h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Interesting - but does seem a little too 'random' be of much practical use...

Could you really use software to deal with such a random event - especially as you'd need detailed data on the air temperatures/humidities for the whole distance between you and your target to compensate for the distortion - otherwise the target would just be showing up in the wrong place.

Plus of course, if your radar's just upped it's range by several hundred percent off its own back using a temporary natural meteorological phenomenon, you're probably going to exceed the thing's MTUR (PRFxC/2) and it's going to be a heck of a job trying to figure out just where your target is...

"Skipper - we've got a target on radar - he's either at 100, 200, 400, 800 or 1600 miles away - we can't be sure which"

I guess it'd be used for early warning, in a similar way to ESM, rather than target location. Or perhaps it is one of those new-fangled phased array thingies, with variable PRFs and no restrictions on sweep. It could probably tell quite easily which pulse was being returned.

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If we're still talking naval comms, I find this very surprising. Inverse square laws, diminishing returns and all that; there are much more efficient ways of talking over long distances nowadays, ways that don't require an entire generator or that turn the whole upper deck into a no-go area. Radars do it for very brief periods, yeah, but a radio? Or were you talking about the engines?

Traveller in Time measuring cellular phones
"Burst transmission is just what mobile phones use, there is not a generator deck in your backpocket.
Another reason why the radiation is not heating anything, any object is cooled down before the next burst comes out. "

Burst or no burst, if the cooling down process takes place on a timescale of seconds or longer, if the repetition rate of burst is even a few Hz, the average power is all that's really important in terms of general heating, unless burst strength/duration is such that a single burst can cause a significant immediate rise in temperature, which doesn't seem likely.

In my case, with my old phone, I only know I got a localised headache from extended use, that using the phone consistently on one or other ear would result in an appropriately-located headache, and that the effect was consistent enough to prompt me to minimise phone use even more than I would otherwise have done.
It wasn't something that actually worried me, not least since I used a mobile far less than most people I knew. I just didn't like the effect.

I don't know which bit of anatomy was causing the headache. It is said there aren't any pain receptors in the brain itself, though how that squares with headaches/migraines, I'm not sure.
For all I know, any effect could have been in the skull or one of its attached membranes. If bone *is* a good absorber of microwaves at mobile phone frequencies, then presumably a small region of the skull could heat a little.

"If we're still talking naval comms, I find this very surprising. Inverse square laws, diminishing returns and all that; there are much more efficient ways of talking over long distances nowadays, ways that don't require an entire generator or that turn the whole upper deck into a no-go area. Radars do it for very brief periods, yeah, but a radio? Or were you talking about the engines? winkeye"

Yup, but this was back in the days when only a small percentage of ships had secure satcom - so we tended to use MF/HF for everything, and if you're re-transmitting a constant broadcast channel from one ship to others in the same area, the transmitters on the go all the time (This was back in the good old days of Frequency Shift Keying Teletypes running at 75 Baud)

The good old fashioned days of radio communications - when it was a dark art trying to keep in contact with your home from half way around the world, selecting frequencies that'd bounce, manually tuning receivers to get the most out of a very dodgy incoming signal... Nowadays its just a) Point the dish at the right satellite and b) Press send.

Was referring to Blathers' megawatt quote rather than your hundreds of watts, but yeah, I guess things used to be a bit different. I've worked on new stuff that has to be able to support the old teletypes at 50 baud - believe it or not - it's damned hard finding anything that'll work that slowly nowadays.

"there is not a generator deck in your backpocket."

Speak for yourself.

Is that a generator deck in your pocket or are you just pleased to see me?

I'm always pleased to see you Whisky.
















Please note new tagline.

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There would be some unreliability, I can imagine. But assuming the target is an inbound threat, at some point you're going to establish contact with him that isn't dependent on ducting. At that point it'll probably appear to jump to another location, but that's at the point where, pre-ducting technology, you would have first picked up the track. You're already started in your evaluation of the track by then, giving you crucial time to respond. If you're attempting to engage a target that isn't inbound and is beyond normal LOS radar range, you could use the radar to get the missile into the general area, then turn it over to the missile for terminal homing.

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Two words: phased array. You're talking about a limit faced by rotating antennas. If your antenna is fixed and you're sending your signals out of multiple emitters, your MTUR is greatly expanded. An emitter transmits a pulse, then the emitter next to it transmits one, and so on. Any particular emitter is free to listen until its turn to participate in the sweep comes up next.

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Whisky is talking naval comms. I'm not. As I mentioned before, my specialty was fire control. "Reach out and touch someone" meant something very different in my field.

"I'm not. As I mentioned before, my specialty was fire control. "Reach out and touch someone" meant something very different in my field."

That's true - There's an old joke about the radars on Aegis cruisers - you don't have to shoot down incoming planes, just point the radar on them and turn up the juice and you'll cook the pilot. (The original version was _far_ less polite )

As to phased arrays - my knowledge of radars is limited to 1980s Soviet setups - they weren't that hot on high-tech, so I'll take your word on that!

On a more serious note though - the one downside to that is of course that their ESM gear is going to pick you up far sooner - so it's rather a two edged sword... Maybe that's why it's not been done - at extended ranges it might well be better to _not_ have your radar burning and turning and to rely on a possibly less accurate ESM fix to get your missile into the rough area of an incoming target.

(Have we gone ever so slightly off topic?)

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I never saw it myself, but I'd heard lots of sea stories of seagulls getting too close to the transmitters, and erupting into a puff of feathers.

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But assuming you're searching anyway, that ducted dwell is going to be picked up by the enemy ESM gear regardless. You might as well get some intelligence back in return.

ESM alone isn't going to be nearly accurate enough to get a missile in the area. For one thing, unless you can share tactical data with another ship and triangulate, you're not going to have a range.

I did participate in an extremely interesting and hilarious wargame in which the opposing fleets "stealthed" themselves by shutting down all the active EM systems, but I'm not sure I'm not allowed to share the anecdote. I can say that it took one idiot electronics technician to turn on the air search radar on the enemy carrier for five minutes as part of a normal maintenance procedure to doom them.

"ESM alone isn't going to be nearly accurate enough to get a missile in the area. For one thing, unless you can share tactical data with another ship and triangulate, you're not going to have a range."

It can be done - either you risk your own satcoms - which _should_ be on a narrow enough beam to avoid being DF'ed or you take your own bearings from your ship and combine them with bearings from shore stations (you don't have to EMCON a shore-based sigint station - everyone knows where they are already.

It's certainly accurate enough for SSMs (Harpoon etc.) - not sure if you could use it to launch long-range SAMs though.

Traveller in Time giving up
"I am not going to carry an antenna array on my head and throw my mobile in the direction of an incoming message ! "

Well, Harpoons are an entity all their own. They're basically fire-and-forget weapons who will go into their own search mode. It's something a Harpoon can afford to do, because their targets are going to be large, slow, ungainly things. Theoretically you could conduct the whole exercise without breaking EMCON, since a Pentagon satellite operator could pinpoint the target by observing its wake, and transmit the coordinates to the firing ship.

SAMs need to be as fast as they can be, to give them an opportunity to hit a fast, nimble target before it can maneuver out of the way. They also need to be slim to avoid detection. That only leaves you with a limited amount of rocket fuel, so active search is not something they can afford to do. They've got to be pointed at the target the instant they leave the silo.

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A GSM phone, like all radio transmitters, will transmit using maximum bandwidth until it has transmitted all its data. Sporadic usage patterns are not the same as burst transmissions.