Modular Homebrewing for Amateur Radio

Introduction

Having discovered the concept of the DDS VFO, my good friend Mark, KD5AMB, and I began to consider the possibilities of using one at the heart of a homebrew station. Some of the work of making such a station multi-band would already be done, since the DDS VFO could generate RF signals throughout the HF spectrum. A lot of simple homebrew circuits could be fed a signal from a DDS VFO either instead of a crystal, or in a circuit designed with a VFO in mind. Some of them, such as a simple direct conversion (DC) receiver, could cover wide areas of spectrum this way. Separate pieces of equipment, some pre-existing, and some built for the purpose, could (with the help of some T/R switching, etc.) work together effectively with each being fed its operating frequency from the same VFO.

Using a DDS would require devising some sort of computer control over its output frequency. The same control computer could also be used for T/R, keying, and any sort of bandswitching that needed to be done, as well as provide frequency control options such as memories, T/R offset, and RIT. Computer control could be through the parallel port of just about any old computer, or through a PIC chip.

The more we talked about this project, the more we began to realize that we were talking more about a philosophy of interconnecting radio building blocks than just a project about a VFO. In fact, our philosophy could be employed using a crystal oscillator, a toggle switch to handle T/R, a straight key for keying, a direct conversion receiver, and a simple RF output amplifier. Although limited to a single frequency, the resulting system would be a reasonably well functioning transceiver. Throw in the DDS VFO and its computer control requirement, including the ability to provide features such as T/R offset and bandswitching control, and the transceiver could now function more adequately, and (depending on the RF output amplifier's frequency range) do so on a variety of HF bands. The various modules could be built and upgraded one by one, and upon completion, each module could be put to use with the rest of the station, right away. Designers could design individual modules using a known interface, and everyone's designs could be used together. We've decided that we'll focus on defining this interface philosophy and designing some of the basic building blocks, then see if others are interested in helping the idea grow. We believe it will be a satisfying, efficient, and effective approach to homebrewing.