Roman,

I also have concern and posted previously this question regarding Receiver Input Protection.
The block diagram you reference shows that the unused ports of the relays open, not grounded.
I think a true schematic, or PCB layout, would be better suited to resolve this question.

Tom W3FRG

Hello Tom.
You are correct, it's not a complete schematic, there are also 3 additional relays which:
1. Ground each antenna port when TRX is switched off
2. Ground VHF port when you operate on HF
3. Ground HF ports when you operate on VHF