"Portable SDR"

A portable software defined radio

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The SDR-908 is a software defined radio designed specifically for portable use, without the bother of being tethered to a PC or soundcard for the modulation/demodulation processing performed in this kind of radio.  The SDR-908 uses a microcontroller and dual-DDS daughtercard for front panel frequency navigation and quadrature clock generation, and a DSP daughtercard for the signal processing needed to take the RF signal from IF to baseband audio. Of course, not all of the bells & whistles are present as when compared to a full SDR software application running on a PC, but the signal and frequency spectrum displayed on the text LCD (and later on a graphics LCD) certainly allow flexible, powerful and battery-operated SDR transceiver use in the field.

The SDR-908 project consists of two parts: a front panel mounted "digital control unit" and a shielded "RF unit" comprised of a QSD/QSE board, RF filters and a QRP linear amplifier.

   [Block Diagram]


The Digital Control Unit is an HC908 Daughtercard based design that uses an LCD, pushbutton and rotary encoder on the front side of the controller board, comprising the user interface.  The HC908 Daughtercard and the DSPx daughtercard are located ont he backside of the controller board.  Also on the backside is a socket for a DDS-60 daughtercard or Lyle's dual-DDS card thus allowing computer control of the I-Q phase relationship. 


The digital control unit inherits many of neat-and-proven features of the Micro908 software: VFO display and encoder-driven frequency navigation, RS232 serial port for control+DSP software updates, auto power-down timers, band-setting and scanning capabilities. The LCD is text-only for now, but there is a graphics display in the works in order to display frequency spectrum.  

The RF Unit is comprised of a QSD/QSE/RF module that resides in a shielded sub-enclosure inside the main SDR-908 case. The SoftRock v4 now serves as the sampling front end for the receiver. Soon the v5 design with its band modules (and soon thereafter with a mating transmitter module) will serve in place of the v4 hardware, thus serving as the transceiver RF unit. Alternatively, other QSD/QSE-based hardware designs may be used with the SDR-908.


Overall, the combination of the Digital Control Unit with SoftRock module(s) provide for a nice, band-changable, battery-friendly portable SDR transceiver.

Adjustng the Phase ...


The prototype receivers are working now and we'll soon be making about 20 units available in a trial. One will have to buy the pcb for the control unit, as well as the other parts that mentioned above, but they will all be "at cost" until the bugs are shaken out in order to have a full production kit run.  Should be fun.

73, George N2APB

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Page last updated:  November 17, 2005