HF

It's a Training Ground for Engineers (And We've Been Ignoring It) Let's drop the nostalgia and say something uncomfortable: If you think ham radio is just people talking into microphones, you're not just wrong - you're overlooking one of the most hands-on, intellectually rigorous engineering playgrounds still accessible to individuals. Because amateur radio isn't about conversation. It's about understanding how information survives reality. And reality is hostile. Signals Don't Care About Your Abstractions Modern software engineers live in a world of clean abstractions: APIs work (until they don't), packets arrive (until they don't), networks are "just there." ...

Ismo (OH2FTG) has praised the STM32's ADC quality multiple times, and I finally decided to give it a go. I usually stick with Waveshare RP2350-Zero boards, but the RP2350 ADC performance is limited to under 10 ENOB. With the STM32H562RGT6, we're able to achieve ~13 ENOB using 16× hardware ADC oversampling, with potential headroom to push this even further. By sampling the Si4732's SSB output using the STM32H562RGT6 ADC and exposing the audio samples to the host via a "virtual" USB UAC-2 device, we get the following RX results: ...

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. ...

Related articles: Proper Single Transistor LNA for HF A Sustainable Radio Design? Design We are finally going to build a QSD RX! Here is the rough schematic I am thinking about: References MC1496 Information HSDAOH on RP2350 (see internal_adc section) This way we can continue using RP2350 instead of moving to something like STM32H5 immediately PicoRX Simulations (also for DSP code)

Note: This HF LNA design is inspired by PY2OHH designs and mcHF work. Previous article: Single Transistor LNA for HF - it cut a corner when it came to output impedance matching ;) Design The idea that a single-transistor preamp with 10 dB gain is more than enough for HF comes from Gajendra Kumar (VU2BGS). As a new "designer," I am often overwhelmed by the available design paths, so guidance from an elmer is crucial. ...

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. user@rpi:/etc$ cat /etc/os-release PRETTY_NAME="Debian GNU/Linux 13 (trixie)" NAME="Debian GNU/Linux" VERSION_ID="13" ... 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 \ libqt5websockets5 cmake build-essential 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: ...

Future radio receiver design ideas (from Ismo, Pete and other folks): Antenna ➔ (BPF) ➔ BFR93A based pre-amp from mcHF project ➔ MC1496 (Mixer) ➔ 455 kHz IF ➔ Ceramic filter SMD (HCI) ➔ 'IF amplifier' (20-40 dB gain?) ➔ Overclocked Pico 2's ADC (3+ MSPS) ➔ Digital down-conversion and processing in digital domain ➔ Expose the processed audio samples over USB (Pico 2 acts as a sound card). Benefits: This enables reception of SSB and CW signals! The 455 kHz IF with digital processing gives us the best of both analog selectivity (ceramic filter) and digital flexibility. ...

Shipping hardware internationally is a hard, labor intensive, and overall a frustrating process - especially more so these days. Here is our plan to supply the DDX to customers: Make the hardware files free / low-cost. The users will be able to order fully assembled boards from JLCPCB or other vendors on their own. Required a small licensing fee for the software firmware part. This is how we get to keep the hobby self-sustaining! ...

I recently spotted the Tokmas CI7N170SM TO-247 part on LCSC. It seems like a pretty neat part for building non-QRP HF amplifiers! This could be a better part for our Baby QRO amplifier. Datasheet Excerpts The full datasheet is available here. Comparison In comparison, here is what a professional RF part (MRF300AN) looks like: That 272W maximum power dissipation figure is crazy good but switching characteristics are not that great (fast).

Circuit: DDX-Commercial-7 Antenna: Small jumper cable attached Initial Results 10m: 36 dB on WSJT-X audio meter, on quiet and also with nearby beacon on !!! 12m: 36 dB on audio meter, on quiet and also with nearby beacon on !!! 15m: 46 dB on audio meter on quiet, 65 dB with nearby beacon on - OK 20m: 44 dB on quiet, 65 dB with beacon on - OK 40m: 40 dB on quiet, 60 dB with beacon on - OK ...