[Milsurplus] AN/PRC-66 Guard Channel Module

[Morrow, Michael A.]

Has anyone ever come across an RT-865D/PRC-66 that contained the guard
channel (243 mcs) module, or come across these modules alone in surplus?  I
have two RTs without this module, and I've been led to believe that this was
an optional module that was not often installed in these sets.

Thanks,
Mike / KK5F