ESP32 Phasing SDR Board
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///////This is a work in progress the board and firmware still have bugs////////
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Standalone software-defined radio front-end based on an ESP32 and an analog phasing (I/Q) receiver. The goal of this project is to provide a compact HF SDR/panadapter board with:
Analog RF front-end (ring mixers + handmade transformers)
High-quality 24-bit baseband digitization
On-board audio output and 4" TFT UI
Direct I/Q output for connection to a PC SDR program
The PCB shown here is already fabricated and under test.
Main Features
ESP32-based SDR platform
Runs the demodulation / UI firmware (AM, SSB, CW, etc.).
Communicates with ADC, DAC and TFT over I²S / SPI.
RF front-end
SMA antenna input.
Ring mixers built with BAT01599R Schottky diode quads.
Handmade RF transformers for LO and RF ports.
RF pre-amplifier using a 2N3904.
Baseband section
Active I/Q low-frequency amplification with a TL072 dual op-amp.
I/Q output header for connection to a PC (panadapter / external SDR).
Data conversion
24-bit audio ADC for digitizing baseband
Audio DAC for speaker/headphone output
Audio output
On-board audio power stage for speaker or headphones.
Dedicated audio out connector.
User interface
4" TFT display for spectrum / waterfall / UI.
Rotary encoder for tuning and menu navigation.
Multiple push buttons for mode / band / configuration.
Power
USB-C connector for power and data.
On-board PT4056 Li-Ion charger.
Battery connector footprint.
Power switch and status LEDs.
Hardware Overview RF Section
SMA input connector feeding the RF front-end.
RF pre-amp based on a 2N3904 transistor.
Double-balanced ring mixers using BAT01599R diode quads.
Handmade transformers for:
RF input matching
Local oscillator distribution
I/Q baseband coupling
Baseband & Conversion
TL072 dual op-amp used as baseband (I/Q) amplifier and anti-alias filtering.
I/Q signals:
Routed to the on-board ADC.
Also exposed on a dedicated header to feed an external PC-based SDR.
24-bit audio ADC connected to the ESP32 via I²S.
Audio DAC connected via I²S to drive the audio chain.
Audio & UI
Audio amplifier stage for speaker / headphones.
4" TFT display:
Used to draw FFT / waterfall and UI elements.
Rotary encoder + push buttons for:
Frequency tuning
Band selection
Demodulation mode and settings.
Power Management
PT4056 Li-Ion charger IC.
USB-C connector for charging and powering the board.
Battery connector footprint (single-cell Li-Ion).
Power rails for RF, analog and digital sections with appropriate decoupling.
Firmware
The firmware is written for the ESP32 and includes:
I²S double-buffered capture from the ADC.
I²S audio playback through the DAC.
Demodulation algorithms for AM, SSB and CW using I/Q phasing.
FFT and waterfall display on the 4" TFT.
Encoder and button handling for tuning and configuration.
Optional I/Q streaming to a PC through the I/Q output.
