Today’s task – because 16 inches of snow fell in the last 24 hours – was to work on the power supply for my homebrew radio. I’ve got a bunch of LM317 regulators lying around so I decided to use one of them. Needed to play around with multiple resistors to get the right settings (12 V in, 5.2 V out). Predicted output was 5.12 V based on the resistor values used, actual was 5.18 V.
And just in case you didn’t believe me about the snow, here’s my backyard:
It seems that I often look for ways to procrastinate from preparing for classes, and this semester is no different. Well, it is different in the sense that to delay my writing exams, I took an exam. Yesterday, I passed the the examination for the amateur radio technician class license.
Soon, I’ll be able to start transmitting in a few amateur bands (one has to wait until a call sign is designated by the FCC and that information is published in their database. Meanwhile, I am keeping myself busy with building a radio. There are plenty of instructions on the web, and the biggest challenge has been poring through all of the available designs and identifying a build that works for me.
For my first build, I want a technician class device that can do both voice (SSB) and Morse code (CW). That means I will need to focus on the 10 meter band, since that is the only set of frequencies where technicians can transmit both SSB and CW. It’s not used nearly as much as the 20 and 40 meter bands used by general class operators, in part due to the limited long-distance (DX) communications possible. That may change, though, with solar cycle 25. Solar activity interacts with Earth’s atmosphere such that HF frequencies (between 3 and 30 MHz) tend to propagate farther. With sunspot activity expected until about 2030, it seems to be a great time to advocate for DIY 10 meter band radios.
I’m a long way from building a complete device (or even really talking about it), but I’ll share a teaser.
That’s an Adafruit M4 Express in concert with a Si5351 frequency generator, SA612 mixer, a class D amplifier and a rotary encoder for tuning. Once I connected it to an antenna, I was able to dial into an amateur frequency in the 40-m band (note – anyone can build and use a receiver, the license is required only for transmitting) and hear a ham in nearby Rochester. Pretty exciting for me given that there’s no filter or amplifier on the antenna, which in this case was just a long coax cable.
And so it begins! I’m sure the rest of the semester will be filled with last minute lecture preps and piles of ungraded lab reports on my desk. I’ll gripe about them with anyone who wants to listen in on 10 meters.
I tried a different approach to my Instrumental Methods course this semester, which culminated in students building their own heart beat monitor using the Adafruit Feather M4 Express microcontroller. The project is an adaptation of this one from Analog Devices. The main part of the project was for students to add a voltage divider (which they have seen and used in previous projects during the semester), build the circuit on a breadboard and adjust a few of the components in light of the different voltage (3.3 V vs 5 V). Each student was successful in developing a device, and one was able to confirm that the pulse rate was consistent with the fit bit he was wearing.
Previously, I announced my latest project in The start of FeAtHEr-Cm. Over the past several weeks, I’ve been iterating through the potentiostat design and I think I’m at a point that the design will stay more or less in place, allowing me to shift my focus to documentation, instrument use and lesson plans.
I’ve also spent some time building a website that contains the documentation for building the instrument, writing code and using the potentiostat in an educational setting. Rather than re-write all of that information here, head on over to this page for a summary of what’s been done and what’s in the pipeline.