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fullsquare

@ fullsquare @awful.systems

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716
Joined
12 mo. ago

  • 3D printed motorized variable capacitor, butterfly-trombone hybrid (also question on dielectric losses in capacitors)

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  • i was thinking more like, thin external plastic shell and empty cells inside, perhaps with another thin plastic shell on inside, and internal metal shell (on plastic support?) fitting in snugly, for mechanical stability, idk 3dprinting

    keeping leads short and nonmagnetic (dramatic reduction in skin layer depth) would be a good thing because of losses, but the longest object in capacitor would be just capacitor plates, and either way in wavelength terms it's rather small. more precisely you can model it as open transmission line stub with some weird and low impedance, but it's so small that you don't have to. you can also make capacitor shorter and wider, or even add more layers like how vacuum variables are made. in nesting design you can get taper effect just by making inner layers longer

  • Testing a shortened OCFD

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  • 3D printed motorized variable capacitor, butterfly-trombone hybrid (also question on dielectric losses in capacitors)

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  • The dielectric between the plates in this case is 0.4mm of ABS plastics (+ a bit of air in the 3d print layer lines).

    in terms of losses, PP or PE is a bit better than ABS, teflon or FEP is a bit better than PP, but air is superior to either (this is part of the reason why foam coax is a thing). not sure which ones are printable, or whether it's practical at this size, but try to introduce as many voids as possible (perhaps requires larger thickness of dielectric). it doesn't matter much in your case, because of low power (warping of plastic because of excessive heat is probably not a problem). if your coax has solid dielectric, then by introducing enough air in 3d-print your variable might become less lossy than that

    The Capacitors allows my 80cm diameter loop to tune from 20Mhz to 37Mhz. Sweeping the whole range is a bit slow due to the low RPM of the motor and takes about 6min. But that is kinda nice when fine adjusting to a frequency.

    you have probably noticed that position vs resonant frequency relationship is rather nonlinear. you can get higher sweep speeds at lower end without losing much accuracy at higher end by tapering end of side plates into a triangle shape (it will get longer overall). it doesn't matter much in your case, because it's all approx monoband, but if you want to go multiband with this, then it'll be a nice enhancement. similar effect happens when air variable capacitors have moving plates shaped in such a way that one end is longer than the other, and external edge has shape roughly like a section of logarithmic spiral. precise movement of variables like this is done by use of worm drive with large wheel

    I am not sure what is causing this, but i assume it could be due to increase of dielectric losses in the capacitor getting bigger when more of the plates overlap because then the electric field has to flow thru a bigger area of dielectric, increasing the potential for losses.

    loss tangent of dielectric is material property, that is ratio of equivalent loss resistance to capacitance should remain constant at given frequency. so i guess that losses should remain roughly the same, if dielectric is to blame, but at any rate lossy capacitor should make bandwidth broader and SWR lower. my guess would be that it's a matter of coupling loop becoming wrong-sized or wrong-positioned at some point with change in frequency (try moving it up or down? there's gotta be some optimum position for your entire range of interest)

  • -1488 palantir social credit score

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  • The AI Scare Trade — the all-purpose excuse for number go down

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  • Stubsack: weekly thread for sneers not worth an entire post, week ending 22nd February 2026

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  • it's crazy how people memoryholed that (and japan doing the same, and a handful of other countries). or how until 2022 war norway wasn't really thought of as petrostate by people who didn't pay attention. or how ten years ago, if you said that putin bombed apartments to wage war on chechenya to win elections all to pardon yeltsin, people would think that you're a crackpot

  • Stubsack: weekly thread for sneers not worth an entire post, week ending 22nd February 2026

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  • no there's also racist twitter

  • Google criticizes Europe's plan to adopt free software

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  • Stubsack: weekly thread for sneers not worth an entire post, week ending 22nd February 2026

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  • i've collided with an article* https://harshanu.space/en/tech/ccc-vs-gcc/

    you might be wondering why it doesn't highlight that it fails to compile linux kernel, or why it states that using pieces of gcc where vibecc fails is "fair", or why it neglects to say that failing linker means it's not useful in any way, or why just relying on "no errors" isn't enough when it's already known that vibecc will happily eat invalid c. it's explained by:

    Disclaimer

    Part of this work was assisted by AI. The Python scripts used to generate benchmark results and graphs were written with AI assistance. The benchmark design, test execution, analysis and writing were done by a human with AI helping where needed.

    even with all this slant, by their own vibecoded benchmark, vibecc is still complete dogshit with sqlite compiled with it being slower up to 150000x times in some cases

  • Stubsack: weekly thread for sneers not worth an entire post, week ending 22nd February 2026

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  • yawn, i diagnose that LWer with weeb. this is something happening across entire industrialized world, causes being high performance mechanization of agriculture, old people being stubborn in regards to moving, lack of specialized work in countryside and couple of other factors. germany has patched their hospice staff shortage (not sure how effectively) with migrants, but japanese are way too racist for that. same thing happens in moldova, but you never hear sob stories about retired moldovans because they're broke and nobody cares, while moldovan govt can't really do much about it (because broke) to degree that it has not just economic and demographic, but even strategic effects. whole lotta drs strangelove in there

  • "When even A.I. hates A.I. Bros"

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  • more like coopting dissent for profit, libertarian selling tshirts with guevara type of thing

  • Exclusive: US military preparing for potentially weeks-long Iran operations

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  • and i told you before that it's officers (pilots are generally officers) that will be doing aerial bombing, and because large force on ground is prerequisite for situations you're describing, it's not going to happen

  • Clawdbot farm owner shares his bots have a 0.5% ban rate so far on reddit

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  • What's that discolouration on the silver spoon?

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  • this multicolored pattern looks like this because thickness of layer of whatever is comparable to light wavelength, mechanism is the same as in oil layers on water being colorful. it didn't spread from magnet, the layer is thinnest near magnet and becomes thicker near edges, which suggest it might be just dirt/oils that accumulated on it by contact. try wiping it with alcohol or acetone or what have you

  • Clawdbot farm owner shares his bots have a 0.5% ban rate so far on reddit

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  • according to his own claim, and he's selling his super secret methods. he might be just making shit up

  • Exclusive: US military preparing for potentially weeks-long Iran operations

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  • i mean that saudis were somewhat restrained about airstrikes, at least publicly, but this action would cause them to not be so. even if they tried, there are extra air defences dragged to saudi for exactly this purpose; every cargo flight and every extra warship makes odds worse for iran, as more missiles would be intercepted, but even if nobody dies, shooting missiles would have diplomatic consequences. another action that would result in rising oil prices would be iran shooting ships in strait of hormuz, but this would also close access to their own single large oil terminal, and there are american warships nearby anyway, so it's perhaps unwise decision to make today

    at this point, i think that decision to strike already has been made, and they're just stalling so that more metal can come from across the atlantic. dragging an aircraft carrier out there is not done for no reason, and the second one they want to put out there would need to have some of pre-deployment training shortened and done on the way, which is unusual and avoided because there were accidents that this training was supposed to mitigate

  • Stubsack: weekly thread for sneers not worth an entire post, week ending 15th February 2026

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  • should have glued it in place smh

  • Exclusive: US military preparing for potentially weeks-long Iran operations

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  • we'll see in a month tops

  • Exclusive: US military preparing for potentially weeks-long Iran operations

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  • i don't think it would go the way you think it would go

  • Exclusive: US military preparing for potentially weeks-long Iran operations

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  • right, let's see... they propped up unpopular (some 70% iranians oppose islamic republic rule, source), authoritarian, religious minority rule (only 32% iranians reported to be shia in 2020 survey, so before 2022 protests, it might be even less today), that was in a constant state of crisis and when president nho dinh diem got couped and killed, people danced on the streets (iranians burned down mosques and statue of soleimani during january protests). yeah, maybe iran is like vietnam after all, to be more specific like south vietnam during buddhist crisis

    i don't think that regular iranian population, that protested every year in almost decade and these protests were all met with crackdowns, mostly deadly, would like to see islamic republic rule to continue. neither i have heard anything about ground invasion, so all you've got out there is couple of pilots (officers) in the air and some more on ships