Steve Hicks and Greg Jurrens explain what went into designing the ultimate, easy-to-use ham radio and how advances in analog electronics made the difference.
On Malpelo Island, a barren spot off the coast of Columbia surrounded by hammerhead sharks, it’s not easy to connect with the rest of the world. Yet in January 2012, a team of radio amateurs set up camp, assembled their “shack” and made nearly 200,000 contacts with other ham operators around the globe.
In “radio contesting,” individuals and clubs compete to see how many ham stations they can reach. It can be an extreme sport. Organized “DX-peditions,” like the one to tiny Malpelo Island, involve travel to distant, sometimes dangerous places—maybe just a spot on the grid where no ham operator has gone before. It’s a test of survival and technical skills.
In some ways, our company’s evolution has been one long DX-pedition, as we’ve gone where no other ham radio company has gone before. When CEO Gerald Youngblood (K5SDR) sat down at his kitchen table a decade ago, he wanted to control his ham rig from his computer. Instead he turned his PC into a radio and helped put software-defined radio (SDR) on the map.
In 2002, FlexRadio Systems produced the world’s first SDR experimenter’s kit for amateurs. It was truly possible to receive an RF signal, convert it to a digital bit stream, and perform all of the modulation and demodulation of the signal with digital signal processing in the computer. The obvious difference over traditional radio? No knobs.
Today, advances in analog technology make it possible to offer amateurs a new class of radio once affordable only to commercial, government, and military users. Our FLEX-6000 Signature Series is a plug-and-play SDR that achieves direct digital reception, transmission, and networking – and as many as eight receivers at once on the RF spectrum. What that means on Malpelo Island, or for anyone working a contest, is more people can hammer their signal through at the same time. If there’s one thing ham operators hate, it’s being stuck in a pile-up.
Signal processing challenges
Creating the FLEX-6000 presented several major design hurdles. The biggest problem in SDR has always been how to traverse the analog and digital worlds at high enough rates and accuracy. So our number one challenge was finding an analog-to-digital converter (ADC) powerful enough yet affordable for amateurs. We found a possible solution while working on a project for a commercial client that required a more sophisticated, wide-band sampling receiver. Our HF radios have always used narrow-band technology. Did we dare dream of a wide-band model for hams?
After looking at dozens of options, we zoomed in on the Analog Devices Inc. AD9467, a 16-bit ADC that’s fast (245.76 Mega samples per second) and can be placed directly on the antenna without needing an external buffer amplifier (say goodbye to distortion). Direct digitization of the RF signal at the antenna connectionis a huge advantage. Basically, the faster and wider the sampling, the easier it is to weed out unwanted signals and enhance desirable ones.
When component problems cropped up, ADI application engineers helped us throughout the prototyping process. For example, working with the AD9467 ADC, we saw large spurs when we approached a multiple of our sampling frequency. ADI duplicated our setup in the lab, and, as we compared data, it became apparent that we had a scaling issue and the part was actually performing better than anticipated.
With our ADC nailed down, we built a direct wide-band sampling receiver that surpasses narrow-band for dynamic range, spur performance, and phase noise. Our transceivers and receivers allow for the creation of four to eight independent slice receivers with tuning from 0.03 MHz to 77 MHz and 135 MHz to 165 MHz. Direct RF to digital conversion delivers dynamic range just as high at 100 Hz spacing as it is at 2 kHz spacing. Since all the mixing and filtering of signals is done digitally, there’s no need for expensive filters and other parts. Direct digital receivers are a lot quieter.
We also located a good clock reference to ensure low phase noise. One problem with legacy multi-conversion radios is that the frequency synthesizers used for tuning are notorious for high close-in phase noise and spurious output. Our hardware architecture incorporates an ultra-low phase noise master oscillator operating at 983.04 MHz. Clock drivers, such as the AD9512 from ADI, deliver phase noise performance better than -130 dBc/Hz at 1 kHz offset, and -152 dBc/Hz at 100 kHz offset. Operators can hear weaker signals and transmit cleaner signals. Of course, transmission is also 100 percent digital. By embedding ADI’s high-performance A/D and D/A converters, our new product outperforms traditional radio on both transmit and receive.
We also needed to build in enough computing horsepower to take advantage of wide-band direct sampling. We found the XilinxVirtex®-6 field programmable gate array (FPGA) could perform all digital up and down conversion as well as spectral analysis. The XC6VLX75T / 130T FPGA does the amazing. The midrange FLEX-6500, for example, delivers 191 GigaMACS and 78 GigaFLOPS. Additionally, Xilinx FPGA platforms work well with ADI data converters