The personal website of Scott W Harden
⚠️ Warning: This article is obsolete.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.

Soup Can MEPT

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 Soup-Can Transmitter

The Signal

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

⚠️ Warning: This article is obsolete.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.

Measure QRP Radio Output Power with an Oscilloscope

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

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!

⚠️ 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.

AJ4VD Gator Spotted in MA

That's over 1,00 miles on a few milliwatts! The transmitter is the ridiculously simple one pictured below. I'm blown away! It was seen on running QRSS VD software! Awesome!!

AJ4VD Gator Chomps its way into Belgium!

Yeah, that's over 4,500 miles away! The following image was captured from ON5EX's QRSS grabber in Belgium! Amazing. I don't have the equipment to measure its power output, but it's running on USB power and I'd assume it's putting out less than 100mW. Very cool!

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