An Integrated and Portable PSK Station for 80 & 20 ... without using a PC!
Color photos, schematic and diagrams for an article written by N2APB for Fall 2000 QRPp. Also the subject of a presentation made at the Pacificon QRP Forum in October 2000.
PSK31 is the latest communications mode to sweep the interest of hams worldwide. Its inherent ability to dig out low, near-inaudible signals from the spectrum is ideally suited for low power QRP enthusiasts. But today’s technology is tied to use of a portable computer, or even to a desktop computer. Thus the PSK operator is locked into a cumbersome and often fixed-location station. But there’s hope!
Here I present the design and construction of a two-band PSK station utilizing a small and inexpensive DSP controller board coupled with the simple PSK transceiver boards from NN1G and Small Wonder Labs. I detail the techniques used to perform PSK processing in a small form factor, and the techniques used to create a novel and very functional "human interface" using a keyer paddle for input and audio Morse for output ... to create a PSK rig that can be easily taken to the field.
Front view ... The rig is shown here in QSO with NN1G, with tuning indicators showing a PSK tuned condition state.
Rear view ... Notice the plethora of connectors, providing optional interconnect to an IBM keyboard, external transceiver, and serial port for external logging and/or control. Internal battery battery can be selected as the power source instead of the external power supply.
Internal - layer 1 ... Construction was quite cramped and it was necessary to put three levels (or layers) of circuit boards into the blank K2 box (from Elecraft). Shown here is the bottom-most layer 1 with the two NN1G PSK-xx transceiver boards.
Internal - layer 2 ... The middle layer contains the 56KEVM DSP evaluation board used as the PSK modem. The software for this is a slightly modified version of the original PSK31 source code from Peter Martinez, G3PLX, the father of PSK31. (Peter provided some guidance in this project, for which I am very grateful. Same too for some great help from Doug Braun, NA1DB).
Internal - layer 3 ... The top layer contains the I/O controllers (also called the "supervisory controllers"). The board on the right is an inexpensive off the shelf microcontroller that lends itself nicely to C programming, and the (incomplete at the photo time) board on the left is the custom 8051 microcontroller board. The next step of the project evolution is to merge these boards onto either one or the other. I'm not sure at the moment which would be the better direction to go, but from a cost perspective, I'll probably move everything onto the 8051 processor board. This will make ultimate reproduction by others a bit easier.
Simple Block Diagram ... This simple diagram shows the signal flow within the system. Simply stated, the RF signal comes into the PSK-xx boards, which deliver demodulated audio tones to the DSP modem board. The modem talks to the "spectral processor" board which deals with phase and frequency relationships from the raw modem data. The spectral processor board talks to the I/O controller board which contains the Morse-ASCII-Morse converters used for user input and output. The I/O Controller also deals with tuning and optional I/O (LCD, keyboard, external computer, etc).
Detailed Block Diagram ... A very specific system interconnect diagram, as an enhanced derivative of the Simple Block Diagram.
Tuning Display ... The dual LED bar graph arrays are used to indicate when a PSK station is tuned properly. (Software also automatically takes the rig to the "next station" and indicated this tuned condition of 2 mating LEDs being illuminated.)
I/O Controller Schematic ... The schematic of the 8051 microcontroller board.
MORE TO COME
This is all the information that will be placed onto the website at this time. Full details can be found in the 20 page article in QRPp magazine. The project continues to evolve and an update will be presented in the Winter issue of QRP Homebrewer magazine, and potentially in the ARRL's QST or QEX publications.