Over the last couple weekends, I put together an RF signal generator based on a AD9850 DDS module controlled by an ATmega328 microprocessor. In this entry, I describe both physical construction and the arduino sketch underlying its operation. The most recent versions of both code and schematic are archived on github.
Category: QRP
Madagascar Mighty Mite Experiments
On one hand, it probably doesn’t make too much sense to try to refine the MMM: it’s more an oscillator demo than a building block of any more complex radio, but there are a couple variables that I thought would be fun to explore: choice of transistor, supply voltage and emitter resistor value. Tables and pretty x-y graphs follow.
The MMMM Receiver
The 80m Madagascar Mighty Mite was suffering from “a tree falls in the forest but nobody hears it” syndrome. Eighty meters is a tall ask for Madagascar — there aren’t that many hams in the coverage area, and given local noise, I doubt any of them can hear well on 80m. It would be a long wait for a signal report about the on air performance of the MMM. Clearly, the thing to do was to create a mate for the MMM, the Madagascar Mighty Mite Mate (MMMM).
In keeping with the philosophy of back-to-basics rockbound simplicity, I decided to build an 80m version of the Sudden Receiver originally described by George Dobbs in SPRAT, and reprinted in 73 (October 1991, page 8, available online thanks to the Internet Archive).
The Topper Amplifier Revisited
I thought my 200mW Madagascar Mighty Mite (MMM) would benefit from some sort of afterburner, so I dusted off a project shelved in 2011: the Texas Topper amplifier. I had built based on a design by Chuck Carpenter and kitted by Rex Harper. I ran into a couple problems back then, including some difficulty getting the bias right on the mosfet at the heart of the amplifier. In another brilliant move, I managed to burn out said mosfet by grounding it while trying to get it and its heat sink to fit into a metal box.
The Madagascar Mighty Mite
Over the last few years, there have been a spate of postings from homebrewers taking inspiration from the Soldersmoke podcast to whip up various incarnations of the Michigan Mighty Mite, a very simple rock-bound QRPp transmitter. I’m a little late to the party, but here’s my story.
SOTA W3/PT-001: Mt Davis
My final SOTA stop on the way back to Washington, DC from Indiana was at Mount Davis, the highest point in Pennsylvania. Arriving towards the end of the day, I did not take advantage of any of the hiking trails from around the mountain, but followed signs directly to the parking area. A path leads around to a metal observation tower and a path continues past the tower to a sort of rock garden with some informational plaques. Not far from the tower’s base, there are some large boulders, where I set up the radio.
SOTA W3/PT-004: Sugerloaf Knob East
Yes, yet another Sugarloaf. I guess sugarloafs were very popular for long time and people saw them wherever they looked. I activated this Sugarloaf on the way back to Washington, DC from Indiana. This and several other SOTA summits are clustered near the Ohiopyle State Park. I have camped and white water rafted there a couple times in the past, but due to time constraints, I didn’t have much time to hang out in the park proper on this trip.
SOTA W8O/NE-001: Noblet Benchmark
On the way back towards Washington, DC from Indiana, I passed again through Ohio, this time to the south of the outbound route. I had targeted two SOTA peaks near Ashland, Ohio: W8O/NE-001 (Noblet Benchmark) and W8O/NE-003 (the Ashland County High Point). I did get to both sites, but only activated the former one. Both are discussed, below.
SOTA W8O/NE-007: Summit County HP
West of Pittsburgh in the direction of Chicago, the SOTA summits are few and far between, and what summits there are subtle, more like slowly graded hills than mountains. However, the Summit County HP, while not a eagle’s nest view, was my favorite summit from this trip.
I felt like I knew this town before I got there from looking at aerial photos and even “driving” some of it using Google Street View. The summit area is wide and flat, so there were a lot of options about where to pitch the antenna: the actual county high point, which is marked along the main road? In the trees behind the cemetery near a commercial antenna? In the parking lot of the Sikh Temple? Or in a park.
SOTA W3/SV-019: Emmaville Mtn North
Continuing with activations on the way out to Indiana from Washington, DC, the next stop was Emmaville Mountain North, SOTA W3/SV019. The peak is on public property that can be accessed by following Bark Road. When I exited Interstate 70, my phone’s GPS initially wanted me to take Bark Road southwards and wrap all the way around. That didn’t make sense, since going the other way was shorter, so I ignored my cell phone GPS and went up the shortest way. Continue reading “SOTA W3/SV-019: Emmaville Mtn North”