Things We Learned: The Value of Capacitors when RF is Floating Around

Squigily audio in our homebrew ham radio rig? Capacitors!

This extends the capacitor post from last week. This week, while adjusting the Tuna Topper amplifier bias after a run-in we had with an unexpected rain shower, I put capacitors across the dit and day switches on the keyer. The dit capacitor was particularly useful because with the amplifier bias set above a certain level, the keyer chip would immediately reboot when the dit key was pushed. I'm assuming RFI transients were punching through to the little processor, befuddling it in the process.

Today, the kid—Diaze—and I changed the battery from a D cell pack to a LiFePO4 battery. The extra bit of punch provided by the nicer battery meant we had to turn down the bias on the TunaTopper's onboard pot just another quarter turn or so. The resulting keying sidetone over the headphones was less than esthetically pleasing though.

When Diaze sat down to key out a CQ, the buzzing and squiggly sounds were too much for her. A recent episode of the Ham Radio Workbench podcast had mentioned adding a capacitor between the headset line and ground to fix an AM radio station problem one of the hosts experienced. I'd tried with a smaller value of capacitor earlier in the week with no luck. Today, we placed the largest capacitor we had at hand—100 nF—between the headphones and ground, and Wow!

The sidetone sounds so much better! In addition, one particularly loud hum that's coming from somewhere in the neighborhood during daylight hours is gone as well!

Here's what it sounds like post-capacitor

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