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Doesn't really answer the question of why does the military use the L-band. Whether it's jammed or not is immaterial (of course they are going to jam it if it h

by 4ad 1y ago

Doesn't really answer the question of why does the military use the L-band. Whether it's jammed or not is immaterial (of course they are going to jam it if it has military use), but what specific attributes makes L-band useful for the military?

echoangle 1y ago
If I understand the article correctly, the actually used frequencies are close to the L-band but the jamming is broadband and also affects the L-band.
- myself248 1y ago
  The L-band is a term for the whole swath between 1 and 2 GHz. It's diced into dozens of allocations by international treaty. Some ranges are set aside for GPS/GNSS: https://gssc.esa.int/navipedia/index.php?title=GNSS_signal https://gssc.esa.int/navipedia/index.php?title=GNSS_signal Some are monitored by the SMAP satellite: https://en.wikipedia.org/wiki/Soil_Moisture_Active_Passive https://en.wikipedia.org/wiki/Soil_Moisture_Active_Passive (Also in the L-band are all sorts of other things. A lot of cellular bands, known in the US as PCS and AWS, and more. Several different sat-phone systems. ADSB in 1090 is juuuust inside L-band. And more...) All transmitters produce a bit of out-of-band interference, beyond where they meant to transmit. This is filtered to reduce it to a certain level below the intentional frequency, but filters aren't perfect. So when someone tries to jam GPS or other services, they inevitably bleed some energy into neighboring allocations too, some of which seems to be being picked up by SMAP. Note that SMAP's passive radiometer doesn't have pinpoint spatial resolution, 36km is stated. This means it's listening to a pretty significant patch of ground at any given time, so for a source to be picked up among all that, it's got to be pretty loud. It also means that attributing the source is limited in precision, you can get to city level but not city-block level from this data.
  - touisteur 1y ago
    Yes, civilian radarstuff (Mode S, SSR, ADS-B as you said, and other multilateration schemes) use 1090 (downlink and broadcast) and 1030 MHz (uplink). Closer to military uses, IFF might also use the same frequencies.
cebert 1y ago
L-band is capable of long range with lower power and can penetrate water and foliage. I can see why this could be appealing for military purposes.
- bc569a80a344f9c 1y ago
  To expand a little bit, RF is subject to free space path loss - signal strength decreases proportional to the square of the frequency and the square of the distance. The higher the frequency, the less far you go. Of course, weaker signals are harder to distinguish from noise so there’s only so weak your signal can go. If you want to control drones, lower frequencies are better. There’s a reason that microwaves (the cooking instrument, named after the rough band of RF frequencies it uses) interfere with WiFi when improperly shielded: they run at approximately 2.4GHz. That’s a part of the band that’s free to use without licensing (ISM band, runs at 900MHz, 2.4GHz, 5Ghz, and so on). That’s because microwave manufacturers don’t want to license spectrum, and it’s the part of the ISM band closest to the ideal absorption frequency of water. The point of microwaves is to push energy into water molecules and make them move around faster, aka heat them. Water molecules do that well at 2.4GHz. This also means that water blocks RF at that frequency very well, because it absorbs it. Trying to shoot 2.4GHz WiFi through trees sucks because it gets blocked by the leaves. So you want to control drones. You can’t be around 2.4GHz because rain would screw you up. You can’t go above that so you can get enough distance. You can’t go as low as 900MHz or other stuff on the ISM band might interfere with you. Not that much left, given that 1.7GHz is a popular cell phone frequency, and so on - you can look at publicly available frequency charts to see what’s assigned for what where. This glosses over a lot and is heavily simplified.
  - ratatoskrt 1y ago
    There is no absorption peak of water at 2.4GHz. Even worse, the absorption spectrum will change when it heats up.
  - immibis 1y ago
    AFAIK the ISM band was placed there because of microwave ovens, not the other way around.
TrackerFF 1y ago
Navigation systems (GNSS) tend to fall right in the L-band. For example, the Russian GLONASS is in the 1.2 and 1.6 GHz range, while GPS is around 1.1, 1.2, 1.5 GHz. SMAP is in the 1.2 - 1.4 GHz range - so it overlaps with both GLONASS and GPS. So jamming in that range will affect the nav systems of the drones. This is the reason you see drones tethered with fiber optic cables - control systems might be in the same range. The "why" has more to do that the machines are made to adapt to existing systems, and those systems were designed due to the physical properties they've made to serve / solve. Both jamming and spoofing is pretty normal when you're close to Russia. And this is the reason SMAP will pick up all this jamming, because it is sensing on the same band / range.
sandos 1y ago
I mean, in a drone way every frequency is usable. If its not that usable, it might still be usable if nobody knows you are using it yet, and therefor not jamming it yet.

by 4ad 1y ago

echoangle 1y ago

If I understand the article correctly, the actually used frequencies are close to the L-band but the jamming is broadband and also affects the L-band.

myself248 1y ago
The L-band is a term for the whole swath between 1 and 2 GHz. It's diced into dozens of allocations by international treaty. Some ranges are set aside for GPS/GNSS: https://gssc.esa.int/navipedia/index.php?title=GNSS_signal https://gssc.esa.int/navipedia/index.php?title=GNSS_signal Some are monitored by the SMAP satellite: https://en.wikipedia.org/wiki/Soil_Moisture_Active_Passive https://en.wikipedia.org/wiki/Soil_Moisture_Active_Passive (Also in the L-band are all sorts of other things. A lot of cellular bands, known in the US as PCS and AWS, and more. Several different sat-phone systems. ADSB in 1090 is juuuust inside L-band. And more...) All transmitters produce a bit of out-of-band interference, beyond where they meant to transmit. This is filtered to reduce it to a certain level below the intentional frequency, but filters aren't perfect. So when someone tries to jam GPS or other services, they inevitably bleed some energy into neighboring allocations too, some of which seems to be being picked up by SMAP. Note that SMAP's passive radiometer doesn't have pinpoint spatial resolution, 36km is stated. This means it's listening to a pretty significant patch of ground at any given time, so for a source to be picked up among all that, it's got to be pretty loud. It also means that attributing the source is limited in precision, you can get to city level but not city-block level from this data.
- touisteur 1y ago
  Yes, civilian radarstuff (Mode S, SSR, ADS-B as you said, and other multilateration schemes) use 1090 (downlink and broadcast) and 1030 MHz (uplink). Closer to military uses, IFF might also use the same frequencies.

cebert 1y ago

L-band is capable of long range with lower power and can penetrate water and foliage. I can see why this could be appealing for military purposes.

bc569a80a344f9c 1y ago
To expand a little bit, RF is subject to free space path loss - signal strength decreases proportional to the square of the frequency and the square of the distance. The higher the frequency, the less far you go. Of course, weaker signals are harder to distinguish from noise so there’s only so weak your signal can go. If you want to control drones, lower frequencies are better. There’s a reason that microwaves (the cooking instrument, named after the rough band of RF frequencies it uses) interfere with WiFi when improperly shielded: they run at approximately 2.4GHz. That’s a part of the band that’s free to use without licensing (ISM band, runs at 900MHz, 2.4GHz, 5Ghz, and so on). That’s because microwave manufacturers don’t want to license spectrum, and it’s the part of the ISM band closest to the ideal absorption frequency of water. The point of microwaves is to push energy into water molecules and make them move around faster, aka heat them. Water molecules do that well at 2.4GHz. This also means that water blocks RF at that frequency very well, because it absorbs it. Trying to shoot 2.4GHz WiFi through trees sucks because it gets blocked by the leaves. So you want to control drones. You can’t be around 2.4GHz because rain would screw you up. You can’t go above that so you can get enough distance. You can’t go as low as 900MHz or other stuff on the ISM band might interfere with you. Not that much left, given that 1.7GHz is a popular cell phone frequency, and so on - you can look at publicly available frequency charts to see what’s assigned for what where. This glosses over a lot and is heavily simplified.
- ratatoskrt 1y ago
  There is no absorption peak of water at 2.4GHz. Even worse, the absorption spectrum will change when it heats up.
- immibis 1y ago
  AFAIK the ISM band was placed there because of microwave ovens, not the other way around.

TrackerFF 1y ago

Navigation systems (GNSS) tend to fall right in the L-band. For example, the Russian GLONASS is in the 1.2 and 1.6 GHz range, while GPS is around 1.1, 1.2, 1.5 GHz. SMAP is in the 1.2 - 1.4 GHz range - so it overlaps with both GLONASS and GPS. So jamming in that range will affect the nav systems of the drones. This is the reason you see drones tethered with fiber optic cables - control systems might be in the same range. The "why" has more to do that the machines are made to adapt to existing systems, and those systems were designed due to the physical properties they've made to serve / solve. Both jamming and spoofing is pretty normal when you're close to Russia. And this is the reason SMAP will pick up all this jamming, because it is sensing on the same band / range.

sandos 1y ago

I mean, in a drone way every frequency is usable. If its not that usable, it might still be usable if nobody knows you are using it yet, and therefor not jamming it yet.