NOAA's Advanced Technology Microwave Sounder (ATMS), passively-measures water-vapor levels, using weak signals at 23.8 GHz. NOAA uses this data for their critical hurricane forecasting. FCC Chairman Ajit Pai wants to lease the 24 GHz band for 5G networks. NOAA and many scientists, have said this will ruin the measurements, severely degrading the storm forecasts we now rely on. Ajit Pai says, f*ck off, the State Dept (!) says it's OK. With that, he's not going to attend the next scheduled meeting.
I'm not sure Ajit Pai has the authority to make such a decision alone. It might require rulings by Congress to implement. A similar situation occurred recently with GPS. A company called LightSquared wanted to use frequencies adjacent to the GPS frequencies for broadband cellular transmissions. Here is some background information:
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This appeared to end the threat:
"Lobbying and new spectrum: One last shot for LightSquared"
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shot-for-lightsquared/
It appears there may be other factors involved other than the decision of one man.
The FCC needs to be run less by crooked lawyers and more by people that understand what is needed and how this stuff (RF) works and the science of why what frequencies need to be used for what.
On a sunny day (Fri, 24 May 2019 00:17:02 -0700) it happened boB wrote in :
Spectrum is big money, here in Europe governments are auctioning spectrum for 5G now, and asking a LOT, driving the price up, as if the spectrum is theirs. Big mony may win. It is a capitalist system after all.
They are also trying to get the ham bands, I pay more every year for my license, and they make it more difficult to pay each time. Tactics
One day perhaps alien empire will auction solar system spectrum to them humans and then you work for them.
It will probably end up with NOAA and their weather forecasters being blamed for failing to forecast a hurricane after all their instruments are blinded by the sidebands of the 5G cellular transmissions.
TBH I am surprised that we have managed to preserve enough clear radio spectrum to still be able to do radio astronomy and passive water vapour detection in this era of spread spectrum mass mobile phone use.
Winfield Hill wrote in news: snipped-for-privacy@drn.newsguy.com:
Another proof that Donald J. Trump AND virtually ALL of his "appointments" are as stupid and lame as it gets.
Some idiot examines the spectral chart looking for a block of space to SELL to the people, and the science community gets screwed... again. How quaint.
Some historical background information about the amateur microwave radio frequency allocations.
Previously huge microwave segments were allocated for "radiolocation" i.e. radar with bad frequency stability. Of course, any serious user would not like to be colocated with radar, so these bands were also given to hams on a secondary basis.
With improved radar technology, these radar bands were reduces, which also reduced the amateur secondary allocations, giving large chunks of spectrum to other uses.
This is a good question.
Previously several hundred MHz wide microwave allocations were handy e.g. for running unstable 10 GHz or 24 GHz 10 mW Gunplexer frequency modulated by analog ATV.
These days generating reasonable good stability carriers with a few MHz wide digital TV signals is not a problem, so quite high SNR can be achieved with reasonable bandwidths.
Apart for some UWB (Ultra Wide Band) experiments, I do not understand, why hams would need frequency segments larger than about 10 MHz. For UWB experiment some large segment shared with other UWB services would suffice.
Realistically, what data could you put into that range at least a few hours each week. ?
At least in Europe, the 5G mm-wave allocation starts at 26 GHz.
That low range is of interest only for very rural systems.
Around 22 GHz there is a quite wide notch due to water vapor, making ground based long distance communication practically useless. Thus, very few services would like to use the 22 GHz band.
As long as the spectral purity for 24+ GHz systems are very good, this should not interfere with 22 or even 23.8 GHz sensors. Of course, if the satellite sensor front end is as wide as 20 to 30 GHz, all bets are off.
On a sunny day (Sat, 25 May 2019 09:35:05 +0100) it happened Tom Gardner wrote in :
If you are at sea on a boat that would be great, if it is a lot cheaper than iridium etc.. I mean places out of reach of 4G and 5G towers. Competition will get the pices down.
Jan Panteltje wrote in news:qcb1rb$ati$ snipped-for-privacy@dont-email.me:
ViaSat1 covers North America and part of Canada. I do not know what areas ViaSat2 or any newer placements service.
But ViaSat1 is like $79 a month and I think it is like 15Mb/s. That is on what was the fastest satellite up there until they launched more. The first was over 140Gb/s.
I have serious doubts that Musk's devices will be delivering
50Mb/s ever.
And what is he going to do for ground stations?
Every satellite would need access to an Earth based/Internet hooked Satellite Gateway with dishes and feeds onto the main backbone.
ViaSat has Earth Gateway stations in 15 US cities from anchorage to Honolulu. Each one has two 8 meter dishes and a set of ten racks of gear for the hooks. It is Ka-band.
You might get sufficient usage with a digital amateur TV (DATV) repeater in a large city.
I haven't recently heard much of DATV experimentation. About a decade ago, there were some experimentation using DVB-S. The DVB-S was initially designed for satellite reception and thus is not very good in handling multipath, preferably line-of-sight paths would be preferable.
OTOH, DVB-T (or other multitone OFDM) is designed for terrestrial multipath environment and would be better suited for DATV.
A single program stream could be put into a 2 MHz bandwidth or multiple program stream in a 8 MHz multiplex, so not much frequency demand on higher frequency bands.
That is partially a myth. While it is true that vegetation will absorb higher frequencies quite effectively In urban areas the higher frequencies are reflected very well from hard surfaces and the signal level drop is not much worse than on lower frequencies.
While the gain is a good quality measurement for transmitting antennas, for receiving antennas, the antenna capture area is the critical thing. Of course gain can be converted to capture area and visa versa for a specific wavelength.
The antenna capture area is proportional to the square of wavelength, thus for a constant field strength the received power will drop rapidly. The capture area for a half-wave dipole is little more than
0.1 square wavelengths. On HF, the capture area is as big as hangar doors, while up in the microwave bands about the size of a coin, thus much less power is delivered to the receiver.
To increase the received power, an array of dipoles can be used. This may also increase directivity (and gain) which might be desirable or undesirable feature depending of the situation. Too much directivity is a bad thing, if multipath reflected signals come from different directions. One way o handle this problems to use antennas with steerable radiation patterns, such as MIMO antennas.
Every time someone announces some new satellite based internet system, I have wondered, where do you get sufficient spectrum to handle the large number of simultaneous customers. The whole idea of any cellular system is the frequency reuse, so you want to keep the cell size small and avoid spilling over signals into neighbor cells. With satellites, one would need very good steerable antennas which is hard, if the satellites are small.
OK, so don't even try to serve urban customers, since the local cell towers will handle them with lower cost. What is left, customers on high seas, in the tundra and in the desert. But are these customers capable of paying for the satellite constellation ?
Since the oceans occupy a huge part of the earth, thus LEO satellites will fly over the water for quite a long time each orbit, Does the island and cruise ship users generate enough revenue ?
I suspect if it isn't worked out politically, it will be worked out technically. I saw my first 5G antenna about 3 weeks ago here, in Panama City Fl, about 1500ft from my house. Then saw the second one about 10 days later, about 1 mile from my home I don't know what it means to me, I'm frugal, paying $40 a month for my phone and $24 a month for my wife's phone and $45 a month for Internet service. Not sure I want to pay more for something I don't have a need or desire for, I already spend to much time in front of a screen. But maybe I'll have a better deal with cable and phone bundle? They are putting in 5G because the 4G system was so damaged by the hurricane, that they decided to rebuild with 5G. They have the 4G working well enough, you can stream Youtube videos without buffering. Service was very poor for 3 months, which they gave us without charge. Anyway, I'm fine with 4G, but I was fine with my flip phone too!
Mikek
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On a sunny day (Sat, 25 May 2019 20:51:34 +0300) it happened snipped-for-privacy@downunder.com wrote in :
Yes, I did (and do) the DVB-S stuff:
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Modified version now for QO100 satellite.
True, but I know little about DVB-T, did read up on it. but have not desihned or build anything for it, I do have plenty DVB-T USB sticks ;-)
This may interest you for spectrum usage, lots of experiments going on with DVB-S2 and some DVB-S
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Anyways a few MHz is enough, lower symbolratea are possible.
Antenna height rules of course. There is a 70 cm repeater network here that covers much of the NE part of the country
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and an other one that does the west. Not much here on 24 GHz that I know about? QO100 satellite is a geostationary sat and can be accessed with a small commercial TV dish and just a few watts for SSB. from almost anywhere.
2.4 GHz uplink. Even S Africa and Brasil is easy from here, but local chatting via that sat happens too, all of Europe, Russia, Middle East. So much for the large antennas....
Yes good question, Elon Musk making profit ? SpaceX does. Geostationary sats would be an other approach, dish pointing at sea is possible, for 1000$ you have a stabilized pointing system to a geo sat, no problem for a cruiseship, gives them TV too. I am sure somebody at SpaceX did the math... We will see where it goes.
Or in many locations on land where the infrastructure is inadequate.
While I doubt investment could be recouped from maritime use alone, I expect the land-based demand to be *much* more than necessary - hence the question.
For cellular systems, a prime figure of merit is bits/s / MHz / km^2, i.e. how closely the Shannon limit is approached plus how densely the frequencies can be reused by adjacent cells. I would expect something similar for this system.
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