Demonstrating the Effect of Decoupling Capacitors

I was assembling the 74HC4060 based oscillator for the K0LR LOWFER transmitter, and forgot to install decoupling capacitors. The effect on the output square wave quality was so visible I thought it might make an interesting demonstration.

K0LF's circuit can be found at http://www.nutstreet.net/k0lr/lftx.htm

Category:

Science & Technology

Tags:

• decoupling capacitors
• lowfer transmitter
• 74hc4060
• K0LR
• part 15

[lochinvar00465]

Very good demo. Take that from an old Navy radar tech. I too have had an interest in the 160-190 Khz band for a long time.Glad to see that the old hands-on techniques are not getting lost.

[yoududeuser]

I posted a video response which explains where the noise comes from and why bypass capacitors help.

[flopski]

If the ic suddenly draws more current, the voltage over the internal resistance in your voltage source rises, and less voltage is delivered at the terminals. 

[viewgsm]

I argue with that :

1- your chip is generating signal with some frequency

2- that signal can find its way back to the rest of the design via the power line VCC

3- you use decouple cap to DECOUPLE the noisy circuit from the rest of the design

4- choose decouple cap with value that adopt to the noise signal you expect

[whisk0r]

Nice demonstration! It's good to see an example of what voltage sag looks like in practice.