Related articles: Proper Single Transistor LNA for HF A Sustainable Radio Design? We are finally going to build a QSD RX! Here is the rough schematic I am thinking about: References: https://www.n6qw.com/MC1496.html https://github.com/steve-m/hsdaoh-rp2350 (see internal_adc section) This way we can continue using RP2350 instead of moving to something like STM32H5 immediately https://github.com/dawsonjon/PicoRX/tree/master/simulations (also for DSP code)
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! ...
Our WSPR beacon design works fine even on the 4m band (~70 MHz) . The key is to use a 25 MHz high-quality TCXO, like the 25 MHz HCI 0.5ppm TCXO! 2m WSPR is still out of reach for now - see the following sporadic decodes. Of course, the next challenge is to get 2m WSPR beacons working 100% reliably at a low cost. ...
The usage of ready-made coupled inductors in RF designs was pioneered by Jim Veatch in his award-winning RF amplifier designs. For Baby-QRO applications, we can use Wurth 744851330 coupled inductor. For 5W / 10W RF amplifier applications, we can use Bourns SRF1260A-4R7Y coupled inductor. Recently we were able to utilize very cost-effective YJYCOIN YPRH1207C-4R7M Chinese coupled inductor with excellent results. With our current Digital Amplifier designs, this Chinese coupled inductor works even at ~75 MHz. ...
Our 6m WSPR beacon design works fine now. The key is to use a 25 MHz high-quality TCXO, like the 25 MHz HCI 0.5ppm TCXO! 2m WSPR is still out of reach for this VFO design - see the following drifty screenshots: While WSPR is no good, 2m FT8 works pretty fine! Of course, the next challenge is to get 2m WSPR beacons working at a low cost. ...
I am posting an early design sketch of a 2m WSPR beacon. Here are the key points: 25 MHz HCI 0.5ppm TCXO powering the Si5351 module instead of the 26 MHz TCXO. If this fails, we can use a 10 MHz OCXO instead (a bit out of spec but works fine). Tokmas CID10N65F GaN FET might work @ 144 MHz as the 'final'. If not, use Mitsubishi RD15HVF1-501 MOSFET as backup. ...
I am posting an early design sketch of a 6m WSPR beacon. Here are the key points: 25 MHz HCI 0.5ppm TCXO powering the Si5351 module instead of the 26 MHz TCXO. If this fails, we can use a 10 MHz OCXO instead (a bit out of spec but works fine). Tokmas CID10N65F GaN FET should work @ 50 MHz TI UCC27614 or Onsemi NCP81074 gate driver Results: To be built and tested soon! ...