I only passed my foundation in 2021 so it must have been mentioned in something quite recent.
The RSGB has some copies of older (A)/(B) licence booklets on their website - no mention of it in there that I can see, only the Charing Cross restriction.
Ah, like AST Spacemobile 
No proper satellite links like real comms sats run by less friendly countries who donāt want to give assorted spooks a direct feed. The radomes are not to protect the dishes from the WX but so you canāt see which satellites over āplaces further Eastā they are listening to Companies like AST Spacemobile and Starlink donāt get to refuse āpoliteā requests from Uncle Sam, so you donāt need to monitor the sats, just get the operators to tell you who is doing what.
Which brings back the great UK spook leak of the 80s/90s. At these places there are may non-UK staff from firendly governments working with the UK, predominantly US citizens, military and others. Not surprisingly, many technical people working in high tech comms are/were radio hams. The UK used to offer G5 calls for reciprocal licencees. You came to the UK, and went through the process and got yourself a shiny G5ALX callsign. (@GM5ALX) Of course you then went in the callbook with your name āA. J. Spook, 23 Letsby Avenue, Harrogate, HG1 1AAā. Nothing sinister about that. Apart from the fact you could take the callbook and extract all the G5 calls in HG1 postcode and that would give you a list of all the possible CIA/NSA/USA contractors living near Menwith Hill. Do with that what you want for your nefarious interests. Repeat for all G5s near any military site and you have a pretty good list of targets.
When someone figured this out in UK Spook Control, all G5 reciprocal calls were rescinded and no alternatives offered. It wasnāt a case of give these people G4/G6/G1/G0 calls because all you then did was checked the follow up callbooks and check to see which G5 of 23 Letsby Avenue now had a G0 call and you can still track the old people you knew of just not the new.
It makes me smile to remember this when I see all the new re-issued G5 calls in the UK. Iād be reluctant to have such a call as itās probably still on assorted files in FSB/KGB offices and could still mark you out as āsomeone of interestā.
Not all G5 calls were possible spooks, a lot were genuine amateurs who had emigrated to the UK.
Thereās nothing in the BR168 and OF168 booklets I foundā¦ in my hazy memory there may have been limits on 70cms operation during the setup and calibration of the PAVE PAWS units that replaced the old golfballs at Fylingdales in the mid-90s.
I picked G5 as:
Although if Iād known theyād issue Japanese callsigns, I mightāve gone for one of those.
