[queued] T4.x based SDR with Hi res 7" touchscreen, 4096 FFT


A few of these have been built now. Receive only at the moment while waiting for suitable transmit hardware to developed.

This SDR uses the Teensy 4.1 (most often) with the PJRC audio card. OpenAudio_Library used with only 32bit floating point functions. Configurable FFT size ad sampel rates but normally running 104KHz sample rate with 4096 I &Q FFT. ~20% peak CPU, around 8% average @ 600MHz. Limitation is RAM for the audio buffers required. At 79% right now.
For the 7 inch RA8876 based touchscreen, 1024x600, using a custom gesture engine allows decent touch-only experience. Can add I2C encoders (with RGB LED) as well as normal low and high res encoders. A hi res for VFO is popular along with a smaller one designated as a multi function knob, can add several more for dedicated functions like AF ad RF gain. For now I am using the QRP-Labs HF QSD receiver board. A si5351a or c (with OSCXO/GPSDO) for the PLL. I/Q audio goes to the Teensy audio line in. I am i early stages of working out how to use this SDR as a PC replacement (full control head with I/Q audio processing) for the Hermes Lite 2 (HL2) low cost 0-38MHz SDR transceiver. It is a headless compact SDR with only the ethernet for connection.

I have 3 main usage scenarios set by configuration variables/defines.

1. SDR transceiver - RX only at the moment but the UI framework is ready for full RX/TX when the TX hardware comes around later.

2. Panadapter - currently working on the 8.2MHz buffered IF output from an Elecraft K3 transceiver with many transverters attached. Uses serial CAT control. This is more than just basic Panadapter feature set as it also mirrors some of the radio's indicators like AGC, RIT/XIT etc. This is a stepping stone to full control head functionality.

3. (Remote) Control Head - in progress - replace the front panel of selected radios using CAT connection, or in the HL2 case, use the ethernet stream and/or a custom FPGA connection, TBD.

Using the RA8875 and RA8876 displays I was able to leverage the display controller's Bit Transfer Engine (BTE) to let the display do block moves to create a smooth scrolling effect without burdening the CPU. This is for both spectrum and waterfall. The spectrum code is relatively standalone, table structure driven, as is the whole UI framework, and is resizable with many controls. I have even run 2 windows so far though more work required for that to go beyond POC. There is plenty of CPU for it.

GitHub code and Wiki


Below are 2 builds, one with 4.3" RA8875 touchscreen (800x480) and I2C RGB LED encoders, targeted as a Panadapter. The larger sloped box is a 7inch RA8876 (1024x600) touchscreen with SV1AFN preselector for 10 bands HF coverage, preamp, digital step attenuator, Si5351A wit TCXO PLL, and QRP Labs RX board.

K7MDL - April 2021 7in RA8876 SDR.jpg