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GL Mk. I radar

GL Mk. I radar (edit | talk | history | links | watch | logs)

• Featured article candidates/GL Mk. I radar/archive1

Nominator(s): Maury Markowitz (talk) 19:55, 10 December 2024 (UTC)

This article is about a British radar system that aided the Army's anti-aircraft gunners. I think it's interesting because it was so low-tech that it helped convince the Germans that British radars were not very good (along with the similar MRU, an article I'll get to) and the amusing bit about it causing a nationwide shortage of chicken wire.

The article went through A-class some time ago, and it looks like I'll have some time to work it over the holidays, so here goes... Maury Markowitz (talk) 19:55, 10 December 2024 (UTC)

Image review

• Suggest adding alt text

• Don't use fixed px size

• Why are there two of File:GL_Mk._II_radar_transmitter.jpg?

• File:GL_Mk._II_radar_transmitter.jpg: source link is dead

• File:GL_Mk_IIIc_radar_Accurate_Position_Finder.jpg needs a US tag. Nikkimaria (talk) 05:47, 11 December 2024 (UTC)

@Nikkimaria: Queries: (1) what should I use instead of fixed px sizes? (2) should I use an archive URL for the dead link, or find another page with the same image? (3) There are two copies of the one image simply because we needed one to be in the lede for the DYK - I'm trolling the web looking for one to replace it at the bottom. (4) Canadian pic, what do I need in this case, a second tag for the US as well? Maury Markowitz (talk) 16:56, 11 December 2024 (UTC)

(1) |upright=. (2) Either, as long as the latter would verify the information provided on the description page. (3) If no other image can be found, the duplicate should be removed, DYK or no. (4) Commons requires images to be free in both the US and their country of origin. Nikkimaria (talk) 00:26, 12 December 2024 (UTC)

Ok all fixed. Maury Markowitz (talk) 00:37, 13 December 2024 (UTC)

It doesn't look like the dead source link has changed? Where and when was File:GL_Mk_IIIc_radar_Accurate_Position_Finder.jpg first published? Nikkimaria (talk) 04:38, 13 December 2024 (UTC)

Ok, it seems to have saved the new URL this time, not sure what I did. The second was first published in 1942/3. Maury Markowitz (talk) 16:24, 13 December 2024 (UTC)

Where? Nikkimaria (talk) 04:32, 14 December 2024 (UTC)

NRC lab reports, Ottawa. They would have been available in the UK and US at the same time, and likely other Commonwhelth nations but I can't confirm that. The original image is now in the archives in Waterloo. Maury Markowitz (talk) 14:56, 14 December 2024 (UTC)

Sorry, to clarify, which part of that cannot be confirmed, and what do you mean by "available"? Nikkimaria (talk) 15:41, 14 December 2024 (UTC)

I cannot confirm it was available in other commonwealth nations in the radar circles - namely Australia, NZ and South Africa, but I assume they did. The UK definitely got it, it's in Kew. By "available", the parties to the arrangement, which included at least the UK, US and Canada, sent copies of their research documents to the other parties when they were published. So in this case it would have arrived at the radlab within days of it being published in Canada. Maury Markowitz (talk) 15:12, 19 December 2024 (UTC)

Looking on Commons, it seems that there is a perfectly good alternative here, the Mk. IIIB image. Is this one perhaps more useful? Do UK images in PD also require a US tag? If so, would this one be easier to verify? Maury Markowitz (talk) 13:33, 20 December 2024 (UTC)

Comments from Graham Beards

• "Plans to introduce the Mk. II with accurate bearing and elevation were underway from the start" From the start of what?
• "1,679 Mk. IIs were ultimately produced." Can we avoid starting this sentence with numerals?
• "The GL effort was started very early during CH development, and like CH of that era, used relatively long wavelengths as these could be generated and detected easily using existing electronics from commercial shortwave radio systems". The lay reader might wonder how long wavelengths can be obtained with shortwave radios.
• "The antenna was only marginally directional, with the signal being sent out in a wide fan about 60 degrees on either side." There is a fused participle here. How about "and the signal was sent out in a wide fan about 60 degrees on either side." Or just drop the "with"?
• "A more serious limitation was the displays themselves" I think "themselves" is redundant.
• "As Mk. I arrived in the field, a number of improvements in the basic electronics were introduced." Perhaps "several improvements"?
• "To better study the AA problem" Are you happy with the split infinitive?
• "The separate range and bearing receiver units could operate on a number of frequency bands" Several ?
• "A common oscillator was used by both receivers, which was sent into the four-tube radio frequency (RF) section" Perhaps provide a link to Electronic oscillator?

That's it from me for now. Graham Beards (talk) 17:00, 14 December 2024 (UTC)

All of these are updated. Thanks! Maury Markowitz (talk) 16:32, 19 December 2024 (UTC)

Comments from Mike Christie

I've copyedited a bit; revert anything you disagree with.

• "which provided both mobile early-warning service, as well as relocatable service in case a main CH station was knocked out". You don't need both "both" and "as well as"; either "both mobile early-warning service and relocatable service" or "mobile early-warning service, as well as relocatable service" would work. But it took me a second to understand the point of "relocatable". How about "which provided mobile early-warning service, and could also be relocated to replace a main CH station if one was knocked out"?
• I don't think any change is needed, but I'm curious as to how accuracy was measured. If the radar was accurate to 25 yds for an aircraft several miles away, how was this determined? Even at slow speeds an aircraft would cover that distance in less than a second, so any form of human-triggered measurement seems unlikely to be precise enough. Could tests be done against objects on the ground?
• "and produce a null on the display": what is a null? I understand the concept, but does this just mean that the display would be blank? And I see the word is used later in the article; it appears the display is not blank so I am unclear what is meant.
• I see there's an article on GL Mk. III radar, but not on GL Mk. II radar. If the Mk. II is covered in this article, shouldn't the title reflect that?
• "by sliding a copper ring along post on the core": presumably this should read "along a post"?
• I don't think we need the wikilink to ladder, unless you intended that to go to some technical article with a similar name.
• "Images exist that show both antennas combined on a single cabin": why is this worth mentioning? Surely images exist of many of these devices and their installations.
• For note c I think you need a source for the suggested explanations. Without one I think it would be best to cut the note.

I don't know enough about electronics to provide any subject matter feedback on the description section, and I struggled to understand some of it, but that's the nature of technical articles. I think the article does what it can reasonably do towards explaining the material as simply as possible. Mike Christie (talk - contribs - library) 19:58, 15 December 2024 (UTC)

All updated. Some notes:

• The accuracy was a function of the pulse width. Back then you could only be sure the target was within the distance that the pulse covered at the speed of light. So you want as short a pulse as possible to get better range accuracy. But there's limits to how short you could get with their electronics and still have a solid signal. Today they use various tricks like pulse compression that allow you to use long pulses and then compress them on reception and ~1m is not an issue.
• I hear you on the title? I didn't like "Mk. I and Mk. II". For the AI radar I went with Mk. IV, as the vast majority were Mk. IV sets, but in this case it really is more mixed. But also two articles seemed wrong too. Suggestions?

• I have no idea who linked ladder!
• I trimmed C, but still worth mentioning that the sources don't say I think.

Maury Markowitz (talk) 16:39, 19 December 2024 (UTC)

For the title, maybe Early GL radar? Or failing that, GL Mk. I and Mk. II radar is at least accurate, if a bit clumsy. Whatever you pick, don't move the article till the FAC concludes as that would screw up the bot that handles closes. Looks like you skipped my second-to-last question? All your other responses look fine. I expect to support but would like to read through again first; please ping me once the other reviewers' comments are resolved. Mike Christie (talk - contribs - library) 20:36, 19 December 2024 (UTC)

Yeah, I agree this needs a better title. Early British radar systems perhaps? RoySmith (talk) 22:06, 19 December 2024 (UTC)

But this is one of several designs that would fall under that title. CH and MRU definitely do! I think Mike's second one works? Maury Markowitz (talk) 13:35, 20 December 2024 (UTC)

I did miss that one point. The issue here is that both Mk. I and Mk. II used two separate cabins for transmitter and receiver, but there are photographs showing both on a single cabin. There's really little information beyond that, but it seemed worth mentioning. Maury Markowitz (talk) 13:36, 20 December 2024 (UTC)

RoySmith

I'm reading through this now. So far, looks pretty good. Note that I'm not into milhist; I approaching this from the engineering standpoint.

Development

• The first mention of radar in the UK was ... Do we really have a solid source for there being no earlier mentions? See User:RoySmith/essays/First is worst.
  • Still needs to be addressed.
• The GL effort was started very early during CH development, and like CH of that era, used relatively long wavelengths as these could be generated and detected easily using existing electronics from commercial shortwave radio systems I stumbled when reading this, because I remembered reading earlier about 600 MHz being used and didn't think there was any 600 MHz gear in commercial use back then. When I went back I saw that the 600 MHz was a different unit, but you might eliminate this confusion by saying up front something like "Despite Butement's earlier experiments with 50 cm technology, the CL used relatively long 50 meter wavelengths as these could be generated ..."
• antennas on the order of 25 m perhaps link to half-wave dipole here.
• Clearly, this was not practical is that you doing the editorializing ("clearly"), or does the source say that?
• produce a smoothly varying voltage, does the source say "smooth"? I assume "linear" would be a better word, or more likely Sawtooth wave.
• sent into the CRT's other channel, typically the Y-axis It took me a little bit to understand what you're getting at here, mostly because my familiarity with modern radar sets had me assuming it would be using a Plan position indicator, which these early radar sets didn't. It might be useful to mention that this is known as an A-scope display, and perhaps use the illustration at Radar display#A-Scope.
• For this role, the system used two receiver antennas mounted about one wavelength apart I'm having trouble visualizing this. One wavelength apart in what direction? Normal to the azimuth? Vertical? Horizontal? Drawing a diagram would help here.
• The transmitter, which had a power of about 20 kW is that 20 kW average continuous power, or peak power? I suspect the latter, but the source should say.
• Three antennas were mounted in a line down one of the long sides of the framework again, a diagram would be really helpful here.
• Behind the two bearing antennas were reflectors mounted about a wavelength away, which had the effect of narrowing their reception angle that sounds like you're describing a yagi. If so, link to that.
• it provided very accurate range measurements on the order of 50 yards does the source characterize it as "very accurate"?
• You've described a few different crew positions; people watching each of two different scopes, and "the range readers", which I suppose are the same people. It would be useful to give an exact rundown of how many people were in the crew and what each person did.
  • Still needs to be addressed.
• could be attained with these lobe switching systems. a reader who is familiar with antenna design will understand what you mean by "lobe", but most readers won't, so a short explanation (and, again, a diagram) would be useful here.
• It was found that in certain orientations of the transmitter and receiver, the small antenna used to trigger the time base would see too small a signal to work I'm confused. I think what's going on here is that the time base sync is sent from the transmitter shack to the receiver shack by radio, but that's not clear. Again (and I know I'm getting repetitious here) a diagram would help.
• By late 1939 became clear "IT became clear"?
• well into an effort to build an S-band GL radar system I know that S-band means a certain wavelength (although I had to go look up the exact number), but most readers won't have a clue what you're talking about. It's especially confusing since if you click on S-band you get to an article that's talking about frequencies, and most of this article has been talking about wavelengths. They're just two different ways to say the same thing, but most readers won't understand that. So a short explanation here would be useful.
• it combined scanning and tracking into a single unit with an internal generator set that touches on something I've been wondering about; where did the Mk I and II units get their power? I assume in addition to the receiver and transmitter shacks, there was a separate generator shack that came along with it? How many total vehicles did it take to move and set up one of these units?

At this point, I'm done with Development. I'll pick up again with the rest another day.

Many edits, I think I got everything on your list. Some notes:

• half-wave is already there, just above.
• sawtooth is definitely the correct term.
• a-scope is linked already just above.
• it's not a yagi. Similar, but different. It's actually built exactly like a modern UHF TV antenna, with dipoles in front of a passive rectangular reflector.
• I just removed the s-band, simply say "microwave" seems good enough in this article.
• I do NOT have a description of how this was hauled. This is actually a bit curious because all the other units I've worked on always go out of their way to describe this, right down the individual model of trucks. Maury Markowitz (talk) 16:43, 19 December 2024 (UTC)

Description

• In some places you talk about "wooden cabins", in other places, "wooden huts". I assume these two terms refer to the same thing, so it might be clearer if you just stuck to one consistently, or at least at the first usage, say something like "cabins or huts".
• I'm also curious (and I assume so will our readers be) why these were built of wood. Was it just a convenient material or was the fact that wood is not electrically conductive an important factor?
• mounted on AA gun carriages Readers who know about these things will know what AA means, but many won't. So you should define the term. I'm assuming these were used because they included the ability to support a great deal of weight while being able to be pointed accurately in any direction in addition to being towable behind a truck; if that is indeed the case, saying so will be valuable to our casual readers.
• with up to 50 kW of power again, needs to be clarified that this is (I assume) peak power.
• the entire area in front of the transmitter antenna's current bearing given the subject matter, when I see "current", I think Electric current, so could you pick a different word here to prevent confusion?
• the signal was even less directional vertically than horizontally it should be mentioned (obviously with a RS, not just my say-so) that the narrower horizontal beam width was a direct consequence of the antenna being wider horizontally than it was tall, and that the antenna was intentionally shaped like that to achieve this effect.
• potentiometer which exponentially increased the charge in a capacitor bank This is confusing. Earlier you said The system worked by charging a capacitor at a known rate until it reached a threshold that triggered the time base which makes sense (and is basically the same as the variable trigger delay in modern lab oscilloscopes, at least until the end of the analog scope days), and by "known rate", I assume "linear". But here you're talking about charging at an exponential rate, which I don't understand.
• for reasons that are not recorded in the references, this solution was not used we're supposed to be using WP:RS, so I'm unclear where this bit of information came from.

OK, that does it for a first pass from me. Overall, this was an enjoyable read. As noted in a few places, I think the addition of some explanatory diagrams would go a long way towards helping a non-expert reader understand how this all works. I know a fair bit about radar, so I was able to fill in a lot of the gaps from my personal knowledge. I suspect most people will just be lost, however.

Some other random thoughts...

• The introduction of the cavity magnetron in 1940 led to a new design effort using highly directional parabolic antennas to allow both ranging and accurate bearing measurements while being much more compact is a little deceptive. It's not the parabolic antennas that allowed it to be more compact, it's the fact that it used shorter wavelengths. The greater accuracy may have been due to the parabolic antennas, but the shorter wavelengths is what allowed them build build those antennas in practical sizes. So I would certainly mention that the cavity magnetron allowed them to operate at those wavelengths.
• You should tell the reader what "gun laying" means

I think I have all of these as well.

As to the "exponential" bit, I have only this: "The design of the potentiometer is based on a time constant r = 167.1 microsec, the grading being exponential so that time-interval or range readings are linearly related to the angular settings of the potentiometer shaft." This is only used on the bearing display, the range display is different. Reading it now I'm not at all clear one what this accomplishes. Maury Markowitz (talk) 13:50, 20 December 2024 (UTC)

Most of your changes look good. I've noted a couple of items above which still need to be addressed. I know this may be going beyond the requirements of WP:FACR, but I'll repeat my suggestion that some good diagrams in a few places would go a long way towards making this approachable to a non-expert reader. I understand most of the technology here so I'm able to do a lot of imagining how things must be arranged and I'm really just filling in details as I read along. Most readers, not so much. I recognize that this is a highly technical subject so it's unreasonable to expect that somebody who knows nothing about electronics will be able to follow every detail, but I do think there's room to do better in this regard. RoySmith (talk) 02:48, 23 December 2024 (UTC)