HF

My new favorite HF antenna is the 1/4 Wave HF Vertical DX Antenna with 2 Elevated Radials. It is NOT the most portable antenna (an EFHW wins there) but it is the easiest HF antenna to construct! It is easier to construct, install, and tune than even the basic dipole antenna! It takes less than 15 minutes to build and get on the air with this HF DX antenna! No impedance transformer is required. After trimming, the antenna can directly feed 50 Ω coax. A 1:1 common-mode choke (coax choke works too) at the feedpoint is recommended but NOT absolutely required at low power levels. ...

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: ...

Photographers often say: The best camera is the one you have with you. DDX-UNO ("Digital Pixie") applies the same philosophy to amateur radio. The best HF transceiver isn't necessarily the most powerful one. It's the one you remembered to bring. Most HF stations remain at home. Portable radios often require batteries, coax cables, antenna tuners, protective cases, and a backpack full of accessories. The result is that many operators leave their radios behind. ...

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)