I read a lot about passive radars trying to leech off of opportunistic waves, and lots about actual troops preferring to play hide-and-seem with anti-radiation weapons just to use active machines.
A config that strikes me as obvious but doesn’t seem to be popular would be just bistatic where you fire your own transmitter far away from yourself?
There’s got to be a reason, but it seems like best of both worlds.
Multistatic radars (of which bistatic are just the case with N=2) are like the nuclear fusion of radar systems: everybody agrees it would be neat to have them, but they're always 20-30 years in the future. In practice it is extremely difficult to maintain the precise timing synchronization required for radar systems. Especially when used in moving vehicles or in sparsely populated areas the expected error goes WAY up to the point of unusability.
The survivability gains are also overhyped since 1. the enemy can just blow up the transmitters leaving you with a bunch of useless receivers and 2. most air defense doctrines already treat radars as something that should be distributed widely, so you can lose a few without the whole system collapsing.
The article goes into this only briefly, but modern radar systems don't just send out any random pulse but they very specifically tailor the waveform going out in order to do cool signal processing tricks like pulse compression. There is also the matter of frequency. The lower the frequency, the bigger the antenna you would need to get a proper direction reading out of it. Fire control radars typically operate in the X-band, around 10 GHz. Most civilian radio transmitters are around 100 MHz, so you'd need impractically large antennas and even then the bandwidth limitations would severely limit spatial resolution. One saving grace here is that stealth airplanes are typically most highly optimized against X-band radars from the direction they're going to bomb (forward), so you might have a better chance with a normal system, but then you still might not have a precise enough target to actually shoot at.
So while the multistatic system does offer some advantages, in practice it's just cheaper and (importantly for military use) requires less fiddly bits in the field to just use normal monostatic radars. Civilian use also doesn't benefit greatly from being multistatic. It's a bit like Tesla turbines or hyperloops: cool idea and it even "works" in a way, but the normal way of doing things is just way better when budgets and engineering realities come into play.
Source: I was a radar engineering officer in the Dutch navy about a decade back.
One reason is Low Probability of Intercept radars (and transmitters / datalinks) do exist, and are very difficult (but not impossible) to identify and locate.
Probably more complicated to setup in a hostile environment because you'd need multiple transmitters, which also need to remain stationary, or at least you need to accurately know when they move.
Knowing where the transmitters are is vital. So wonder if you build in a positioning system to them. Each transmitter transmits a signal, but also rebroadcasts the signals it receives from the other transmitters on separate bands (these can be at lower power). If you can pick up a few transmitters, is that enough to build a model of where they are relative to each other, and then where they are relative to you?
If each transmitter picks up the rebroadcasts if its own signals, then with some assumptions about the rebroadcast lag (or measurements of it added to the signal!), that's enough to know the range to each other transmitter, right? So maybe they do that and then just broadcast the ranges (tagged on to their main signal), then any remote receiver can work it all out from there.
> that's enough to know the range to each other transmitter, right?
Only in a flat environment without too much atmospheric distortions. As soon as you get multipath effects from eg waves bouncing off buildings and mountains then the computational complexity goes through the roof. Also I don't think you should underestimate how much the signal degrades in a "target path" vs the "direct path". The article mentions -60 dB and I think that is fairly optimistic. The transmitter power needs to be HUGE to make it work, so it would be much easier to have stationary transmitters. Normal radars manage to do this because they are highly directional, but multistatic radars need to look in all directions at once and need to up the power as a result.
We should run electric third rail along the Mississippi. It’s already barges with tugs so a few electric tugboats mostly running during daylight hours, we could electrify most of this by just replacing a few tugboats. Make the lines high capacity enough to run along the coasts, and a fleet of tugs could be a huge dispatchable load, slow steaming could free up a lot, and going just a few kts faster would mop up a ton of what may be otherwise curtailed
Tugs could afford the weight of a bunch of even lead-acid batteries and go electric without the need for a huge amount of infrastructure going the entire length of the Mississippi.
Yes, but even with my worst handwriting, in situations where I and l matters, I can always choose to do an especially I I or particularly l l even if most are indistinguishable which a font can not do
I can see how you'd do an especially I I. You just need to include the serifs, which I always do in handwriting anyway.
But how do you emphasize a lowercase 'l'? The only method I know is to make it cursive, which looks terrible.
(I don't really need to distinguish l from I, because I put serifs on I. But I do sometimes need to distinguish it from 1; in natural writing, 1 and l are identical.)
Transmission in this sense does not include distribution losses (by the DNOs, at lower voltages). 8% in your link.
The UK government is now touting datacentre sites with better access to the national grid (transmission network) to avoid the issues inherent in the distribution networks. E.g. Culham which had a grid connection to power the JET fusion experiments.
I have found daily-driving Ubuntu at Delft shocking pleasant. Chrome, zotero, obsidian, zoom, and so on all work great. Outlook, teams, and the office suite, and signing pdfs are all the sharpest edges by far.
I feel if the TUs were required to dogfood this, especially if generously funded such that startups could come along and provide the same service and support, that it could be a great positive externality
My university uses Teams and the browser version is missing some features. For example, I can't see the files uploaded by the professor. That tab won't load.
PDF signing is the bane of my existence, luckily I can get by with a cloud solution but it's nowhere near how easy I wish it would be. Sadly I'm still forced to use a Windows VM or dual-boot because the tax authority in my country requires a root/digital certificate for login to their web system, at least for incorporated entities.
I can find a dozen solutions to sign a PDF on linux without much trouble. Now redacting seems a whole nother story.
I've failed to find even a single option on linux that does real PDF redaction like adobe acrobat. Most don't do redaction at all or worse they say they redact but it's actually just black highlighter on black text or some other kind of overlay that leaves the underlying text data intact.
Thanks for the tip, it might work if I can figure out where the certificate is stored on Windows because I am forced to go through an application first.
The original sin was using watts not joules. Humans hear watts as “gallons” and “watt hours” as “gallons per hour” and all the rest of this confusion in every article about EVs/fast chargers/distribution/solar/everything all trace back to “X-Hours” and “X” incorrectly sounding like a rate and a count, not a count and a rate.
A config that strikes me as obvious but doesn’t seem to be popular would be just bistatic where you fire your own transmitter far away from yourself?
There’s got to be a reason, but it seems like best of both worlds.
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