The personal website of Scott W Harden

MEPT Insulation Improves Stability

While it may not be perfect, it's a whole lot better. Below is a capture from this morning of my signal (the waves near the bottom). Compare that to how it was before and you should notice a dramatic improvement! The MEPT is inside a metal box inside a 1-inch-thick Styrofoam box. Very cool!

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

My oscilloscope decided to die on my right as I finally was able to view my 10 MHz waveform. I used a piece of coax with a load at the connector to the o-scope, and ran the coax to my test points. It was beautiful! ... and lasted about 30 seconds. The culprit seems to be a failing "focus" knob. My images had been getting blurrier by the day, and now it's completely black unless I twist pretty hard on the focus knob. I'd stick a small pot in there, but I have no idea how much voltage/current is being regulated. I'm sure the schematics are posted somewhere, but for now I'm going to try to clean out the potentiometer manually and see if the situation improves. Here are some photos of the circuitry inside this old scope. They don't make stuff like this anymore!

Update: I never got this scope to work again!

This article's source was last edited on September 10, 2020.
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QRSS Receiver Works... Barely

I completed work on my first RF receiver, and for what it is it seems to work decently. It should be self-explanatory from the photos. It's based around an SA602. As with everything, I don't plan on posting schematics until the project is complete because I don't want people re-creating junky circuits! It's stationed at the University of Florida's club station W4DFU and its spectrograph can be viewed in real time from the QRSS VD - Web Grabber - W4DFU page.

This article's source was last edited on September 10, 2020.
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⚠️ Warning: This article is obsolete.
Articles typically receive this designation when the technology they describe is no longer relevant, code provided is later deemed to be of poor quality, or the topics discussed are better presented in future articles. Articles like this are retained for the sake of preservation, but their content should be critically assessed.

Minimalist Radio Receiver

Now that my minimalist QRSS transmitter is mostly functional, I'm shifting gears toward building a minimalist receiver. These are some early tests, but I'm amazed I managed to hack something together that actually works! Once it's finished I'll post schematics. For now, here are some photos. This receiver is based upon an SA602 and although there *IS* an op-amp on the board, I actually bypassed it completely! The SA602 seems to put out enough juice to make my PC microphone jack happy, and those cheap op-amps are noisy anyway, so awesome! Go minimalism!

Here's the output from 7.040 MHz. Conditions are pretty bad right now, and I'm at my apartment using my crazy indoor antenna

This article's source was last edited on September 10, 2020.
Have something to say about this article? Let me know!
⚠️ Warning: This article is obsolete.
Articles typically receive this designation when the technology they describe is no longer relevant, code provided is later deemed to be of poor quality, or the topics discussed are better presented in future articles. Articles like this are retained for the sake of preservation, but their content should be critically assessed.

QRSS VD Image Assembler

This minimal Python script will convert a directory filled with tiny image captures such as this into gorgeous montages as seen below! I whipped-up this script tonight because I wanted to assess the regularity of my transmitter's embarrassing drift. I hope you find it useful.

import os
from PIL import Image

x1,y1,x2,y2=[0,0,800,534] #crop from (x,y) 0,0 to 800x534
squish=10 #how much to squish it horizontally

### LOAD LIST OF FILES ###
workwith=[]
for fname in os.listdir('./'):
    if ".jpg" in fname and not "assembled" in fname:
        workwith.append(fname)
workwith.sort()

### MAKE NEW IMAGE ###
im=Image.new("RGB",(x2*len(workwith),y2))
for i in range(len(workwith)):
    print "Loading",workwith[i]
    im2=Image.open(workwith[i])
    im2=im2.crop((x1,y1,x2,y2))
    im.paste(im2,(i*x2,0))
print "saving BIG image"
im.save("assembled.jpg")
print "saving SQUISHED image"
im=im.resize((im.size[0]/10,im.size[1]),Image.ANTIALIAS)
im.save("assembled-squished.jpg")
print "DONE"

Script to download every image linked to from a webpage:

import urllib2
import os

suckFrom="http://w1bw.org/grabber/archive/2010-06-08/"

f=urllib2.urlopen(suckFrom)
s=f.read().split("'")
f.close()
download=[]

for line in s:
    if ".jpg" in line and not line in download and not "thumb" in line:
        download.append(line)

for url in download:
    fname = url.split("/")[-1].replace(":","-")
    if fname in os.listdir('./'):
        print "I already downloaded",fname
    else:
        print "downloading",fname
        output=open(fname,'wb')
        output.write(urllib2.urlopen(url).read())
        output.close()
This article's source was last edited on September 10, 2020.
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