It all began with the nonavailability of expensive mixer ICs. I homebrewed my own mixer IC (parts shown in dotted square), and as I had already described it in my blog post of 9th February. Keen to having made the "PIXER" superhet receiver and other projects based on it...........finally I started to build a DSB rig around it but over the last couple of weeks, design evolved with a bit of tinkring here and there and ultimately it took shape of a very nice companian H.F. CW/SSB transmitter to "PIXER"; having a clean spectral purity and a a side band suppression of around 58 dB. Indeed great for a thing developed around common off the shelf components and right on your kitchen table......and all that with a home brewed X-tal filter!!! The schematic of the exciter unit is as under:
The circuit of PIXET exciter is quite simple in itself and requires no description. I have used components that were available on hand. Especially the transistors. You can substitute them with any general purpose medium power ones having adequate gain bandwidth product. Though matched pair of transistors has been used in the balanced mixer but R6 has been included for refining the circuit balance. It can be carefully adjusted for minimum carrier during no audio signal present at the microphone input. A simple diode gate provides the CW keying. Could there be anything simpler than that....? And that's the real essence of QRP home brewing.....!!!