skillissuer

joined 2 years ago
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these posers would repost "i fucking love science" on facebook but clearly never came back home in dead of the night after 13-hour shift in lab smelling of cum and mothballs because of a minor accident that nevertheless allowed to push envelope of known world just that little bit farther

antenna making is art of tradeoffs. there are different ones between size, cost, weight, mechanical and electrical complexity, wideband performance, radiation pattern, efficiency, and use of harmonics if any.

for VHF and up, it only makes sense to make single band antennas because cost and size savings are tiny otherwise, but bandwidths are large and there are no reasonable autotuners. there are special cases such as 2m/70cm antennas that can do both, but that's it. this is area of simple or folded dipoles, halos, yagis, LPDAs, helical antennas, and in bigger end of scale antenna arrays and optical-like systems like parabolic reflectors

for HF, if you have budget and real estate for it, some of best antennas money can buy would be LPDA for entire range you're interested in. this thing, however, for 3-30MHz range would be a giant aluminum triangle 40m wide, 50m long, weights well over a ton and needs mast and rotator because it's directional, not to mention that it costs fortune. but on balance it can reject noise from wrong directions and is always matched

some typical approaches are as follows:

  1. single band wire antennas. these would be halfwave dipoles in any shape (straight, inverted-v, slopers, off-center and so on), j-poles, groundplane antennas, quarterwave dipoles (requires good ground) and couple other variations. these are light, cheap, efficient, fit entire single band without gross abuse of finals, have uniform radiation pattern. but only on one band, and having multiple of them in proximity can lead to weird effects, so these are best if you're hiking for example, but good in general

  2. principally single band wire antennas but now we also want to squeeze some other bands out of it. these are dipoles - normal or OCFDs, full wave loops in one approach and trapped dipoles in other. in first case, we exploit the fact that there are usable harmonics on some bands - 80m has 40m, 30m, 20m, 17m, 15m, 12m and 10m. 40m has 20m, 15m and 10m. 20m has 10m. but depending on type not all are always usable and higher harmonics will have narrowed usable band compared to single band case. in trapped dipole approach there's a limit on how many traps you can put (mitigated to some degree if you make it asymmetric and put traps on one side only), and as traps work as coils, these shorten antenna which also narrows usable bandwidth but now for lower bands, opposite of the former. use of autotuner and low loss transmission line can make it work over wider bandwidth, but this only goes so far. note that some bands are narrower than others (12m, 17m, 30m, 60m) and it can be made to work for these pretty well, but less so for others (80m, 40m, 20m, 15m, 10m), but it can still work if there's less bands on one antenna, especially if you're not interested in entire band (like for CW-only or voice-only operators), are willing to accept some loss of power, or use tuner, or combination of some of these

  3. antennas that are by themselves not resonant at all. these are either lossy (like terminated dipole) or require tuner, sometimes purpose-built and can be narrowband when tuned (doublets, magloops) both can be reasonably compact. because match lies in tuner, these are multiband by virtue of changing tuner settings. terminated antennas have good match but also you can be dumping half of power or more in resistor. there are also ways to use mast antennas in this way, even if they are grounded (using gamma-match for example)

  4. antennas that have to be extensively electrically shortened because wavelength is huge. these are generally everything from 160m down. these are things like magloops and bespoke wire antennas with loading coils and capacitive hats and such. because these are short in comparison to wavelength, efficiency is small and bandwidth is tiny (but can fill entire band) but also require extensive space just due to how huge wavelength is

  5. some directivity can be achieved by making yagis (higher part of HF) or by deploying multiple antennas in an array. depending on band and type of antennas this can get very elaborate and expensive. simplest and cheapest way uses multiple radiating halfwave elements connected by coils, or with parallel parasitic elements. this can get decently directional while also being a bit compact but also this makes it more narrowband and due to large size only makes sense for higher HF and VHF

but start simple. single band wire dipole or j-pole would be probably best in your situation

[–] skillissuer@discuss.tchncs.de 1 points 5 hours ago (1 children)

what impact would it have on division of seats for other parties?

[–] skillissuer@discuss.tchncs.de 3 points 6 hours ago (3 children)

is there a possibility that FDP falls under electoral threshold this time?

[–] skillissuer@discuss.tchncs.de 48 points 21 hours ago (3 children)

People who boast about their IQ are losers ~Stephen Hawking

[–] skillissuer@discuss.tchncs.de 3 points 21 hours ago* (last edited 21 hours ago)

you might have problems with your EFHW balun being too lossy/undersized. check if ferrite heats up when transmitting

[–] skillissuer@discuss.tchncs.de 2 points 22 hours ago* (last edited 21 hours ago) (1 children)

you're looking for 2 or 3, possibly more, separate antennas. consider: a groundplane, sleeve dipole, copper cactus, halo antenna or small yagi (2-3 el) for 2m; you might get away with operating them on temporary stand, or even from inside apartment. groundplane for 10m (can be made from wire; 10m is wide and you want separate, single band dipole for this reason); and some kind of wire antenna for 20m, maybe also for 10m. depending on conditions one or another might be better (vertical vs horizontal polarization, height above ground etc).

one way to make the latter is OCFD, this way you can make antenna for both 10m and 20m; for this one you'd need some matching scheme based on specific feedpoint position, specific coax lengths (5m is halfwave at 10m so won't change impedance at this band, but can be used to match 20m) or 1:4 or some other balun. see there for more info you can also try a full-wave loop for 20m if you have enough space, it'll work for 10m as well. same applies for matching, that is, if you don't have autotuner (but where's fun in that?). you can even make single band j-poles from ladder line/window line and wire even for 20m band, and string them from your window all the way to tree on the far end. you might want to put a pulley on a tree for that, and all antennas can this way be rolled and fit in your backpack, or maybe even pocket

these commercial antennas are expensive, you can have another radio for this kind of money

[–] skillissuer@discuss.tchncs.de 6 points 1 day ago (2 children)

study or preprint?

[–] skillissuer@discuss.tchncs.de 5 points 1 day ago (1 children)

at least glass is nontoxic

 

so i stumbled upon a thing on reddit

the thing is that there's an obscure early scifi book by none other than wernher von braun, that is about mars colonization, where they find already existing civilization, leader of which is called elon. apparently this is why megaracist elon's father named him that:

Interest in this novel increased in 2021 when people connected the Martian leader, called the Elon, to SpaceX founder Elon Musk, suggesting that von Braun may have somehow foreseen Musk's space exploration ventures.[15] However, Errol Musk, Elon's father, asserted in 2022 that he was fully aware of the von Braun connection in naming his son.[16]

also in that book: tunnels used for high-speed travel; nation-states became obsolete because of some magic tech; highly technocratic planetary government as a result. that stimulant habit seems historically accurate then, even if it's cut with ketamine sometimes. some more red string on corkboard https://www.mind-war.com/p/the-elon-how-a-nazi-rocket-scientist this tracks as one of his grandparents moved from canada to south africa because canada in 40s wasn't racist enough for them, and with all the technocracy inc things.

so yeah, motherfucker might be believing - or even groomed into - that he's destined to be a planetary overlord, all based on nazi scifi, and he's playing it out irl with all the fuck you money he has

 
 

Flight path of a plane that took off from Damascus shorty after news broke that Assad left the city towards unknown destination, which might have been Latakia on Syrian coast which is still under SAA control as of now. Terrain in place where flightradar stopped tracking that plane isn't especially suited for emergency landing

Shortly after crash Syrian Army Command informs officers about fall of the regime https://xcancel.com/Alhadath_Brk/status/1865587913817305454#m

update: it's not spoofed transponder data or controlled landing, locals reported plane crash in the area. rumors so far, but dawn will break soon in Syria and we'll know https://xcancel.com/Schizointel/status/1865593800678130081#m

clarification: there's some chance that Assad went out of Damascus before on other, private jet, so it's not sure and it's all conjecture on unproven information

update 2: there's a claim by Russian media that Assad is in Moscow, so he would have to flee on some earlier plane, but no photos as of now. Still, looked mildly credible at the time

 
 
 
 
 
 
 
 
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