There were two articles in QST on using an HP Opto Coupler (that part is now obsolete, probably are modern alternatives) to isolate the antenna form the oscillator so it could not become a transmitter. See:
Daniel Wissell, N1BYT, βThe OCR Receiver,β QST, Jun 1998
and "The OCR II Receiver" QST, Sep 2000.
Since the search engines have gone AI finding things like the June 1998 issue of QST has become impossible, for me at least. Maybe you have better search fu?
The schematic of that article is reproducer in this HP/Agilent App Note:
