Dangerous Prototypes

In development => Project logs => Topic started by: Markus Gritsch on October 03, 2011, 01:13:23 pm

Title: Simple AM Radio Signal Generation
Post by: Markus Gritsch on October 03, 2011, 01:13:23 pm
Hi,

about a year ago I experimented a bit with directly generating an AM radio signal using an Arduino.  Here is a short video of the working setup:

http://www.youtube.com/watch?v=y1EKyQrFJ-o (http://www.youtube.com/watch?v=y1EKyQrFJ-o)

In the YouTube comments someone asked about the firmware, so here it is, attached to this posting.

The schematic is rather minimalistic:

[attachment=2]
Have fun,
Markus
Title: Re: Simple AM Radio Signal Generation
Post by: sqkybeaver on October 03, 2011, 04:43:39 pm
i would love to have seen this a week ago,

how was the sound quality?

could you hear the signal on adjacent channels?(how wide is the signal)
Title: Re: Simple AM Radio Signal Generation
Post by: Markus Gritsch on October 03, 2011, 04:49:19 pm
The sound quality is mediocre, as you can imagine :)  But you can listen to the received signal in the YouTube video for yourself. The signal was several MHz wide, which is also demonstrated in the video :)
Title: Re: Simple AM Radio Signal Generation
Post by: sqkybeaver on October 03, 2011, 04:54:07 pm
i thought that may be the case, you creating the carrier with the same output as the amplitude.

with a signal that wide i bet it went away after a few meters.

i bet this could be improved with a second output and an r/c filter and transistor.
Title: Re: Simple AM Radio Signal Generation
Post by: Markus Gritsch on October 03, 2011, 04:59:20 pm
You are right about the signal strength, and of course things could be vastly improved by adding additional circuitry.  But then I would rather FM modulate some carrier.  However, this was just done for fun and as a proof of concept :)
Title: Re: Simple AM Radio Signal Generation
Post by: sqkybeaver on October 03, 2011, 05:11:00 pm
this is right up my alley,

i have an dev board with an 100MHz 8051 that would work well for this. the pca can output an square wave up to 50MHz with a simple mixer and the 500K sample dac any frequency in the 10 meter band could be simulated using an linear equation in the micro.
Title: Re: Simple AM Radio Signal Generation
Post by: hak8or on October 05, 2011, 05:19:14 pm
I always wanted to learn how to do RF, but I have not been able to understand it for a year now.
This seems like an awesome idea, I never knew that you could make AM with a arduino! I thought you would require many additional passive's to get anything in the RF spectrum.

So essentially you are creating a 734 KHZ wave from the antenna? How is it several MHZ wide then?
My apologies if I am getting off topic.
Title: Re: Simple AM Radio Signal Generation
Post by: Markus Gritsch on October 05, 2011, 05:32:09 pm
My mistake.  Should have written kHz :)
Title: Re: Simple AM Radio Signal Generation
Post by: AdShea on October 05, 2011, 10:29:35 pm
It should be a few kHz wide as you're mixing it with a few kHz bandwidth signal.  In the limit as you're sampling at 34kHz you could have a 17kHz wide AM signal transmitted.  Broadcast AM usually is only a few kHz wide and is band-limited to just over telephone quality.
Title: Re: Simple AM Radio Signal Generation
Post by: hak8or on October 06, 2011, 12:12:43 am
Ah alright, thanks for the clarification guys! :D

Good luck with your final application of this proof of concept!