Preface

The purpose of this web-document initially was to share the progress made in evaluating and further improving the well known H-Mode mixer circuit invented by G3SBI.

Since then I have received much feedback, encouragement and help! Because of this and the excellent results possible with the H-Mode mixer, I have expanded the scope of this web-document now to report on the progress made with the development of a complete high-end HF-frontend. This frontend is 100% based on the successful and well known CDG2000 frontend and should be seen as an improved version of an already great design.

The roots of the CDG2000 frontend probably go back to the early sixties of the previous century. The SS-1R receiver developed by Squires and Sanders is seen by many as the first receiver to obtain good dynamic range by eliminating any gain stages before the first crystal filter. Shortly after that, Bill Squires, W2PUL and his companion, perished in an aircraft accident, and had no chance to further improve the concept.

Nowadays much attention in HF-receiver development understandably goes to DDC (Direct Digital Conversion) and SDR (Software Defined Radio). However the dynamic range possible with a classic "no gain before the roofing filter" analog "H-Mode" frontend is so good that it probably will remain successful for quite some time to come in high-end HF receivers. A combination of the two technologies will most likely be the optimum in practical receiver design before DDC is mature and sampling directly at the antenna takes over completely.

Acknowledgments

First I would like to thank Colin Horrabin, G3SBI. Without his support, advise and ideas this document would not have been possible. I would also like to thank Mark Sumner and AOR-UK for supplying many of the different components needed in the H-Mode mixer evaluation. Many thanks go to Helmut Dick, EA5GNI, for making the ultimate +53dBm roofing filter possible! My thanks go to Harold E. Johnson, W4ZCB and Bill Carver, W7AAZ for their constructive feedback and encouragement during this project.

I would also like to thank Giancarlo Moda, I7SWX, for his contribution to the 2-transformer mixer testing, by supplying the transformers and also a complete mixer assembly.

Last but not least I would like to thank Helmut Singer, Dirk Steinmeier and the crew of Helmut Singer Elektronik for their constructive support with my refurbished SNA62 spectrum/network analyzer, without which I would not have been able to quantify many of the frontends characteristics.

Any ideas and suggestions to further improve the frontend or especially the H-Mode mixer are very welcome. I intend to keep this web-document up to date as new ideas or better components arrive! I can be contacted at:

73's
Martein
PA3AKE

Februari 2008

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