/sec)/3Hz) = 62000 miles. Is that right. That's really long.

 

[gabrielshier]

"What do you plan on using for an antenna?"

Let's see. Length of a full wave antanna = ((186000miles/sec)/3Hz) = 62000 miles. Is that right. That's really long.

And who said I'm going to use an antenna? Aren't there different other kind of wavelength transmitions?

 

[dlgoff]

If you want an EM emission, you need to match the transmitter output to something than can radiate.
Check out the size of these antenna. They are/were used for frequencies in the hundereds of kilohertz. Now think about your long waves at 3Hz.

 

[gabrielshier]

Output

The output is not radio or any antena depending system. The answer to my question i received with the best solution i could hope for. The computer based function generator will be the best solution. The only problem i have now left, which I'm quite sure i can overcome, is how to output the function at 185dB...
Just not sure how accurate the function generator output is throught the computer phone jack.

 

[Ouabache]

Hello,

Lately i have came across an interesting article. Currently i am interested in synthesizing a long wavelength (3Hrtz, 9 Hertz or 12.5 Hertz) at a strong power.

Very interesting question! I wonder what article are you reading? Perhaps you can fill us in on more information about your plan. Do you want to transmit this LF signal over a distance? Approximately how far? Do you also want to hear this signal on a radio reciever?

 

[gabrielshier]

Very interesting question! I wonder what article are you reading? Perhaps you can fill us in on more information about your plan. Do you want to transmit this LF signal over a distance? Approximately how far? Do you also want to hear this signal on a radio reciever?

The function will be transmitter via a speaker and not using an antenna. The max distance the function will need to be traveling to is 20 meters. The problem now is finding a speaker that can output such low frequencies.

 

[berkeman]

The function will be transmitter via a speaker and not using an antenna. The max distance the function will need to be traveling to is 20 meters. The problem now is finding a speaker that can output such low frequencies.

Ohhhh. Audio. I get it now. We were thrown off in your original post (OP) where you said this:

My difficulty is to make that radio transmitter which will create such low frequencies.

So now my comments about you needing a lot of land for the antenna and permission from the FCC and Navy are no longer applicable. Just be careful where you point that big-old speaker at 180dBA !