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

[Jay Hennigan <jay () west net>]

On 1/19/22 01:53, Lady Benjamin Cannon of Glencoe, ASCE wrote:
> Jay, one thing you’re missing is that a maximum of 2 (and almost always 1) radar altimeter will be in use per airfield, 
> as one aircraft will be landing at a time.

Really? I was under the impression that radar altimeters were pretty 
much always active during flight. If not, what triggers the "PULL UP - 
TERRAIN" audible warnings that are often heard on CVR recordings just 
before an airplane flies into cumulo-granite weather (mountains) miles 
from an airport?

If in fact they are only used for IFR approach, is there a lockout to 
ensure that the radar is only active on approach? If pilots forget to 
turn them off after landing, does the radar transmitter automatically 
shut itself off?

> Apparently some old gear has trouble with even a 500MHz guard band, which I also find astonishingly bad for any time, 
> but a lot of aviation tech is truly from another century.

This is absolutely horrible receiver design on equipment critical to 
aviation safety and it's surprising that tighter specs weren't enforced. 
That adjacent spectrum hasn't exactly been silent until now. It's been 
in use for decades going way back to Bell System TD-2 microwave that at 
one point criss-crossed the country.

> They also have main lobes approx 80* wide so they still function when the plane is in 40* of bank.

That makes sense.

--
Jay Hennigan - jay () west net
Network Engineering - CCIE #7880
503 897-8550 - WB6RDV