For those who want to build their own superheterodyne transceiver, the Minima may fit the bill.
Designed by Ashhar Farhan, the schematics are freely available online.
Minima Schematics: http://www.phonestack.com/farhan/minima.html
Backup Archive of Schematics: https://www.freelists.org/archives/minima/01-2016/pdfavh3bHrUb6.pdf
Minima Arduino code on Github: https://github.com/afarhan/radiono
Discussion of Minima on FreeList: https://www.freelists.org/post/minima/Minima-PCB,24
PCB for Minima builds: https://yo4hhp.wordpress.com/2014/01/22/pcb-for-minima-general-coverage-transceiver/