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• More experimentation!

  KD9KCK • 10/27/2017 at 15:53 • 0 comments

  Recently I have been doing some more experimentation with this. 

  FM changes frequency moving from one to another based on the input audio signal.  This movement means that the amplitude at a frequency will change as the transmitter moves over it to follow the audio. This change in amplitude is what allows AM demodulation to hear a scratchy version of the FM signal. 

  The next step is to try demodulation multiple areas of the FM signal with AM to get more of the total FM signal.

• A Theory!

  KD9KCK • 01/11/2017 at 02:07 • 0 comments

  During some of my free time I have developed a theory as to why you can receive FM using AM demodulation. This theory uses a little bit of physics and also some thinking about different ways to plot signals.

  First most of the time when we see a plot of AM and FM signals it is Amplitude plotted against Time.

  This is how we can see the Amplitude of AM changing and the Frequency of FM changing. But what if we decided to plot them Time against Frequency. We see that AM is basically a straight line. While FM moves about left and right of its center Frequency. Now lets think for a moment if we placed a box over part of the FM signal. We will see that the signal crosses this box. The lines in the box can be looked at as the area AM would see. The lines in the box are a higher Amplitude then the areas with no lines. The Amplitude indeed is modulated bu the fact that the Frequency is changing. This changes the spacing between the line in the box which is a change in Amplitude. I will enclude a few picture of what I am talking about.

• Further investigation.

  KD9KCK • 12/06/2016 at 15:07 • 0 comments

  Upon further investigation I have found that that for some reason the signal's amplitude follows the frequency. One idea for the cause of this is as the frequency shifts left and right of the center freq the power at that frequency slowly dissipates causing a modulated affect.

  
  

  The diagram below shows what I believe to be the cause of it.

  (PLACEHOLDER)

• Noticing something strange...

  KD9KCK • 12/06/2016 at 02:21 • 0 comments

  About 6 months ago when I first got my SDR (Software Defined Radio) I noticed that if I set it to do AM demodulation I was able to still hear the FM station I was listening to. An example is included here.

  FM Station

  http://cdn.hackaday.io/files/18808804681472/FM.mp4

  FM Station with AM demod

  https://cdn.hackaday.io/files/18808804681472/AM.mp4

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