This is a motherboard that mounts on the back of a 7" RA8876 touchscreen display from buydisplay.com.  Holes are provided so that this PCB can also plug onto a 4.3" RA8875.  

SDR project info at https://github.com/K7MDL2/KEITHSDR.  It has the code, BOM, these PCB files, pictures, and Wiki pages.

Extensive information can also be found on the Forum site at https://groups.io/g/keithsdr.

The orignal 7" PCB here (V2.1 Dec 30, 2022) work fine but had 0.5mm hole misalignment.  V2.2 was produced on Jan 14, 2023 to correct that and while fixing that I made many other small changes including moving back to 4 layers for more noise sheilding, adding an Antenna relay driver transistor to match the new code, pairs of 2-pin headers for 3.3V, 5V and 12V switched power for accessories.  Most connectors were shuffled around for best trace lenght and routing to reduce audio or usb data noise, and minimize emitted noise.  power now supplied to the proto area top row (3.3, 5, 12, and GND on 2nd row).  GND is on a 3rd lyer ground plane. Copper pours on bottom and top with lots of stitching via.  USB and enet on inner layer along with audio and some others.  Cutout in front of enet/USB jack removed, was not needed.

There are 2 SDR variants on the project forum:

1. Simple - ("Keith's SDR").  It uses a lower cost smaller display.  This PCB will not work with the display used by default.

2. My derivation SDR_RA887x is specifically for the RA8876/RA8875 displays and supports this PCB.  It takes advantage of the RA887x display controller capabilities reducing CPU overhead for needed spectrum & waterfall graphics performance.  This motherboard is for the RA887x variant only.  Uses multiple FFTs up to 4096IQ from OpenAudio_Library which is now 32bit floating point.  USB and analog audio connections, compatible with WSJT-X using the Elecraft K3 CAT radio interface.  Can use a variety of RF hardware, I am currently using the RS-HFIQ 4W headless SDR transceiver.  Connection to the RS-HFIQ is by analog Line In and Line Out cables and the Teensy USB Host for serial control. The RS-HFIQ covers 80-10M bands.  There is support for a range of RF side hardware other than the RS-HFIQ and adding something new should be minimal effort.  This includes attenuators, bandpass filters, various Si5351x PLLs, preamp and antenna switching, PTT, mic audio.  

The attached project files includes a BOM and picture of a working assembled DIY SDR.  The display listed is the 4.3" RA8875.  There is a 4.3" sized board on this web site for it from N0CTL.  I have a slightly updated version to be released soon here.

The 7" Display I use is from buydisplay.com.  Model ER-TFTM070-6 is 1024x600 dots 7 "color tft lcd module display with RA8876 or LT7683 controller board. 

SPI 7"TFT LCD Dislay 1024x600 w/RA8876 OPTL Capacitive Touch Screen (buydisplay.com)

Order options to choose are:

Interface: Pin-Header-Connection-4-wire-SPI

Power Supply: VDD=5.0V

Touch Panel: 7" Capacitive Touch with Controller

MicroSD Card Interface: Pin Header Connecton

Font chip: none

The Teensy 4 related parts are the Teensy 4.1 CPU module and the Rev D Audio Module.  These plug or solder into the motherboard.  My GitHub WIKI has a lot of info as well as the forum linked above.

- Mike K7MDL