RF

Polar Modulation for Everyone We have been working on SSB generation using polar modulation. Hardware stack: RP2350-Zero MCU board + Fast Si5351 module + AP63301 buck regulator (for 5W mode). See https://github.com/kholia/PolarModulationSSB for details. Audio fidelity is acceptable at the moment and should improve further. We still need to hook up the amplitude ("envelope") restoration stage. Motivation Why should Guido, Hans, and FlexRadio folks have all the fun? ;) ...

I recently worked on a redesign of the PA0FRI active antenna using high-speed BFR93A, BFR106, and BFR193 transistors. As a fallback in case of issues, we planned to use NXP MMBT2222A,215 transistors. Design 3D render: Schematic: Previous Next     / [pdf] View the PDF file here. Simulation Results ...

Idea Ismo recently shared the https://github.com/CoolNamesAllTaken/adsbee project, which is very interesting. Challenges The ADS-B (Automatic Dependent Surveillance-Broadcast) system uses a data rate of 1 Mbit/s (1 megabit per second) for aircraft position and identification transmissions on 1090 MHz. Unfortunately, this is too fast for HOPERF CMT2300A and related transceiver chips. This led us to consider the following VFM ADS-B RX chain. Architecture Here is a simple ADS-B receiver chain. Antenna (a simple dipole / ground-plane antenna / PCB antenna) ➔ Zeenko LNA ➔ ADS-B Bandpass SAW Filter ➔ 100 pF (DC block) ➔ (Optional digitally controlled RF attenuator for AGC loop) ➔ Fast Schottky detector diode (BAT68 SOT-23) ➔ RC filter (10 kΩ, 10-33 pF) ➔ MCP6567 SOIC-8 comparator with output pull-up ➔ MCU GPIO (RP2350 PIO controlled). ...

The HFDY Active Loop is working extremely well, even from an indoor location in MK68. Design I am currently running the loop at 5V (via a regulated linear power supply), where it consumes slightly less than 65mA. The recommended voltage is 10V, which I plan to switch to soon. Results I am using Airspy HF+ Discovery SDR for this experiment. Future work It would be very interesting to compare this HFDY Active Loop against the PA0FRI Active Antenna. ...

My homebrewed PA0FRI Active Antenna is working well from a very physically constrained location. Design 3D render: Schematic: Results The antenna is connected to an RSP1 Clone SDR running custom FT8 band-hopping software. I am using a SOLID 4-Way 5-2400 MHz RF splitter to connect multiple SDRs to the same active antenna. NB: Plug in 75-ohm dummy loads (terminators) on the unused splitter ports; MX-282 / MX-280 75-ohm loads work fine. ...

Sometimes we all need a bit of QRO - Life's too short for QRP sometimes. So we give you the Baby-QRO switching amplifier! This Baby-QRO switching RF amplifier design is inspired by the wonderful Single NXP MRF-101 Eval Board project by Jim Veatch. Thank you Jim! Instead of using the expensive MRF101 MOSFET, we use fast SiC MOSFET(s) from Wolfspeed / SUPSiC. Design 3D render: Actual picture: ...