I was having a noise problem with my NE602 Si5351 OLED display receiver. There was an annoying high pitched whine in the audio output. The source was easy to identify: If I reached in and unplugged the OLED display, the noise disappeared. Next I had to find out how the OLED noise was getting into the rest of the receiver. It could have been through the SCL SDA or even the ground lines. It could have been just through capacitive or inductive coupling from the display board itself. A big clue came when I tried powering the display from a completely separate power supply: BINGO! The noise disappeared. So I knew the noise was going into the rest of the receiver through the Vc line that powered the OLED. I had been powering the OLED from the 5V regulator on the Arduino Uno. In an effort to isolate the noise, I put a separate 5V regulator in the circuit for the OLED. No joy -- noise still there. I then tried putting an RC low pass filter between the OLED and the 5V regulator. Still had the noise. Finally I remembered something from the AF AMP circuits of Roy Lewallen, Rick Campbell and Roger Hayward. ( I think Roy was the pioneer on this one.) They all used an "active decoupler" between the first AF amp and the power supply line. I confirmed that it was my first AF amp that was picking up the OLED noise. I built the active decoupler (just three parts!) and the noise disappeared. GONE! There are only three parts, but the way this circuit works is kind of complicated and not very intuitive. There is a good discussion of how it works here: www.facstaff.bucknell.edu/dkelley/elec351/Lab/elec351lab5_sp04.doc Roy, Rick and Roger were using this circuit to knock down 60 Hz AC hum, but I found that my OLED noise was at around 200 Hz -- I figured (correctly) that the active decoupler would take care of this as well. I think this little circuit can be useful in dealing with the kind of noise generated by the digi displays that many of us are now using. David Rowe has a really interesting analysis of this circuit here: http://www.rowetel.com/?p=4781
In response to popular demand, "SolderSmoke -- Global Adventures in Wireless Electronics" is now available as an e-book for Amazon's Kindle.
Here's the site:
For the print version:
For shipping from a printer in the U.S. (probably better for N. American buyers) Click here: SolderSmoke USA Version
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Click here: SolderSmoke EU Version
The two versions are identical, except for a minor difference in the paper used. That's why the prices are a bit different.
Bill's OTHER Book (Warning: Not About Radio)
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W4HBK's QRSS Grabber: The Amazing Pensacola Snapper (Live!)