Where exactly is the Fumb-26 "Tunis" receiver mounted on the XXI?

[difool2]

Twice in my current patrol I got bushwhacked by planes while running the snorkel on the
surface while recharging (XXI April 44). The Fumb-26 never sang on either occasion
(and the planes sunk me in both cases-yes I reloaded the career so sue me). Odd
thing is that I haven't heard a single peep from the detector during the entire mission
(and not just in those 2 instances). I also didn't see any gizmo mounted on the snorkel,
so is it there or is it on the conning tower somewhere? If it isn't on the snorkel it kind of
defeats the purpose eh? If it is, is it working properly, or is it just an obsolete piece of
junk which can't detect the latest frequencies? I'd also like to know the code for all
the receivers (for the careers.cfg file) so I can add them in that way. TIA.