PIC-A-STAR: a Software Transmitter And Receiver

摘要

Software is this month's topic, namely an outline of what it does, how it works, how it is packaged and how you obtain it. Illustrated in Fig 2 is the functionality implemented in software. You will have seen not dissimilar block diagrams implemented in analogue hardware - but not at this price and not inside a 28mm~2 chip! Actually, there is an intrinsic overhead, namely that the analogue signals need converting to digital form before processing -and back to analogue after. This is the purpose of the CODEC (encoder/decoder) referenced on several inputs and outputs -and is implemented on a separate chip. The greatest appeal of the software approach, not least to the amateur, is the flexibility to change the line-up at a touch of the keyboard, so to speak. This allows easy experimentation (or overt tinkering, if you prefer), since at any time you can abandon the change and go back to the previous version. There are other subtleties. For example, you will find five 15kHz oscillators scattered around the diagram. In fact their frequencies change depending on mode ie USB / LSB / CW. In DSP software terms the sinusoidal oscillator is simply a subroutine. To invoke it, all you need do is tell it what frequency / phase you want on any given occasion - and it is done.