Search results

PA3FWM's software defined radio (SDR) page documents his extensive hardware and software development efforts between 2004 and 2009. Initial experiments utilized a direct conversion receiver with 90-degree phase difference, feeding a PC soundcard at 48 kHz sample rate, covering 24 kHz of spectrum around a 7080.5 kHz local oscillator. This setup, similar to AC50G's QEX 2002 article, allowed for basic I/Q signal processing to distinguish signals above and below the LO frequency. Limitations included fixed crystal frequencies, 16-bit dynamic range, and narrow bandwidth. Subsequent hardware iterations aimed for enhanced performance, incorporating external 24-bit ADCs with 192 kHz sample rates, connected via 10 Mbit/s Ethernet. A **MC145170-based PLL** and programmable octave divider provided a 58 kHz to 30 MHz tuning range. The **Tayloe mixer** was employed, with differential outputs feeding a PCM1804 ADC. An ATmega32 microcontroller handled serial data conversion to Ethernet frames, though without CRC calculation due to processing constraints. Later designs integrated AD7760 2.5 Msamples/second ADCs and a Xilinx Spartan-3 FPGA, enabling direct reception of 0-1 MHz spectrum and eventually 2.5 MHz bandwidth across the shortwave spectrum. Software was refactored to use an initial 8192 non-windowed FFT for efficient high-bandwidth processing. The project culminated in a two-way QSO on 21 MHz using the developed hardware and software, demonstrating transmit capabilities with a D/A converter. The system exhibited a 2.5 MHz wide spectrum display and a zoomed 19 kHz display, capturing signals like ionospheric chirp sounders and RTTY contest activity. Challenges included noise leakage from digital circuitry and cooling for high-power dissipation components.

Roger, G3XBM, shares his extensive experience in **QRP** (low-power) amateur radio operation, detailing various aspects of transmitting with minimal power. The resource provides insights into VLF (Very Low Frequency) reception techniques and the construction of simple **crystal radio sets**, reflecting a foundational approach to radio experimentation. It includes links to external resources covering QRP clubs, online receivers, manufacturers, and technical references, offering a curated collection for enthusiasts. His page serves as a hub for those interested in the challenges and rewards of QRP, often comparing the efficacy of different low-power setups. The practical application extends to understanding basic radio principles through hands-on projects like crystal sets, which G3XBM has explored. The collected links provide a starting point for further research into specific QRP equipment or operating practices, drawing on G3XBM's long-standing engagement with the QRP community.

The Rock-Mite is a 40m CW kit offered by Small Wonder Labs . It features built-in keyer, direct conversion receiver with a crystal RF bandpass filter, 500 milliwatts of power, and switchable frequency offsets to work around QRM

Crystal receivers, construction projects and plans, old-time crystal sets, hints, crystal receiver store.