Activating (sort of) Lake Thunderbird (K-2792) with a homebrew transmitter
Sam Duwe WN5C
When I dove into radio a couple years ago a few sub-hobbies caught my attention: QRP, portable ops, CW, and homebrew. Of course, these all fit nicely together, but in my mind there was a huge leap between soldering an unun and a building a radio. But why not try? What’s the worst that could happen by melting solder and then sitting at a picnic table? This is how I built a simple transmitter and kind of activated a park.
The Michigan Mighty Mite
Nearly everyone has heard about the Michigan Mighty Mite (MMM), a QRPp transmitter popularized by the Solder Smoke blog. There are countless YouTube videos and posts across the internet. It’s very simple: a single transistor, a variable cap, a coil, a crystal and some resistors and a cap. Supposedly one can get up to half a watt of output (I couldn’t). But with a small purchase from Mouser one can oscillate. That seemed pretty cool.
I hadn’t touched an iron until I started playing radio. But I’ve been drawn to homebrew projects. I built a regenerative receiver last year which was very rewarding. I’ve also put together kits (a QCX mini and a TR-35). But my dream has always been to construct a transmitter/receiver combo, or a transceiver. I thought a good place to start was the MMM.
I built the transmitter based on the common schematic for the 40-meter band. The MMM is crystal controlled but I opted to solder in a socket and buy a handful of crystals, so I have the luxury of operating on 7056, 7040, and 7030 kHz. I made a few other improvements, too. The first was to build a low pass filter to attenuate harmonics. Second, although I haven’t finished it yet, the switch on the right will be to choose between multiple crystals. And third, I added a BNC jack to connect a receiver, with a transmit switch. When not in use the transmitter will dump into a dummy load. This receiver switching idea was lifted from the design of the MMM that QRP Guys produces.
When I tested the transmitter at home the best I could get with my charged Bioenno 3 Ah battery was about 300 mW output. The filter is reducing things somewhat, but maybe I need to look into a different transistor or rewind the coil. But I was able to get a 339 signal report from Illinois (no sked) in the midst of distance lightning crashes, so I had a little confidence going forwards. School is out for me this summer, so I decided to head to the park.
Lake Thunderbird State Park (K-2792)
I activate Thunderbird all of the time, but only rarely on 40 meters. I’ve been doing that more though because I’m slowly realizing that DX (relatively speaking) isn’t everything and it’s nice to connect with the local guys. I arrived at about 9:00 AM and set up the rig. I chose my QCX mini (tuned for 20 meters) as the receiver because it’s less sensitive out of band and I didn’t want to overload my ears. A 3 Ah Bioenno battery powered everything, and I used my CW Morse key.
My antenna is an compact 40-meter EFHW based on HB9EAJ’s design. It’s cut for 20 meters with a 17-meter band link and has a 34 uH loading coil with an additional 6-ish feet of wire. It’s not as efficient as a full-length EFHW but it sure is easier to deploy. I was able to use my throw weight/line to get it up about 30 feet up into a tree, and have it slope down to the picnic table overlooking the lake.
I pulled out my 7056 kHz crystal. My wattmeter said, even after fussing with the capacitor, that I was going to have to be comfortable with only 200 mW of output. The conditions were okay but not great. Within a few moments of CQing I was spotted (poorly) by the RBN and my friend and Elmer, Perry (N5PJ), called me back. He’s 30 miles away but reported that the “9” in 229 was real; I was transmitting cleanly!
In the next hour of pounding away on the straight key I made contacts in northeastern Oklahoma, north Texas, Missouri, and Kansas. A few of the signal reports were good, conditions were up and down. But it was working! Manually switching between TX and RX wasn’t as difficult as I thought, although I have never worked so hard for POTA QSOs.
After about an hour and a half I had racked up five contacts. My call had fallen off of the RBN and things weren’t looking good. I decided to finish the activation on 20 meters with my TR-35 at 5 watts which I did in short order. The bonus that Randy N5ILQ was also unknowingly activating very closely (just beyond the bridge in the previous picture). We had a booming 17-meter (same) park-to-park QSO.
Like Thomas showed, QRPp is totally doable and very fun. I think that if I were at the park on a different day, or began earlier, I would have completed the activation using the MMM. But in this case 10 contacts wasn’t my yardstick for success; instead, making any contacts with a transmitter and antenna I built from scratch was a win. I’ve had many memorable POTA outings, but this tops them all.
I’d like to build a 20-meter version to extend the net a bit further. I also think that experimenting with other transmitter designs would be fun. And if I build a 40-meter receiver I could realize my dream of having a complete homebrew kit and look even nuttier at a park bench.
This has been a fun project and deployment. I can’t recommend enough building a MMM and trying it out, and if you’re in a 300-mile radius of me I hope to hear you on the air!