# SWHarden.com

The personal website of Scott W Harden

# New Transmitter, New Spots!

``` qrss``` ``` amateur radio```

These should speak for themselves. Which signal is mine? Obviously I’m the crazy person who thinks it’s funny to merge molecular biology with amateur radio.

### Germany DL4MGM

``` microcontroller``` ``` circuit``` ``` qrss``` ``` obsolete```

I’m still working on this project, and although progress is slow I’m learning a lot and the circuit is getting better with time. I’m still not yet ready to post the schematics, but you can get an idea of what’s going on from the picture. It can handle 255 levels of frequency shift and has the ability to turn the tone on and off. 6 capacitors, 3 resistors, 4 transistors, a single inductor, and a micro-controller.

UPDATE I spotted myself on W4BHK’s Grabber about 300 miles away…

``````#include <avr /io.h>
#include <util /delay.h>

char dotlen = 5;                              // ultimately the speeed of transmission
char call[] = {0, 1, 1, 1, 2, 0, 2, 1, 1, 0}; // 0 for space, 1 for dit, 2 for dah

void setfor(char freq, char ticks)
{
OCR1A = freq;
while (ticks > 0)
{
sleep();
ticks--;
}
}

void sleep()
{
for (char i = 0; i < dotlen; i++)
{
_delay_loop_2(65000);
}
}

void slideto(char freq, char ticks)
{
freq = freq + 30;
char step = 1;
if (OCR1A > freq)
{
step = -1;
}
while (OCR1A != freq)
{
OCR1A += step;
setfor(OCR1A, 1);
}
setfor(freq, ticks);
}

void DNA()
{
char a[] = {4, 5, 5, 6, 6, 6, 7, 7, 7, 7, 8, 8, 8, 8, 8, 7, 7, 7, 7, 6, 6, 6, 5, 5, 4, 3, 3, 2, 2, 2, 1, 1, 1, 1, 0, 0, 0, 0, 0, 1, 1, 1, 1, 2, 2, 2, 3, 3};
char b[] = {1, 1, 1, 1, 2, 2, 2, 3, 3, 4, 5, 5, 6, 6, 6, 7, 7, 7, 7, 8, 8, 8, 8, 8, 7, 7, 7, 7, 6, 6, 6, 5, 5, 4, 3, 3, 2, 2, 2, 1, 1, 1, 1, 0, 0, 0, 0, 0};
for (char i = 0; i < sizeof(a); i++)
{
//slideto(a[i]*4,2);
//slideto(b[i]*4,2);
setfor(a[i] * 2 + 5, 10);
setfor(b[i] * 2 + 5, 10);
}
}

void ID()
{
for (char i = 0; i < sizeof(call); i++)
{
setfor(10, 50);
if (call[i] == 0)
{
setfor(10, 100);
}
if (call[i] == 1)
{
setfor(15, 100);
}
if (call[i] == 2)
{
setfor(15, 250);
}
setfor(10, 50);
}
}

void ID2()
{
for (char i = 0; i < sizeof(call); i++)
{
if (call[i] == 0)
{
ampOFF();
setfor(10, 50);
}
if (call[i] == 1)
{
ampON();
setfor(10, 100);
}
if (call[i] == 2)
{
ampON();
setfor(13, 100);
}
ampOFF();
setfor(OCR1A, 30);
}
ampON();
}

void ampON()
{
PORTA |= (1 << PA7);
PORTA |= (1 << PA0);
PORTA &= ~(1 << PA1);
_delay_loop_2(10000);
}
void ampOFF()
{
PORTA &= ~(1 << PA7);
PORTA |= (1 << PA1);
PORTA &= ~(1 << PA0);
_delay_loop_2(10000);
}

int main(void)
{
DDRA = 255;
OCR1A = 75;
TCCR1A = 0x81;
TCCR1B = 1;
while (1)
{
ID2();
ID();
for (char i = 0; i < 3; i++)
{
DNA();
}
}
}
``````

# Soup Can MEPT

``` qrss``` ``` amateur radio``` ``` circuit``` ``` obsolete```

This page documents the progress of my MEPT (manned experimental propagation transmitter) endeavors. If you have questions, feel free to E-mail me! My contact information can be found by clicking the link on the right navigation menu.

## The Spots

### Florida

288.3 miles away (W4HBK) May 22, 2010

### Massachusetts

1,075.5 miles away (W1BW) May 27, 2010

### Belgium

4,496.3 miles away (ON5EX) May 27, 2010

### Germany

4,869.2 miles away (DL4MGM) May 28, 2010

### Essex

4,356.4 miles away (G6AVK) May 28, 2010

### New Zealand

8,077.6 miles away (ZL2IK) May 29, 2010

# Measuring QRP Radio Output Power with an Oscilloscope

``` amateur radio``` ``` circuit``` ``` obsolete```

I added a backlight to my oscilloscope! My o-scope’s backlight hasn’t worked since I got it (for \$10), so I soldered-up a row of 9 orange LEDs (I had them in a big bag) and hooked them directly up to a 3v wall wart. In retrospect I wish I had a bunch of blue LEDs… but for now I can’t get over how well this worked! Compare it to the images a few posts back - you can really see the grid lines now!

I know this is super-basic stuff for a lot of you all, but I haven’t found a place online which CLEARLY documents this process, so I figured I’d toss-up a no-nonsense post which documents how I calculate the power output (in watts) of my QRP devices (i.e., QRSS MEPT) using an oscilloscope.

I think I have increased power output because I’m now powering my 74HC240 from this power supply (5v, 200A) rather than USB power (which still powers the microcontroller). Let’s see!

There’s the signal, and I haven’t calibrated the grid squares (this thing shifts wildly) so I have to measure PPV (peak-to-peak voltage) in “squares”. The PPV of this is about 5.3 squares.

I now use a function generator to create square waves at a convenient height. Using the same oscilloscope settings, I noticed that 10v square waves are about 7 squares high. My function generator isn’t extremely accurate as you can see (very fuzzy) but this is a good approximation. I now know that my signal is 5.3/7*10 volts. The rest of the math is pictured here:

140mW - cool! It’s not huge… but it’s pretty good for what it is (a 2-chip transmitter). I’d like to take it up to a full watt… we’ll see how it goes. My 74HC240 is totally mutilated. I accidentally broke off one of the legs, couldn’t solder to it anymore, and thought I destroyed the chip. After getting distraught about a \$0.51 component, I ripped ALL the legs off. Later I realized I was running out of these chips, and decided to try to revive it. I used a Dremel with an extremely small bit (similar to a quarter-round burr in dentistry) and drilled into the black casing of the microchip just above the metal contacts, allowing me enough surface area for solder to adhere to. I’m amazed it works! Now, to get more milliwatts and perhaps even watts…

# AJ4VD Gator Spotted in Essex, England

``` qrss```

It’s so awesome that such a small device can send such a low power signal so far away! Anyhow, the title says it all. Special thanks to G6AVK’s “part time” grabber for capturing this awesome series. That’s a 4356.4 mile trip on USB power! ha!