SDR Transforms Amateur Radio

OTHER SDR PRODUCTS
Most SDR products are receivers. The WiNRadio model WR-G303e generalcoverage shortwave receiver covers 9 kHz to 30 MHz (Fig. 6). This traditional dual-conversion superheterodyne offers IFs of 45 MHz and 12 kHz. DSP filters provide selectivity as narrow as 500 Hz for CW, 2500 Hz for voice, and 6 kHz for shortwave broadcast AM. Demodulation for AM, SSB (LSB, USB), CW, and FM is also DSP. The radio connects to the PC via a USB port. A software front panel provides the displays and controls.

Perseus offers an unusual SDR receiver that isn’t superheterodyne or direct-conversion. Instead, it’s a direct digital sampling receiver. After some frequency pre-selection at the antenna with LC bandpass filters, the signal goes to an LNA and then directly to a 14-bit, 80-Msample/s ADC that converts the entire band to digital. DSP implemented in a FPGA then does all of the filtering, demodulation, and tuning. It connects to the PC by a USB port. A software front panel implements the displays.

RF Space makes two SDR receivers. The SDR-IQ covers the 100-kHz to 30-MHz range. It features a 190-kHz bandwidth and a wide range of software demodulation methods. The SDR-14 has similar features but can also digitize spectrum from another receiver up to 130 MHz. Both of these receivers feature full-blown frequency-spectrum and waterfall display capability. They also use RF Space’s SpectraVue software, which runs on the required PC.

Designed by Tony Parks (KB9YIG) and Bill Tracey (KD5TFD), the SoftRock SDR receiver can be found on a small printed-circuit board (PCB) with a USB connector that plugs into a PC. It produces I and Q outputs that must go to a PC sound card for analog-to-digital and digital-to-analog conversion.

Similarly, Phil Covington (N8VB) developed the Quick Silver SDR receiver. This direct digital conversion device digitizes the antenna input with a Linear Technology LTC2208 ADC. The overall frequency coverage is 15 kHz to 55 kHz. An Altera Cyclone III FPGA handles the DSP and related functions. The GNU Radio project and its software also are worthy of investigation. Check their Web sites for details.

If you want to learn SDR, the ham radio community is a great place to start, whether or not you’re a ham. The available products make it possible to get up to speed quickly without the hundreds of hours typically needed to design hardware, write code, and run endless tests.