I'm trying to listen to the CPU freq's my PC produces (kinda similar to what was done here: https://github.com/fulldecent/system-bus-radio)

I do see a clear signal that comes from the CPU (I know that because I can control it by reading memory blocks), however the distance it transmits to is very short (~20 cm).

  • Is there anything I can do to see the signal from a greater distance?
  • Does it depend on the antenna ? (will a longer antenna produce better results)
  • Does the shape of the antenna makes a difference ? (should the wire be folded into a circle or is it better as a long straight wire)

I'm using a random wire antenna (~60 cm long made into a circle)

The dominant signal is at ~300KHz - 450Khz and I'm using SDRPlay2

  • $\begingroup$ Welcome to Amateur Radio SE. Be sure to take the tour at ham.stackexchange.com/Tour to get the most out of the site. As for your post, Didja Know that an AM Radio was the very first I/O peripheral for personal computers? It was used with the Altair 8800 with appropriate code to play music. The fist song was called "Daisy" (Bicycle built for two). Check out this search: google.com/search?newwindow=1&q=altair+plays+daisy - it was so popular that the modern Altair emulators are built so they can run the same code to generate the same signals. $\endgroup$
    – SDsolar
    Commented Jul 27, 2017 at 1:19

1 Answer 1


In general, the length and shape of an antenna has a profound effect on the amount of power the antenna makes available to the receiver. Matching the impedance of the antenna system to that of the receiver ensures that the receiver can take advantage of the power that the antenna system delivers.

At the low frequencies in which you are interested, I would consider a multi turn antenna on a ferrite rod core. You may have some success by extracting one from a discarded AM broadcast receiver. The impedance of this antenna will likely not match that of your SDR receiver but it may prove adequate for your needs. You could also purchase a ferrite rod and wind your own.

You could measure the antenna impedance with an antenna analyzer and construct a simple matching circuit if needed. Your local ham radio club would likely make an antenna analyzer available to you. If you then need help with the matching circuit, just post back a new question on this site.


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