Demonstrating the Effect of Decoupling Capacitors

April 7, 2011 | Amateur Radio, electronics | By: Mark VandeWettering

I’ve been interested in LOWFER radio (low frequency radio operation) for quite some time. Under Part 15, unlicensed experimenters can transmit signals in the frequency band between 160khz and 190khz, subject to certain regulations on power and antennas. You can read more about it here.

I was bored the other day, so I decided to breadboard the oscillator section of K0LR’s Simple LOWFER Transmitter. It’s basically a crystal oscillator that is tied to a 74HC4060 Oscillator/Divider. To transmit on LOWFER frequencies, you might use a 6Mhz crystal and divide it by 32, creating an output around 187khz. I didn’t have a 6Mhz crystal (or really any of the other right components), but I had close values, so I put the circuit together with what I had.

And saw lots of noise in the output waveform. The high and low values were probably wavering by several tens of millivolts. I then remembered that I hadn’t installed a decoupling capacitor. Since I hadn’t seen anyone demonstrate the effect of decoupling capacitors, I thought it was interesting enough to tack together a quick video.

K0LR’s Simple LOWFER transmitter

Comments

Comment from K6EF
Time 4/7/2011 at 10:36 pm

Hey Mark,

I’m just kinda getting into circuits as well and found your blog to be a great resource.. I only realized later that we hang out at the same conference once a year. 🙂

If you’ve never met Bonnie Crystal (KQ6XA) you should.. She does a bunch of LOWFER stuff I believe.. Her website is http://www.qsl.net/kq6xa/

She’s a local.

73s de K6EF

Comment from WA5PSA
Time 4/9/2011 at 10:56 am

OK. I’ve been a ham since 1966 – and I finally understand what decoupling capacitors do. Heh. Thanks!