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.
2 at SFO in good weather. (Where it doesn’t matter if they work). 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. They also have main lobes approx 80* wide so they still function when the plane is in 40* of bank. Ms. Lady Benjamin PD Cannon of Glencoe, ASCE 6x7 Networks & 6x7 Telecom, LLC CEO [email protected] "The only fully end-to-end encrypted global telecommunications company in the world.” FCC License KJ6FJJ Sent from my iPhone via RFC1149. > On Jan 18, 2022, at 2:25 PM, Jay Hennigan <[email protected]> wrote: > > On 1/18/22 12:29, Michael Thomas wrote: >> I really don't know anything about it. It seems really late to be having >> this fight now, right? > > From a technical standpoint it seems to me to be a non-issue. There's a 220 > MHz guard band. 5G signals top out at 3980 MHz and radar altimeters operate > between 4200 and 4400 MHz. > > If a signal 220 MHz away is going to interfere, then radar altimeters on > other aircraft operating in the same band would clearly be a far greater > threat, and those radar altimeter signals will be rather numerous near > airports. In other words, if non-correlated signals 220 MHz away are going to > interfere, then signals within the same band are going to be a far greater > source of interference. > > Radar receivers are typically some form of direct conversion with rather good > selectivity, synchronized to the frequency of the transmitted pulse. In > addition, radar altimeter antennas are pointed at the ground, perpendicular > to the horizon. Cell site antennas by design are aimed more or less toward > the horizon, not pointed straight up at the sky. > > There's also an existing FCC mobile allocation from 4400 to 4500 MHz directly > adjacent to the aeronautical radar band on the high side with no guard band, > yet no complaints about that. > > IMNSHO, the concern that 5G cellular signals will cause airplanes to fall out > of the sky has about this >< much more credence than the concern that 5G > signals cause coronavirus. > > It shouldn't be that hard to instrument an aircraft with test equipment, buzz > a few operating cell towers, and come up with hard data. > > -- > Jay Hennigan - [email protected] > Network Engineering - CCIE #7880 > 503 897-8550 - WB6RDV
