Low power operation and homebrew

I’ve always been fascinated with leveraging the benefits of computing and electronic communications without consuming too many resources in the process.  I feel, deep inside, that if it isn’t sustainable, that it will likely go away.  Think Rome.

With that said, I recently built a Michigan Mighty Mite transmitter for 40m according to the outline here: http://www.qsl.net/wb5ude/kc6wdk/transmitter.html  Honestly, to be sure I understood the schematic which has some quirks (at least to my lightly trained eye), I had to read lots of other blogs and watch some videos.  The information about winding the air core inductor was the weakest.  I think some of the lightness of documentation is because it will most likely work somewhat even if you mess it up pretty badly.  So, this marks my first ever homebrew transmitter!

Michigan Mighty Mite transmitter wired on a breadboard.
This is the first homebrew transmitter I’ve built. It has been an adventure.

Testing it involved my first homebrew dummy antenna (or dummy load, depending on your vernacular) a pair of 100 ohm resistors in parallel inside a 6oz tomato paste can.

A pair of 1/4 watt 100 Ohm resistors in parallel connected to alligator clips at the bottom of a 6 ounce tomato paste can
This is my first run at assembling a dummy load to prevent this transmitter from radiating its signal far.  No, the leads are not touching the can 🙂

Then my first homebrew low pass filter to attenuate the higher frequency harmonics.  I followed the recipe for 40m here: http://www.gqrp.com/Datasheet_W3NQN.pdf

ceramic capacitors and hand wound ferrite torroid inductors arranged as a low pass filter for 7MHz ham radio operation
Simple LC harmonic, low pass, harmonic filter for 40m

The one site on the Michigan Mighty Mite I encountered suggested the input voltage be between 10 and 14v.  Mine didn’t work when I first assembled it on the breadboard so I wondered if maybe my 9v battery wasn’t enough to start the oscillator (noobs, huh?). I was pretty sure that wasn’t true, but not understanding the theory enough yet, I couldn’t rule it out.  So I threw together a homebrew LM317 based linear power supply.  I set the voltage to 10.7v and it still didn’t work.

Then I got down to the business of triple checking my connections and trying a little rearranging of some connections to shake things up a bit.  When I triple checked every connection and made sure I was following the schematic 100%, sure enough, I got it to work.  One homebrew project turned into four.  Now I have four interchangeable modules that can be put to use in other projects and I’ve learned a lot while refreshing some of my skills like reading datasheets, soldering, and translating schematics to a breadboard.

Bottom line: this was an adventure and, since I knew it would take some hard work and time, I did not get frustrated.  I just set my mind to work through each challenge and learn from their solutions.  This was a HUGE success for me.

What’s more, I feel a strong push to follow this super low power ethos and see where it takes me.  I’m used to thinking of low power as laptop vs. desktop.  Raspberry Pi vs. Laptop.  Baofeng vs 100watt desktop transceiver.  The thing I was reminded of here is that fundamental, empowering, and exciting communications can take place with mW and mA from small dc power supplies (ex. very small solar panels or 9v heavy duty batteries).

Here’s the parting shot of my fully prototyped transmitter

A breadboarded Michigan Mighty Mite transmitter with an external breadboarded LC filter feeding a dummy load in a tomato paste can all keyed by a keyer made on a slice of maple sapling with a strip of flattened copper pipe
Building this was an adventure. I’m so glad I tried the mighty mite first.

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