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Why Does My Transmitter Hum?

Because it doesn't know the words!
     Or, it could be that you are suffering from one of several technical causes of hum in transmitter circuits...
     According to those in the know, these causes might include:
  • Power supply hum due to poor DC supply filtering
  • AC hum pickup in the transmitter audio due to poor shielding
  • Ground loops
  • RF induced hum modulation on the transmitted signal
What's the cure? Here are several links to technical articles dealing with hum reduction in audio and RF circuits:

Editor's note:  Dead links were recently updated with links to the original content found at the awesome, link saving Internet Archive!

Finesse Voltage Regulator Noise! from Wentzel associates
Hum reduction info from
Hum redux, from
Sound Card Interfacing from
Hum Rejection from
"Tweaks" - bottom of the article
Ground loops from
Breaking ground loops from
Hum Update from
Circuit tips - middle of the article
Power and grounding techniques
RF/RFI & Grounding

Happy Hum Hunting!

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