skillissuer

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Check first on a smith chart whether transmission line that you can easily make or get and adjust its length has proper impedance for both source and antenna. The shorter length matching section has, the wider bandwidth you'll get. There are typically two solutions, of which one is better. Ideally you'd like to have transmission line impedance a bit lower than what would be needed if only transmission line part was used (without stub)

If you want to make a yagi, or mount antenna close to a mast and don't care particularly hard about extremely uniform coverage, you can modify impedance by changing distance to reflector. If you want to use something like this https://www.wa5vjb.com/yagi-pdf/cheapyagi.pdf then this antenna (radiating element) is already unbalanced and doesn't need balun that badly

I don't know if you need common current mode choke like this, it's probably overkill, popping 3-4 ferrite beads on normal sized coax should be enough. Some people don't even use it at all and things still work for them. You can also always use folded balun or sleeve balun as a common mode current choke. This toroid is only 20mm in diameter or so, and RG174 has minimum bending radius 6mm, so it's abused a bit but not that much. It's probably good for lower bands like 6m too. Alternative is to use a pair of twisted wire in parallel (these have 100 ohm impedance or so, two in parallel are closer to 50) wound on ferrite (more common on HF), and if size restrictions exist, you can use tall and narrow non-split ferrite bead instead of wide and short toroid like this one i've used. Also i made it this way because that's what i had in my drawer. Maybe it was not balun that was narrowband, but radiating element is a limitation instead?

[–] skillissuer@discuss.tchncs.de 2 points 3 weeks ago (3 children)

that's RG174, there's only 25cm of it or so, so loss is probably not a huge concern (53dB/100m at 400MHz, so 0.13dB), and that common mode choke is probably a bit too much anyway

[–] skillissuer@discuss.tchncs.de 2 points 3 weeks ago* (last edited 3 weeks ago)

not much? i don't have scale but 150g perhaps? i think that if you don't need it waterproof then you can just extend wires, use them for support and get rid of case entirely. this would require sturdier shorting bar and some spacers probably but would be more compact

it's 80cm long and can't be folded, so if that's portable enough for you, then yes

the point of this antenna is that it has something about 2-3dB gain over dipole, if you don't need this a lots of smaller antennas with dipole gain exist

e: and also despite what its size could suggest it's a single band antenna, this one is for 70cm but if you have space for 2m (2.3m long) then i think it still should be practical

 

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/

[–] skillissuer@discuss.tchncs.de 8 points 1 month ago* (last edited 1 month ago)

mercenaries would be something like wagner. there are international volunteers within normal units of UAF, with normal pay and responsibilities just like any other unit. these chinese were promised unusually high salary and russian citizenship at the end of the contract. ukrainian foreign legion is entirely official, while this chinese recruitment seems to be covert or at least not very highly visibly public. ukrainian foreign legion also takes only people with former combat experience (iirc), it's unclear so far if chinese recruited have any, probably not considering that china has stayed out of any major war or deployment since forever. these are not the same things

additional layer is that according to comments first track is also used in chinese nature documentaries

[–] skillissuer@discuss.tchncs.de 15 points 1 month ago (1 children)

in some cases, on the power of the "fuck that other other guy" school of geopolitics, this can be avoided. https://en.wikipedia.org/wiki/2024_Iran%E2%80%93Pakistan_border_skirmishes "you see, we actually targeted separatists" "yeah we also targeted separatists let's call it even" it also requires certain degree of diplomatic finesse that trump lacks, and there's no good reason for strikes in the first place considering that dea coordinated with mexican police (?) previously, so they could just continue doing that

[–] skillissuer@discuss.tchncs.de 7 points 1 month ago (3 children)

of course MBA came up with this

an airplane doesn't flap its wings

behold this fever dream animation

now you've got me thinking if storage in fridge is necessary at all, if these are salts. worst thing that can reasonably happen is that salt picks up some water from the air, on top of water condensing on sample when vial was opened while still cold. freebase would probably be air-sensitive, but for compounds that are known sensitive i'd put them under argon/nitrogen, tape vial shut (with normal electrical tape, not parafilm) and store in freezer instead. sigma lists storage temperature for MDMA analytical standard (weak solution of freebase in methanol) as -20C, but some of this might be legal cover with excess requirements for cases where you'd have to be absolutely sure that analytical standard didn't decompose (like in evidence in drug cases)

[–] skillissuer@discuss.tchncs.de 14 points 1 month ago

there was a reddit ama with an ukrainian dude who was in charge of procurement of certain drones for ukrainian army. among these were uavs from anduril, and uaf decided not to buy them, chiefly because these drones don't work and cost something like 20-50x more than equivalent ukrainian designs that do work. the reason why they don't work is russian jamming, about which anduril people presumably were informed, yet somehow they still were complete assholes (to foreigners only) through entire process. which also means that ukrainian elint captured how russian jamming works, gave that data to anduril who proceeded to do fuck all with it, possibly leaking this intel in some signal chat

the reason why these were on the table to begin with is that (part of) american weapons aid is provided in form of money to be spent at american manufacturers, it's not pallets of cash like fox news would like you to believe. (private donations to places like united24 do work this way, but also for example denmark does provide money with no strings attached, at least not these). (yea i'm effectiving my weaponized altruism, cranking up these numbers of dead russians per thousand euros). reasons for that are slight wage discrepancy between poltava and berkeley, compounded by scale (how many drones does anduril make per year, 20? ukrainians make low millions, probably with thousands to hundreds of thousands per type). most of costs in drone development is driven by software. doesn't help that thiel's people are swamped in vc money, therefore they don't have to work efficiently, neither have their drones, or even they don't need to work at all. ukrainians don't have the luxury to blow millions into ai swarming that doesn't work and instead put that effort into signal processing to avoid jamming, which does work, which they can check pretty quickly too.

this is the disruption they're cooking. invest in eastern europe or something

 

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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