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 <br...@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 >
