Amateur Radio

We are working on reversing the Huidu HD-R712 LED Display Full Color Receiving Card - a very cost-effective (~1000 INR) and widely available FPGA board. We draw inspiration from the https://github.com/q3k/chubby75 work. FPGA Blink Project Files 1 Random brain dump $ sudo openFPGALoader --cable dirtyJtag --freq 10000 --detect Jtag frequency : requested 10000Hz -> real 10000Hz index 0: idcode 0x4014c35 manufacturer anlogic family eagle d20 model EG4D20EG176 irlength 8 $ sudo openFPGALoader --cable dirtyJtag --detect Jtag frequency : requested 6000000Hz -> real 6000000Hz index 0: idcode 0x4014c35 manufacturer anlogic family eagle d20 model EG4D20EG176 irlength 8 JTAG pinout: V ┌───────────────────┐ │ 1 3 5 7 9 │ │ 2 4 6 8 10 │ └───────────────────┘ 9 => TCK 7 => TDO 5 => TMS 3 => NC (Not Connected) 1 => TDI The pin mapping work was done using a DMM, the datasheet, and an optical magnifier. ...

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 ...

The PE4312 is a 50Ω, 6-bit RF digital step attenuator available for around 2 USD. Pretty neat for implementing real digital AGC! For half-the-price we can get the alternate Archiwave ARW637 or ARW621A ICs which work very similarly to PE4312! References: Archiwave ARW637 Archiwave ARW621A

This short article describes a flight-safe power supply for FieldOps. Component List Simply get these: USB QC/PD AFC trigger decoy board (9V) USB QC/PD AFC trigger decoy board (12V) USB QC/PD AFC trigger decoy board (15V) Xiaomi Pocket Power Bank Pro 10000 33W This one does 9V, 12V, 15V and 20V without any problems. OR A 65W USB PD power bank - not needed for 5 to 10W QRP FieldOps ...

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. ...

Setup: Si5351 RF generator (@ 28 MHz) ➔ GSD-Hacks-v5 digital amplifier ➔ 7th order LPF ➔ {COAX-UNDER-TEST} ➔ Digital RF power meter ➔ Dummy load Results Results at 13.8V drain: Coax Type Power Reading RG-58 (7 meters) 4.5W RG-316 (7 meters) 3.9W RG-188 (7 meters) 3.9W Results at 15V drain: Coax Type Power Reading RG-58 (7 meters) 5.4W RG-316 (7 meters) 4.7W RG-188 (7 meters) 4.7W These measurements appear to match those from Eric, WD8RIF. ...

Here is the schematic for a standard 50Ω LPF for the 12-11-10m bands. Designs PCB Render: Actual photo: Performance NanoVNA results of the PCB build: Build Notes These values come from RobG (https://hackaday.io/) Shunt C: 100pF Series L: 12T on T37-6 core, 11T on T50-6, making about 485nH Shunt C: 180pF Series L: 13T on T37-6 core, 12T on T50-6, making about 580nH Shunt C: 180pF Series L: 12T on T37-6 core, 11T on T50-6, making about 485nH Shunt C: 100pF Winding wire size: 27 SWG (is non-critical) Note: We needed to reduce 1T (from the values specified above) when using the T50-6 cores. As usual, use a DE-5000 LCR Meter (or better) to know the exact values. ...

Setup OS and SDR Please use the latest Raspberry Pi OS 64-bit on RPi 4 or later. Using a Raspberry Pi (<=3) is NOT recommended as it has quite a bit of power supply noise on the USB ports, which reduces the performance of the connected SDR. Install dependencies: sudo apt-get update sudo apt-get install airspyhf \ soapysdr-tools sox libsox-fmt-all wsjtx \ pulseaudio-utils git vim fluxbox xterm tightvncserver sudo apt-get install cmake pkg-config \ libusb-1.0-0-dev \ libasound2-dev \ libairspy-dev \ libairspyhf-dev \ librtlsdr-dev \ libsndfile1-dev \ portaudio19-dev \ libvolk-dev Build airspyhf-fmradion SDR software: ...

WSJT-X 3.x has inbuilt support for band hopping! Results RX results from an experimental version of DDX: This is super useful for monitoring FT8 traffic on multiple bands. References libmirisdr-5 WSJT-X Improved