RF Hacking

The idea is simple: build a low-cost, purpose-built HF receiver around a cheap high-speed ADC instead of repurposing an RTL-SDR. An RTL-SDR is an excellent general-purpose radio tool, but it was not designed as a high-dynamic-range HF receiver. A direct-sampling design with proper HF preselection, controlled gain, a stable sampling clock and FPGA-based digital down-conversion should make a more interesting homebrew receiver. The goal is not to claim IC-7300-class performance from a $25 design. The goal is to explore the same broad receiver architecture at a much lower cost and to measure honestly how well it works. ...

This is an early design sketch of VHF (2m - 145 MHz) APRS beacons that are small and can be placed in vehicles like ambulances or fire trucks. Key Points Si5351 module powered by the usual 25 or 26 MHz 0.5 ppm TCXO. Si5351 generates 145 MHz Two-Tone APRS RF output directly! Using an Si5351 for APRS (Automatic Packet Reporting System) transmission via FSK (Frequency Shift Keying) allows us to generate highly accurate AX.25 packets directly at the RF frequency (e.g., 144.390 MHz), eliminating the need for a separate modulator and VCO.Since APRS typically uses AFSK (Audio Frequency Shift Keying) fed into an FM transmitter, generating FSK with an Si5351 means directly shifting the carrier frequency or the VFO instead of modulating an audio tone. ...

This is an early design sketch of a UHF (70cm - 440 MHz) WSPR beacon. This design comes from Ismo (OH2FTG). Key Points 10 MHz OCXO TCXO powering the Si5351 module instead of the usual 25 or 26 MHz 0.5 ppm TCXO. Si5351 generates 217 MHz output, which we double to ~434Mhz using the https://techlib.com/files/diodedbl.pdf technique. Use 440 MHz SAW filter at the output (from LCSC) ONSEMI MMBD701LT1G RF Schottky diodes - locally available ...

I learned about the Sub-1€ TRX challenge from Ismo (OH2FTG) - thank you (maybe for getting me addicted?). The constraints Sub-1€ TRX, with LCSC parts. This excludes the PCB, so it can be 10x10 2-layer or 5x5 4-layer. My Design WIRELESS WL4456 (TX) and WIRELESS WL550 (RX) pair - 17 cents T/R switch: TECH PUBLIC TPAS169-73LF - 16 cents 13.56 MHz crystals (HY13560M49SBSMDOB1R30 / 8DSC135G0012L) - 5 cents * 2 MCU: PY32F002AL15S6TU SOP-8 from Puya - ~11 cents ...

The constraints 5V (~500mA) power from mobile phone 1W RF output required Very compact with less "moving" parts 14 MHz capable The design We use INNOTION YG401530VB MMIC in this design. 100n Si5351 CLK 0 --||----+---------+ | MMIC | | IN | | | | OUT +----||---- RF OUT ---- LPF ---- 50R dummy load +----+----+ 100nF | 10uH RFC | |---100n---GND | +5V Note: No explicit 'special' matching required it seems ;) This seems to be an extremely broadband circuit which should cover all HF! Results 10 dBm from Si5351 and 13.8 dB gain of the INNOTION MMIC gives ~9.8Vpp output theoretically. ...

The constraints 5V (~500mA) power from phone 1W RF output required Very compact with less "moving" parts 14 MHz capable The design We purposefully utilize "high Rds" EPC GaN parts with very low Qgs. Simulation Results Power consumption: Around 300mA @ 5V. pout: AVG(v(out)*i(r3))=1.0606 FROM 5e-05 TO 0.0001 pin: AVG(-5*i(v3))=1.38209 FROM 5e-05 TO 0.0001 isupply: AVG(-i(v3))=0.276418 FROM 5e-05 TO 0.0001 eff: pout/pin*100=76.7393 Cost Cost: < 500 INR. ...

Related work Baby QRO Switching RF amplifier for HF Digitally Adjustable RF PA Supply A new generation of the Baby-QRO switching amplifier targets 25W to 50W of RF output for FT8 and other FSK modes. While it can do 100W, it becomes more of a thermal engineering project then ;) It is designed to operate with a Bare DDX-Commercial transceiver board and has an inbuilt T/R switch. Design 3D render: ...

I could NOT get the Open-Source Thermal Simulation of PCBs technique to work with my 4-layer PCB board at all, even after spending some days on it. To make things worse, I was NOT able to get useful debugging feedback from the involved patchy toolchain. Getting access to the TRM software by ADAM Research turned out to be a sort of very bureaucratic and slow process - I never ended up using it. ...

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 ...