fullsquare
joined 7 months ago
if you have an antenna with impedance of, say, 200 ohms, then you need to match it to transmitter impedance of 50 ohms, or else most of power output from transmitter would be bounced back and will damage output stage of amplifier. because on receive currents are tiny, you can wing it by just using it without any match and connecting it directly
transformers are not the only way to do this, and some other circuits can be used instead. if you take a transformer with 1:2 winding ratio, then if on one side current is 1 and voltage is 1, then on the other current will be 0.5 and voltage 2, which means that impedance increases 4x. in EFHW, it's 1:7 winding ratio and impedance ratio is 49x, which works for end-feeding a half-wave dipole, just as expected (from 50 ohm to ~2500 ohm). that transformer is a limitation on power usable in this antenna and main reason to use this type of antenna is mechanical
most importantly, transformers work nicely only if you have real impedances, so your antenna has to be resonant anyway. l- or pi-network tuner will also handle complex impedances so doublet or random wire will work nicely with it, as long as you can accept weight and losses in tuner
how compact and what do you want to do with it? if it's for receive only, the most compact you can get is ferrite rod antenna, but it's very different from usual wire antennas used for transmission. if using wire antennas, random wire would be fine
it depends on whether you want to transmit or not. if not, you can just use random wire antenna
random wire antenna is exactly what it says on the tin - length of random wire strung up as high as you can, as long as you can make it work. the other part is ground, where you might want to lay some lengths of wire and connect them in a single point, to act as radio ground. it won't have right impedance (probably 50 ohm) but for receive, this is ok - it'll be probably usable, and you can amplify signal without penalty because amplifier noise will be much smaller than atmospheric noise already present. the amount of power bouncing around is tiny and can't damage anything
if you want to transmit, you'll need more elaborate antenna. what you can use depends on whether do you have a tuner like neidu3 describes or not. if you do, common choice is doublet which is a specific length of wire connected to tuner with a 400-ohm parallel line. if you don't, common choice is halfwave dipole which is halfwave long, and put as high as you can get, either vertical or horizontal, but for practical reasons mostly horizontal, or monopole, that is quarterwave long, but requires lots of wire on ground to act as radio ground. you can make them shorter using coils, but this makes bandwidth narrower. in any case, it'll be need to be tuned to your band in question, for which you need a tool like nanoVNA. tuner also narrows your bandwidth, but you can retune it so it doesn't matter that much. (it'c called instantaneous bandwidth)
wait, i thought these turbines were already backordered because of them? not only regular gas turbines but also these converted ones. gas turbine is gas turbine
this is on top of power transformer shortage (which are always backordered, but were backordered before 2022, then ukrainians started buying more because their own got bombed, then techbros made backorders bigger)
238Pu is made from 237Np, which is almost pure isotope recovered in spent fuel reprocessing, especially for weapons use. americans stopped doing that in one of their major sites in 1988, ran out of it in 1993 and bought it from russia ever since, but russians also stopped making this isotope because it's mostly weapons grade plutonium byproduct and they have enough of it. americans still do some reprocessing but not enough to meet NASA needs, but also they started ramping it up to some degree. i understand that 241Am will be used to cover this gap at like 5x greater isotope weight
slight clarification here
so i looked it up again and this plutonium was already declared surplus, and was slated for disposal for 25 years now. it's a part of 34 tons of plutonium that both russia and us each were supposed to dispose of, as agreed in a treaty. that disposal consists of using plutonium as fuel, because irradiating it in reactor for a long time makes it useless for weapons use. russians did their part, in part because they were using plutonium in their own power reactors for a long time, so they could just use existing infrastructure. americans didn't, and they wanted to contaminate it with something and store underground, but some people wanted to burn it in reactors as it should be, so they instead did nothing and they still have some of that plutonium in there. that contamination can be probably reversed so russians objected to it, and didn't like that americans did nothing either. this is why russians suspended this treaty in 2016 and formally withdrew this monday. therefore it was a fire sale then and it is a fire sale today
and the reason for why americans don't have infrastructure or expertise to use plutonium as fuel is at least partially another fire sale, which used up russian ex-weapons uranium for fuel in american powerplants and started five years prior (russia was flat broke in 2000). rosatom became significant fraction of nuclear fuel supply worldwide (until that ex-weapons uranium ran out), that pushed nuclear fuel prices down and guided management decisions against plutonium-based fuel in infinite wisdom that uranium will stay cheap forever (plutonium remains more expensive now, but it doesn't have to be the case forever). another big one was american policy against reprocessing spent fuel. couple of other countries have national energy utilities that have different priorities and do recycle their fuel in way that would be useful for the program above, weren't part of this program and continued to use plutonium for multiple reasons. americans could ask for technical assistance from french or japanese or other allied countries, or perhaps even pawn plutonium to them, but i guess that not-invented-here syndrome won
i don't know what kind of diplomatic win are they trying to get there, if any, considering that russians don't care about this treaty anymore and had more surplus plutonium anyway
i wonder if someone pointed that thing at tarpit already
wint @dril 29 Dec 2014 and another thing: im not mad. please dont put in the newspaper that i got mad.
long hand of casey newton (by proxy) outputs a weird hit piece on ed zitron in wired https://archive.is/chsCw so far bluesky in shambles with no other effects