SWHarden.com

The personal website of Scott W Harden

QRSS and Life in Dental School

QRSS uses extremely simple radio transmitters at extremely low power to send an extremely slow Morse code message over an extremely large distance to extremely sensitive receivers which are extremely dependent on computers to decode. While you might be able to send a voice message across the ocean with ~100 watts of power, there are people sending messages with milliwatts! The main idea is that if you send the signals slow enough, and average the audio data (fast Fourier transformation) over a long enough time, weak signals below the noise threshold will stand out enough to be copied visually.

Without going into more detail than that, this is the kind of stuff I’ve been copying the last couple days. The image is a slow time-averaged waterfall-type FFT display of 10.140 MHz copied from a Mosley-pro 67 yagi mounted ~180 ft in the air connected to a Kenwood TS-940S transceiver. Red ticks represent 10 seconds. Therefore the frame above is ~10 minutes of audio. The trace on the image is from two different transmitters. The upper trace is from VA3STL’s QRSS quarter-watt transmitter from Canada described here and pictured below. The lower trace is from WA5DJJ’s QRSS quarter-watt transmitter in New Hampshire, described and pictured here.

I don’t know why I’m drawn to QRSS so much. Perhaps it’s the fact that it’s a hobby which only a handful of people have ever participated in. It uses computers and software, but unlike software-defined radio they don’t require complicated equipment, and a QRSS transmitter or receiver can be built from simple and cheap components.

__Argo: __There’s a popular QRSS “grabber” software for Windows called Argo. It dumps out screenshots of itself every few minutes which is nice, but it doesn’t assemble them together (which is annoying). I wrote a script to assemble Argo screen captures together as a single image. It’s a script for ImageJ.

makeRectangle(13, 94, 560, 320);
run("Crop");
rename("source");
frames = nSlices();
newImage("long", "RGB White", (frames - 1) * 560, 320, 1);
for (i = 0; i < frames; i++)
{
    selectWindow("source");
    setSlice(i + 1);
    run("Select All");
    run("Cut");
    selectWindow("long");
    run("Paste");
    makeRectangle(i * 560, 0, 560, 320);
}
selectWindow("source");
close();

As far as life goes, I’m discovering that it’s not the attainment of a goal that gives me pleasure; it’s the pursuit of the goal. Perhaps that’s why I peruse hobbies which are difficult, and further challenge myself by doing things in weird, quirky ways. I’d love to experiment more with radio, but I don’t have much money to spend. Yeah, an all-band 100-watt HF/VHF/UHF rig would be nice, but I don’t want to spend hundreds of dollars on that kind of equipment… Maybe when I have a “real” job and stop being a student I’ll be in a better place to buy stuff like that. I built a cheap but surprisingly functional base-loaded vertical HF antenna for my apartment balcony (don’t worry neighbors, it’s taken inside after every use). It’s mainly for receive, but I don’t see any reason why it couldn’t be used for QRP transmitting.

__Yes, that’s an antenna made from copper pipe, wire, and toilet paper rolls. __I wound the wire around the base and created various tap points so it serves as a variable inductor depending on where I gator-clip the radio. Not pictured are 33’ radials running inside my apartment serving as grounding. The antenna feeds into a Pixie II direct conversion receiver / QRP transmitter which dumps its output to a laptop computer. I copied some PSK-31 transmissions from Canada with this setup. It works way better than a long / random wire antenna because it dramatically boosts signal-to-noise when tuned to the proper frequency.

UPDATE: VA3STL mentioned me on his site


HF CW on the Cheap

This is a project I intend to work on over Christmas break. I’m wondering if I can make a simple HF transceiver capable of working any HF band by driving a Pixie II CW transceiver with a SI 570 digital programmable oscillator.

Here’s what my pixie II sounds like on 80m.mp3 and 40m.mp3 with a strong antenna.

Preliminary work demonstrates a functional receiver powered by a crystal. I don’t think the currently-configured digital oscillator is putting out enough power to run the circuit, but it’ll take more time to get that up and running. For now, here are some photos of what I’ve got working and real sound clips of the thing are below. I’m happy with the case I built it in (thanks Ron!), and happy with my level drilling of the holes for power, output, and the CW key!

Briefly, the device is powered by a 9V battery. It’s hooked up to an 80m dipole antenna. Output is fed into a computer sound card for amplification / PSK31 analysis.

The internals reveal that it’s a simple circuit powered by a single crystal. More crystals are tucked in the case, stuck in foam, for easy transport.

Decoding of PSK31 is happening here, using output from my circuit with the 40m crystal in it.


Dental School is Boring

Summary: A student in their first semester of dental school had a rocky start but has since improved their grades and found a supportive study group. They have also discovered a passion for programming and amateur radio, but find dental school to be dull and unengaging. Despite this, they are holding onto their side interests to maintain their sanity.
This summary was generated in 64.14 seconds from an original post containing 191 words.

Mental Viscosity

Summary: The author of the blog post is expressing frustration with their studies and lack of creativity in their field of dentistry, and they plan to focus on their hobbies instead until they have more control over their studies.
This summary was generated in 57.42 seconds from an original post containing 313 words.

Wrapping-Up the Summer

Summary: The author has been working on several projects over the summer, including a microcontroller-powered prime number generator, a SQL HTTP hit logger, two scientific manuscripts for publication, and a DIY ECG project that was featured on HackADay.com.
This summary was generated in 83.79 seconds from an original post containing 205 words.