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tropo scatter antenna systems for point-to-point over the horizon data links still exist, and are not as absolutely gigantic (but are still huge and unwieldy co

tropo scatter antenna systems for point-to-point over the horizon data links still exist, and are not as absolutely gigantic (but are still huge and unwieldy compared to portable two way satellite): https://www.militaryaerospace.com/communications/article/14067632/troposcatter-communications-antenna https://www.militaryaerospace.com/communications/article/140... https://www.mwrf.com/technologies/systems/article/21846099/troposcatter-system-maintains-50mbs-connection-over-100-miles https://www.mwrf.com/technologies/systems/article/21846099/t... You still need REALLY high power amplifiers on the Tx on each end (not too much different from a giant high power tx amp on like a 7.3 meter two-way geostationary satellite earth station). The modems are a lot better than they used to be. Better use of advanced FEC and adaptive coding/modulation systems, very similar also to advanced two way SCPC/MCPC type two way satellite modems. Some of the same manufacturers make subsystems for both industry segments. One of the reasons why the US DoD is so enthusiastic about Starlink (and when available, LEO systems from telesat, oneweb, etc) is that future polar orbit coverage will provide a huge amount of bandwidth to sites at very high latitudes where using geostationary-based systems is problematic due to elevation angles. some links for historical stuff related to data/comms for radar sites in alaska and northern canada: https://en.wikipedia.org/wiki/Distant_Early_Warning_Line https://en.wikipedia.org/wiki/Distant_Early_Warning_Line https://en.wikipedia.org/wiki/North_Warning_System https://en.wikipedia.org/wiki/North_Warning_System

blantonl 5y ago
A very active tropo scatter system still in use today is the SNOTEL network, which are snow level and precipitation sensors spread all throughout very remote and mountainous terrain in the Western US and Canada. They operate on 40.67 MHz are still actively in operation today. https://www.wcc.nrcs.usda.gov/snow/ https://www.wcc.nrcs.usda.gov/snow/
- walrus01 5y ago
  I imagine the information needed for small integer data from a sensor of rainfall mm/hour and snow gauge, etc is a very low data rate... What channel widths and modulations are they using in the 40MHz bands?
  - blantonl 5y ago
    Snotel is a 9 khz channel bandwidth, BPSK data at 4000 bits per second
jacquesm 5y ago
I think one of the main reasons why they are so enthusiastic about it is that the cost of these satellites is low enough that there are so many of them that taking them out is much harder than with even the most hardened military satellites of which there will never be significant numbers. If the cost of the munition outweighs the cost of the satellite then your satellite network is pretty safe.
- walrus01 5y ago
  That is a good point, and generally they want as many paths/redundancies as possible. The DoD has its own molniya orbit satellites, quite recently launched, but capacity is limited.

blantonl 5y ago

A very active tropo scatter system still in use today is the SNOTEL network, which are snow level and precipitation sensors spread all throughout very remote and mountainous terrain in the Western US and Canada. They operate on 40.67 MHz are still actively in operation today. https://www.wcc.nrcs.usda.gov/snow/ https://www.wcc.nrcs.usda.gov/snow/

walrus01 5y ago
I imagine the information needed for small integer data from a sensor of rainfall mm/hour and snow gauge, etc is a very low data rate... What channel widths and modulations are they using in the 40MHz bands?
- blantonl 5y ago
  Snotel is a 9 khz channel bandwidth, BPSK data at 4000 bits per second

jacquesm 5y ago

I think one of the main reasons why they are so enthusiastic about it is that the cost of these satellites is low enough that there are so many of them that taking them out is much harder than with even the most hardened military satellites of which there will never be significant numbers. If the cost of the munition outweighs the cost of the satellite then your satellite network is pretty safe.

walrus01 5y ago
That is a good point, and generally they want as many paths/redundancies as possible. The DoD has its own molniya orbit satellites, quite recently launched, but capacity is limited.