What do you think about this airline vs 5G brouhaha?

Brandon Martin lists.nanog at monmotha.net
Wed Jan 19 02:03:14 UTC 2022

On 01/18/2022 20:08, Michael Loftis wrote:
> Remember that the RA is sub 1W looking for reflected emissions. It’s 
> very possible the ground equipment for a cell base station to have 
> spurious harmonics…where they land requires more RF engineering chops 
> than I’ve got, and would obviously be very system dependent. So yes in 
> my understanding due to the RF voodoo of how they transmit and receive

This is run-of-the-mill testing for not just transmitters but anything 
that could possibly, maybe, emit RF energy in the USA.  The out-of-band 
(spurious emission) limits are quite strenuous, and the test criteria 
are specifically designed to catch even fairly intermittent blips that 
might crop up just about anywhere let alone in a band of particular 
interest.  There's a reason (just about) all FCC compliance houses have 
70GHz spectrum analyzers even if they don't normally look at intentional 
emissions above 6 or so.

One thing the FCC could potentially do to wipe some egg of their 
collective faces, here, is mandate that transmitters operating in this 
newly allocated wireless band face additional scrutiny for spurious 
emissions in the radio altimeter band as well as the guard band between 
the two services and a similar bandwidth above the radio altimeter band. 
  If the quasi-peak detector runs across that swath for an hour while 
the operating conditions of the device being tested are continuously 
varied both within and somewhat outside its normal and even 
extraordinary (but functional) operating range and still doesn't see 
anything that isn't outside the femtowatt range, you're probably good. 
FAA and aviation industry can even advise on these standards.  That's 
not unheard of and a good example of industry cooperation.

Note that this would be above and beyond the existing general rules for 
spurious emissions that are already tested as part of pretty much any RF 
transmitter in the USA.

I'm curious at what point the possibility of spurious emissions from an 
old-fashioned TVRO C-Band receiver becomes concerning.  It would be very 
sporadic, but the gain off the ground station dish is rather 
non-trivial.  AFAIK, the design of most receivers would mean it would 
have to be a modulation product of two LOs, but I suspect it's possible 
to have something come within 500MHz of this band just like this 
wireless allocation does.  Those users have been around for 35+ years 
and are widespread and unlicensed (as they are receive only).

Brandon Martin

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