I have purchased the PTT cable from Pileup to connect my SUNSDRQRP to XPA125B Amp.
Do I need to isolate the PTT with diode protection and use the computer to key the amp?
I thought this cable has an opti-coupler to isolate the audio already?
I have attached the diagram found in the manual

The protection is included in the cable. Connect to the computer, supply CAT to that port and set any PTT delay required in the software.