Monday, April 28, 2014

Building an SDR Kit Project: The Lil Pup build, by PARC Homebrew

One of the reasons why I was interested in the Ham Radio Hobby is because of the strong "homebrew" contingent within the hobby. I just like it when people will fire up their brains, and their soldering irons, and build stuff.  And I want to learn how to do that too.  A good step towards that goal is to start doing kit builds, and to practice and improve my soldering skills, along with my ability to read and understand some fairly simple circuit schematics, and test and diagnose problems if my build goes awry.

I signed up for a BuildAThon day with the Peel Amateur Radio Club (PARC), who are a really fun bunch of folks. I joined the PARC club, paid my dues, and signed up for a slot at the buildathon day. I obtained a soldering station, two actually, used, at a low price.  I bought all the items on the "suggested things to bring" list, and I showed up at the buildathon day.

I have to take a moment to express my gratitude to the wonderful folks who put this build together. Here is a quick list of the kind of jobs that go into this kind of build:

* Select a project that is interesting enough, but not too difficult for your group (They hit this one out of the park in my opinion: Build an HF SDR? How cool is that!)

* Obtain all the parts and put together the kits (This was done very very well)

* Write the documentation  (This part was done amazingly well)

* Obtain the necessary shared equipment, in this case, a reflow oven, a drill press, test equipment, and extra soldering stations.

This is all done by volunteers. This is why Amateur Radio Clubs are so great.  I'm so impressed by the HomeBrew group within the club, and with the PARC club all around. Well done, gentlemen, well done.

Anyways,  here's a picture of me, and a picture of My Thing Which I Built, and I Think Is Really Neat-O:

Here is a close up of the board, which is populated with surface mount coils, resistors, capacitors, one RF mixer IC, a 155 mhz oscillator, a voltage regulator, and a couple of diodes:

Underneath the board you can see is a small pre-made assembly which is the inside of an "RTL-SDR dongle", the 50 mhz to 1.2 ghz SDR "brains" of the operation. The green board on top is an upconverter that slides a segment of the RF spectrum from 1 to 80 mhz up to 125 mhz where the Realtek RTL-SDR chip can 'see' it.

The upconverter design is an open hardware design from, and the design was modified, and placed in a cool "Altoids tin" which, when closed up, makes a nice little enclosure.   I am a big fan of ersatz kit enclosures, whether they be mint tins, or tuna tins, or what have you.

I don't think I could have built this kind of kit, even if I purchased the board and the components in a big bag of stuff. I had a little trouble with the reflow, the oven didn't really get hot enough and there wasn't enough solder/paste on the right side of the board, so I needed a bit of help from a more experienced solderer to rework the right side of the board. You can see there is more solder over there because it was hand-soldered, whereas the left side seems to have reflowed properly.

This is big fun, people, I highly recommend kit building, especially "kit building as a team sport". This was a really fun day, and I am now highly motivated to go try building a few kits on my own time, now that I've had a taste of kit-building success.  The best part? My little radio works. There will be a post or two later when I've figured out enough software stuff to be able to show something new. I have some ideas, and since I'm a pretty able software developer, I think I might be able to do some nifty stuff with this little rig.

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