2nd Place Winner:
RF NimbleSig Generator, Thomas M. Alldread, Canada

Download the full project abstract

Our 2nd Place winner Thomas Alldread brings us NimbleSig an Enhanced Agility RF Signal Generator - Power Meter. He began his contest project with the simple assumption that "Virtually every electronics work bench should have a stable variable frequency RF signal generator that can be either analog or digitally modulated." Mr. Alldread has been working with DDS technology for use as digitally controlled, stable signal sources for over a decade.

Most of us are familiar with this type of 8-bit battle story. In his report Mr. Alldread says, "Due to the computational limitations of eight bit microcontrollers 'decimal digit - binary weight' lookup tables were used in the firmware for determining the new binary 32 bit DDS frequency tuning word (FTW) needed to update the DDS for each frequency change. The firmware for the eight bit controllers was rather tediously written in assembler language. This meant learning a new instruction set and more or less starting from scratch to write the code for each new controller platform utilized as technology evolved. Even with the high speed associated with firmware written in assembler language the eight bit controllers could not nearly match the maximum synchronous serial port data transfer rate of the DDS integrated circuits...This data rate bottleneck severely limited the modulation bandwidth possibilities which in turn limited the range of applications that my previous DDS based signal generators could be used for." He goes on to comment, "In consideration of all the potential benefits obtainable by using one of LMI's Stellaris ARM controllers I became motivated to build yet one more DDS based RF generator to add to my collection."

The NimbleSig project highlights the advantages developers find when working with the Cortex-M3’s 32-bit architecture. According to Mr. Alldread all the extra memory space "paves the road for a friendly user-interface". Definitely something that is also long overdue on every electronics workbench.

Project Details

This project is based on either AD9859 or AD9951 DDS integrated circuits from Analog Devices Inc. The DDS is controlled by an LM3S811, 50 MHz, 32 bit Stellaris Cortex M3 Core ARM microcontroller from Luminary Microcontroller Inc. running firmware compiled with Keil Software's RealView ARM C compiler. The project shows that the attributes of the Stellaris LM3S811 microcontroller make it an ideal choice for full bandwidth control of the low cost DDS integrated circuit alternatives used here.

This project describes a compact DDS generator / RF power meter module that provides a frequency agile RF output signal source with 1 Hz step resolution from below the VLF to the mid VHF spectrum segments (25KHz to 160 MHz). Additionally the capability of low level (-50 to +10 dBm) RF power measurement has been built into this module to complement its signal generation capability. This module, dubbed NimbleSig, has been designed with versatility in mind. It can either be keyboard controlled from a conventional PC running a simple terminal program or alternately controlled by a host microcontroller as dictated by the application.