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

http://www.bbc.co.uk/h2g2/guide/a588684

An overview of the basic concept of radar.

Very good entry. Informative, factual, the sort of stuff for the guide. IMO it is good already.

Just in case you might want to consider:

What is the range of a radar? Or, mor generally, could you add some typical specs of radars (i.e. frequencies, ranges, powers)? What about flying 'under' the radar? How does that happen. Can a Radar see behind a mountain?

The specs could be easily added, since they would not conflict with the contents of the entry.

Thanks for your valuable attention,


HELL

Oh and is it 'high jacking' or 'hijacking'?

Cheers,

HELL

By the way - you see, I should concentrate all thoughts first, sorry if that annoys you - another thing came to my mind:

Is GPS pushing radars aside? I mean: An aircraft (or ship or whatever) equipped with a GPS could just transmit all sorts of data to a ground station, without needing a radar. Radars would then just be used as a secondary-safety-redundancy-systems. Are radars becoming obsolete? Are there other alternatives?

Oh: These questions are just out of pure curiosity - The entry is OK the way it is.

Thanks,

HELL

I'm only a weekend sailor, but I would say that GPS and RADAR complement each other. A standard GPS only tells you where you are. With a chart (real paper or digital) you can then find out what fixed hazards are around you. But only RADAR will tell you there's a tanker out there in the fog

Are there two varieties of transponder for civilian and military?

Nice entry, and the comments already made are what I thought of too. And it is fine the way it is, but do you have any info on "masking" your radar signature (or whatever it would be called)?

Thanks for your comments. Range varies so much on height of radar station, height of aircraft, transmitter powers, and receiver sensitivities, ground obstructions etc that I didn’t really want to confuse the issue.

I could include frequencies if you think people would be interested,(Ididn't want to get too technical) and on flying under radar, only I don’t seem to be able to edit it now, so I can’t even correct the high jacking error. This is the first piece I have submitted to peer review, am I missing a trick?

As regards GPS although very useful it won’t replace primary radar as you can’t rely on all aircraft and ships transmitting their position all the time. Primary radar will detect aircraft (or ships) that are not equipped with transponders or have turned of for what ever reason and particularly in the case of ships will also detect the shoreline in fog or at night. It’s not a good idea to have all aircraft transmitting their GPS data all the time as signals would interfere with each over. Transponder only reply when the interrogation beam is pointing directly at them. Also people could deliberately transmit false data for whatever reason. GPS information could be coded into the replies (in the future) which may provide greater detail, but I think this is beyond the scope of this posting.

Thanks for your comments. Range varies so much on height of radar station, height of aircraft, transmitter powers, and receiver sensitivities, ground obstructions etc that I didn’t really want to confuse the issue.

I could include frequencies if you think people would be interested,(Ididn't want to get too technical) and on flying under radar, only I don’t seem to be able to edit it now, so I can’t even correct the high jacking error. This is the first piece I have submitted to peer review, am I missing a trick?

As regards GPS although very useful it won’t replace primary radar as you can’t rely on all aircraft and ships transmitting their position all the time. Primary radar will detect aircraft (or ships) that are not equipped with transponders or have turned of for what ever reason and particularly in the case of ships will also detect the shoreline in fog or at night. It’s not a good idea to have all aircraft transmitting their GPS data all the time as signals would interfere with each over. Transponder only reply when the interrogation beam is pointing directly at them. Also people could deliberately transmit false data for whatever reason. GPS information could be coded into the replies (in the future) which may provide greater detail, but I think this is beyond the scope of this posting.

This is an excellent entry in my opinion. Short but full of info with no waffle. Excellent.
My one question is that I've heard that one can actually image things with RADAR these days - I seem to remember a Tomorrow's World where they imaged The Clock Tower of Westminster Palace doing this. Should this be included or is this still in the realms of research?

Yes, Ausnahmsweise, there are two type of transponder civil and military, but they both work in exactly the same way. The military transponder does all the thing a civil transponder does but also has some extra modes for doing military only stuff.

Sorry Orcus I must of missed that Tomorrow's World. I don't know anything about it.

Editing ability mysteriously returned. Flying under radar added and hijacking corrected.

Thanks. I thought I had heard that, in connection with the shooting down of the Korean passenger jet. I think Bitish troop transport jets actually reply with both signatures.

But we digress. It's always hard to know where to stop with an entry. I think yours is just fine as is.

Awu.

It's pretty rare lately that I get to scout an article on a subject I know much about. Whether you see this as a good thing or a bad thing, we'll have to see...

I don't think this article is very close to completion. For one thing, it leaves out all military applications. Radar was invented for the military, and is still its main user. Weather applications are also worth discussing.

I think we need a discussion of pulsed radars vs. continuous wave (ex. Doppler), search radars vs. tracking radars, and ordinary antennas vs. phased array. I think we could also use a bit of history, just discussing how they came about in WWII, and how they transformed warfare. I think this article should also discuss ECM and ECCM (electronic countermeasures and counter-countermeasures). I think these areas should be covered with brevity, just enough to give the reader a taste. They could all be discussed to greater length in seperate articles.

I would be happy to help out with any content in these areas, since I could reasonably knock out most of it off the top of my head.

BTW... to correct a misconception in this forum... pulse repetition frequency (in a pulsed radar, obviously), transmit power, receiver sensitivity, and reflectivity of the target are the only real factors for a radar's range. Radar height just affects how far it can see along the horizon.

And speaking of radar horizon, that's what you're flying under when you "fly under" radar. Radar beams travel in straight lines, but the earth is curved, so you can only see so far... about 24,000 ft at ground level, if I recall. You can see a bit further if you build your radar tower higher. Something flying at high altitude can be spotted coming up over the horizon at a significantly further range. If you're trying to avoid radar, you would fly at the lowest altitude possible, to delay breaking across the radar horizon until the last possible moment. But you really can't avoid crossing over it. Hollywood has spread the myth that you can avoid radar completely, but it's just that... a myth. Not even stealth planes *avoid* radar... they just reflect such a small amount that it is difficult to recognize outside of the signal noise.

Looks like it's a good thing I have a vague understanding of some of the things you mention (connections with Naval Air Dept. in an earlier life) but I didn't realize until you mentioned them that they were missing from the entry.

How much of the history do you know? Is it true that some young amateur (school boy) suggested the principal, but since the military was alaready researching it they couldn't credit him with the idea?

Doh! You had to call me on the history part, didn't you?

When I said I could knock off *most* of this off the top of my head, it was the history in particular that I was excluding. All I know is that the first radar stations came into use on the British Isles, and were invaluable for the air defense in WWII of Britain, and that their use on the high seas transformed naval engagements (although not as much as the aircraft carrier).

Sir Kitt, I'm also fairly acquainted with the subject matter, and had plans to make a **h2g2 University Project** about Radar. You're quite new to h2g2 and may not have seen the University yet.

Could I have your opinion about it, I mean, joining forces and making a set of some 8 to 10 entries about history, LPRF/HPRF/CW radar, the range equation, ECM/ECCM etc. ?

The University is at http://www.bbc.co.uk/h2g2/guide/C573

hee hee, how about you join as well, Colonel ?

BTW, in 1904 some Christian Hülsmeyer got the first patent on Radar

I'd be willing to knock out a few entries on the subject. I'm not worried about this getting in the way of my current Uni project, because unlike that one, I wouldn't have to research this one too much.

While we're kicking around ideas about a RADAR university project, would you care for information on the police use of radar?