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

Scott McGrath smcgrath at starry.com
Thu Jan 20 03:34:25 UTC 2022

Um the Lightsquared monster is back stronger than ever however it has a new
name Ligado Networks

Yes we now have something which everyone agrees will hose every civillian
GPS receiver out there.   But hey thats the user’s problem.

I’m glad i know how to use a sextant….   Perhaps someone will come up with
a low priced INS.   The 747 was the last airliner which used a INS.    Of
course a improperly initialized INS was responsible for the Korean Air
shoot down incident….

Of course this will also hose our NTP servers and 802.11ad/ay networks and
any other network kit that uses GPS.

On Wed, Jan 19, 2022 at 9:34 PM Bryan Fields <Bryan at bryanfields.net> wrote:

> On 1/18/22 9:03 PM, Brandon Martin wrote:
> > 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.
> The issue is not one of out of band emissions, but rather close but strong
> signals near the receiver pass band.  This can cause compression of the
> first
> RF amplifier stage and de-sensitize the receiver so it cannot hear the
> intended signal.  I won't get into the physics, but it is difficult to
> realize
> an effective filter that will permit 4200-4400 with low loss and attenuate
> everything else starting at 4200 MHz and down.  The narrower the filter is,
> the higher the loss is. The greater the stopband attenuation is, the more
> elements required and more ripple is present in the pass band.  Now granted
> for avionics, this is doable in the thousands of dollars, but older radar
> altimeters will not have this level of filtering, nor can you slap a
> filter on
> avionics without manufacturer support.
> Further complicating this, radar altimeters in the 4200-4400 MHz band are
> frequency modulating continuous wave transmitters.   In this configuration
> the
> frequency is not closed loop controlled, it can be anywhere in the 200 MHz
> band, as it's modulating a free running VCO nominally at 4300 MHz. This is
> a
> non-issue as the transmitter is used for the receiver reference, so they
> are
> locked to the same free-running oscillator.
> Only in recent avionics has the receiver been improved via DSP circuits and
> FFT to do real time spectral analysis and pick out the right receive
> signal.
> The older altimeters out there use simple zero crossing counting to
> determine
> the frequency of the strongest signal.  This leaves them open to potential
> interference by strong near band signals. Exasperating this is the poor
> filtering on the RF receiver in 99% of altimeters when dealing with wide
> band
> signals.
> So can this LTE at C band work? Yes.
> Will it require upgrades to avionics and standards? Yep.
> Last time this sort of change out was needed Sprint/Nextel bought every
> major
> public safety agency new radios.  One could plot the decline of Sprint
> stock
> to an uptick in Motorola stock.
> This reminds me of the Lightsquared case where they were using adjacent
> spectrum to GPS for low speed data from satellites, and wanted to add in
> repeaters on the ground, or an ATC/ancillary terrestrial component.
> Sirrus XM
> does this, in tunnels and such and it's just the rather low power repeater
> of
> the same signal from the satellite. Lightsquared wanted this the be a high
> power LTE signal, which wouldn't "fill in" their satellite signal but make
> an
> LTE network they would sell access on.  Do to the proximity to the GPS
> bands
> and the rather poor selectivity of the GPS receiver, it would have
> dramatically limited GPS performance.
> The issue here is that Lightsquared was too small.  The establishment
> wireless
> carriers know that commissioners don't work at the FCC for life, and have
> paid
> lobbyists crawling all over capital hill.
> --
> Bryan Fields
> 727-409-1194 - Voice
> http://bryanfields.net
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