Wednesday, November 5, 2008

Getting Started on the RockMite

I started building up the RockMite 20 m CW transceiver yesterday. This is a great little kit and a great little project. I've been working in the logic design industry for the last fourteen years on projects like the Pentium, and the K5 and K6 processors. My part of these projects was done completely in simulation. Consequently, I haven't built a real board project in all that time. So, even though I suppose it should seem commonplace to me, I'm floored that for about $25 you can get a radio with an integrated receiver, transmitter, and a micro-controller that all fits on a board that's maybe 3" x 2"!

The first component I installed was the NXP SA612A double balanced mixer and oscillator shown below. Here's the datasheet for this little guy [pdf]. It's used in the receiver section to strip the carrier from the received RF signal leaving only the audio to be amplified and sent to the headphones. You can read more about the heterodyne and demodulation processes the device uses to do this at Wikipedia.

The chip package shown above is about a quarter inch long. Since I don't have a large magnifier in my workshop yet, I realized that a digital camera also makes a pretty effective tool for checking solder joint quality and for looking for solder bridges. It's not as fast as a good old analog magnifier, but it does OK in a fix.

The kit instructions do a great job of identifying which components should be used where. However, I was dismayed to discover that even though I didn't need to, I'd forgotten how to read capacitor values in the last fourteen years. I finally worked it back out. The capacitor above is read as 10 picofarads with four additional zeros tacked on the end which makes it 100,000 pF, or 0.1 microfarads. While hunting around for the answer to this mystery, I came across another great resource on the web: The Passive Electronic Component Handbook at Google Books. This book has more information than most folks will ever need on not only the use of passive devices, but their design and construction as well. If you're into that sort of thing, it's fascinating! Even though the web site said I was 'previewing' the book, I seemed to be able to go to whichever page I pleased.

KE7FEG just sent me a link to this great resource: "The Handyman's Guide to Capacitors"[pdf]. It's a five page guide to capacitors with the value codes I was struggling with annotated on the last page. The guide was written by NA5N and first appeared in QRP Homebrewer.

Well, it's back to work over here.


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