23
submitted 1 month ago by [email protected] to c/[email protected]

I did a thing, and it even worked. Probably mechanically the simplest way to make antenna with gain over dipole is to use two 5/8 lambda elements, but really anything longer than 1/4 lambda already gives improvement, 5/8 is just maximum. No coils or other delaying elements within radiating part of antenna are needed, with disadvantage that impedance is complex. Normally, this is dealt with by putting coils at the base, but there are other options.

Some variants of single stub tuning appear in J-poles and beta/hairpin matches. In general, it only takes single transmission line and two variable positions of shorting bar and feedpoint, and it can match any impedance at single frequency, given appropriate choice of that transmission line impedance. I've picked 240 ohm - lowest I could get away with - and it wouldn't allow to match normal 5/4 lambda antenna, so I shortened it instead to 1.1 lambda - this gives higher initial impedance that is easier to match this way. (Sometimes I could find impedance of this antenna given as 150-850j, but this is just twice impedance of 5/8 lambda monopole, assumed to be thin. Analytical formula on wiki page gives for 5/4 lambda, 5mm wide dipole for 435MHz 214-330j, maximum usable transmission line impedance would be closer to 200 ohm then. Actual simulation like in NEC would be more trustworthy)

Construction wise, this is rather simple device. I've used two pieces of 5mm aluminum wire for dipole and matching section, and connecting blocks cut in half and soldered on the bottom side for connections to shorting bar and feedpoint. This allows for easy moving of both and relatively effortless matching

I'm pretty sure that balun like this is proper overkill, but I wanted to make sure that common mode currents don't mess my measurements. Tuning turns out to be pretty straightforward, with feedpoint position having bigger influence on SWR than shorting bar position. End result is rather wideband, with SWR just 1:1.2 on edges of 70 cm band:

Being 1.1 lambda long (80cm on 70cm band), this antenna is probably suitable for VHF-UHF only. On lower side, radiator length starts to be unwieldy (6.5m on 6m band, 2.3m on 2m band), on higher end, matching section would become tiny. The latter limitation can be probably solved with use of PCB traces forming both radiating element and matching section (board size approx 15x5cm should be sufficient for 13cm band - two sides and at least one via needed), which would also allow for lower impedances of transmission line, therefore getting closer to 5/4 lambda length. (This would probably require considerable number of simulations and prototyping, both beyond my abilities right now). On lower VHF, perhaps 70mm or similar drainage pipe could be better waterproof housing for matching section, especially if balun can be skipped and if matching section turns out to be long. Wires can be probably extended beyond shorting bar and used for support, like it is sometimes done with J-poles.

Any criticism, advice, good practices, tips, etc welcome

Some tools used https://hamwaves.com/zc.circular/en/index.html https://www.will-kelsey.com/smith_chart/

55
submitted 3 months ago by [email protected] to c/[email protected]

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

[-] [email protected] 113 points 5 months ago

careful, lw mods don't like that

130
submitted 5 months ago by [email protected] to c/[email protected]
279
submitted 5 months ago* (last edited 5 months ago) by [email protected] to c/[email protected]

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

[-] [email protected] 155 points 5 months ago

i mean military just showed up, did absolute minimum just so that they can't be prosecuted for refusing orders, and when parliament voted martial law away some of them left (before being ordered so) then the rest left anyway. they knew what was going on and didn't want part in this

500
submitted 5 months ago by [email protected] to c/[email protected]
[-] [email protected] 105 points 6 months ago

"preventing next corn plague" with resources used being a box of soil and bunch of underpaid grads seems pretty efficient to me, but i guess that since the common clay of the new west already voted they can be safely disposed of

at USDA, they're turning beetles kinky! 😡

  • alex jones fuming aimlessly while being stored in some container
263
NATO or nukes, remember? (discuss.tchncs.de)
submitted 6 months ago by [email protected] to c/[email protected]
[-] [email protected] 111 points 8 months ago* (last edited 8 months ago)

Nobody should trust LLMs with anything

ftfy

also any inputs are probably scrapped and used for training, and none of these people get GDPR

[-] [email protected] 188 points 8 months ago

Coming from a motherfucker who made up hyperloop vaporware specifically to fuck up cali high speed railways

78
go and apologize (discuss.tchncs.de)
submitted 9 months ago by [email protected] to c/[email protected]
199
mopup rule (discuss.tchncs.de)
submitted 10 months ago by [email protected] to c/[email protected]
220
4k ultrahd rule (discuss.tchncs.de)
submitted 10 months ago by [email protected] to c/[email protected]
119
suspicious rule (discuss.tchncs.de)
submitted 10 months ago by [email protected] to c/[email protected]
281
foraged rule (discuss.tchncs.de)
submitted 10 months ago by [email protected] to c/[email protected]
321
pain rule (discuss.tchncs.de)
submitted 10 months ago by [email protected] to c/[email protected]
[-] [email protected] 127 points 10 months ago

monkey jpg owners in shambles

[-] [email protected] 176 points 11 months ago* (last edited 11 months ago)

is that some american problem i'm too euro to understand? we got rid of this anticompetitive shit in early 10s

[-] [email protected] 131 points 1 year ago

also almost non-corrosive, non-toxic, doesn't damage ozone layer, zero global warming potential, non-flammable etc (lots of organic rankine cycle fluids fail one or more of these. tradeoff is utilization of lower temperature sources)

[-] [email protected] 119 points 1 year ago

you focus on that popup and ignore all the crank shit that is on this page

yes a piece of granite (?) with $60 pricetag put on my amplifier COMPLETELY changes how my vinyls sound like

statements dreamed of by the utterly deranged

[-] [email protected] 299 points 2 years ago

times have changed

[-] [email protected] 120 points 2 years ago

you underestimate people's complacency and inertia, in no way this is end of reddit

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skillissuer

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