The personal website of Scott W Harden

Microcontroller Clocking a Transmitter?

I shouldn't claim this idea as novel. After googling around, I found another person who's doing the same thing, and now that I read his page I remember reading his page before, which is likely where I got the idea in the first place. I want to give him credit and hope that my project can turn out successfully like his!

Here's my idea: The core of any transmitter is an oscillator, and in simple transmitters (like QRSS devices), it's often a crystal. Frequency adjustment is accomplished by adjusting capacitance to ground on one of the crystal legs. Simple oscillators such as the Colpitts design (based on an NPN transistor) are often used (pictured).

See how pins 4 and 5 allow for a crystal, and pin 6 has a "CKOUT" feature?" I'm still not sure exactly what the waveform of its output looks like. The datasheet is almost intentionally cryptic. About the only thing I've been able to discover from the Internet is that it's sufficient to clock another microcontroller. However, if it's an amplified sine wave output, how cool is it that it might be able to produce RF at the same frequency at which it's clocked?

However in my quest to design a minimal-case long-distance transmitter, I'm trying to think outside the box. Although it's relatively simple, that's still several parts just to make an oscillating sine wave from a crystal. The result still has to be pre-amplified before sending the signal to an antenna. I'm starting to wonder about the oscillator circuitry inside a microcontroller which has the ability to be clocked by an external crystal. For example, take the pinout diagram from an Atmel ATTiny2313 AVR:

Taking it a step further, I wonder if I could write code for the microcontroller to allow it to adjust its own clock speed / frequency output by adjusting capacitance on one of the legs of the crystal. A reverse-biased LED with variable voltage pressed against it from an output pin of the microcontroller might accomplish this. How cool would this be - a single chip transmitter and frequency-shifting keyer all in one? Just drop in a crystal of your choice and BAM, ready to go. Believe it or not I've tested this mildly and it's producing enough RF to be able to be picked up easily by a receiver in the same room, but I'm still unsure of the power output or the waveform. If the waveform is an amplified sine wave I'm going to pass out. More likely it's a weak sine wave needing a preamplifier still, or perhaps even amplified square waves in need of lowpass filtering...

My wife snapped a photo of me working! It's a funny pic - I'm in my own little world sometimes…

This article's source was last edited on September 10, 2020.
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Impeded Progress

Spring break is over and dental school classes have resumed. An unexpected side-effect of spending all of spring break working so hard on my QRSS VD software project is that when I resumed dental school, I actually feel more relaxed. It's like spring break was my period of intense work, and the rest of dental school is my "break". It makes me a little disappointed though - I feel like dental school isn't pushing me very hard, and I don't feel like I'm learning or growing like I could be. With the estimated cost of tuition totaling ~$200,000 for four years of dental school, I'd have expected classes to feel a little less trite. Anyhow, it is what it is, and I'll make the best of it.

I'm spending the weekend polishing-up code and reading circuit diagrams. I have a few projects on my plate (involving QRSS in some way or another) and I'm managing the transition from productivity back to dental school the best I can...

This article's source was last edited on September 10, 2020.
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W4DFU Gator Seen in Canada

I don't have long, but the picture speaks for itself. Sent from Florida to Canada. I used VE1VDM's "Big Ears Grabber" in Canada.

This article's source was last edited on September 10, 2020.
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QRSS VD version 1.04 Released

I'm proud to announce the first public version of QRSS VD has been released!

Edit: QRSS VD is now on GitHub:

This article's source was last edited on September 12, 2020.
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How to Destroy a Radio Operator

After priding myself on my ingenuity a few weeks ago for documenting my homemade stealth indoor apartment antenna for 40m and 20m, it seems that the green movement has contrived a plan to cripple my successes. So far I've made a few dozen contacts in Morse code with my humble little setup (~20 watts of power, direct conversion receiver, indoor homemade antenna). The photo shows some QSL cards I've gotten. Anyhow, my apartment manager decided that my apartment needed to have solar panels added to it. It's too early to tell for sure, but spinning the dial a few times and hearing *nothing* makes me think that it dramatically impacted my reception (and likely transmission) in a dramatic way.

There are the QSL cards I got so far:

I think the AJ4VD station has been effectively shut down!

This article's source was last edited on September 10, 2020.
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