Surface Mount QRP Transmitter

Here is a closeup of the first prototype.
Almost 3 of these can fit in an Altoids tin, leaving
plenty of room for a matching receiver.

Here is the QRP TX in a mini cinnamon tin.
This is the display I used for the SQRPion
hombrew contest.

Project Details

This is a prototype, to test a couple of ideas I wanted to try. The first was the idea of using a logic chip as a gated oscillator, the second was to see if a FET PA (aka 38 Special) could be done surface mount instead of the usual TO-220 IRF-510. This project was a success a number of ways, even though some of the ideas didn't pan out. First off, it was my first SMD QRP design and it mostly worked. And, everyone else that's seen it really gets a kick out of this tiny design. The idea of using a logic chip as an oscillator sorta works, but has a problem with pulling a bit off freq as the chip warms up. I could probably buffer it with a 2nd chip to minimize heating the die on the oscillator chip, but by the time I do all that I might as well make it from a few SOT transistors and be done with it (that will be Rev X2). The FET PA worked very well, this design puts out 5.25 watts with 12.5 volts on the drain. It's probably a little too much for the device, but the fact that it can do it and not burn up tells me there's plenty of overhead when set up to output 2 watts or so, which was my original design goal. So, the design presented here really isn't a "finished" project, but a "work in progress". The design is submitted solely for informational purposes only, if you build it, expect some problems.


Click on the icon to dowload a ZIP file of all the parts and printed circuit documentation required to build this project.

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