who is “we”? as of now, there’s still oil being extracted and fertilizer being produced, just a bit less of it. if you live in a western country you don’t have to worry too much about it, except higher prices of food and everything that gets transported. if you’re a subsistence farmer in a place like bangladesh then you’re to some degree fucked

openhamprep explanation is wrong

When you consider a segment of wire, it has some inductance and capacitance in that small segment, and the wider it is, the lower inductance and higher capacitance are. In other words, both X_L and X_C go down as diameter increases. Electric field lines within antenna are mostly perpendicular to wire everywhere except on ends, where they spread in all directions, which means that there’s some residual capacitance there that needs to be charged each cycle. This is called end effect and the wider wire is, the more of it you get. In fact, the same aspect ratio (length/diameter) gets you the same end effect ratio each time, and it’s usually in range of 0.98-0.95. If there’s insulation, then insulation has lower velocity of propagation as it has higher permittivity than air, and it is in place with highest electric field intensity, and this can also shorten necessary wire length a couple %. The more insulation there is, the more shortened antenna becomes. have a calculator: https://www.translatorscafe.com/unit-converter/en-US/calculator/dipole-antenna/

But wait, there’s more. We can think of antenna as a lossy RLC resonator (sort of), where R is Rrad which for halfwave dipole would be 72 ohms, + loss resistance which is smaller, and neither are changing fast with frequency. What is changing faster is X_L and X_C, and the wider wire is, the smaller both of them are (X_L = -X_C at resonance), and this means that you can go further off frequency and still have acceptable SWR, i.e. antenna made with wider wire has more bandwidth, or if we look at it as resonator, lower Q. For HF this means using masts or wire cages instead of single wire, but for VHF this gets more practical

Resistive part of antenna impedance near resonance depends on physical antenna length, and if antenna is shortened, then how it was done, but for the range we’re here it won’t change much. But also it will depend on height above ground, type of soil, antenna geometry and many other things. 72 ohm is in freespace only

you can consider antenna wire as a transmission line, but it will need to include ground as the other side of transmission line, and then impedance is dependent on wire diameter to height over ground ratio. it’s not very useful except when considering very large and currently uncommon types of antennas (beverage antenna and rhombic antenna, both of which are traveling wave antennas)

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rtl-sdr uses the same chip as dvb-t tuners, but the everything else part is completely different

lol as if they could plan this far forward

cancer is in large part an old people disease, if you avoided dying of cholera you’re more likely to die of something else. also now there’s a lot of people who were exposed to carcinogens decades back, and we got better at treating pr preventing some other common causes of death like stroke or heart disease

that’s no problem at all, systems like that are in use

It’s easier to freeze water than to cool rock borehole

Saudis parked fuckload of money in ai startups

Lithium-iron is about 2x more expensive, there might be different availability and energy use during manufacture is probably higher

Lead-acid batteries work if you don’t care about weight and lithium-iron phosphate if you do

there are photos of 16 different radios and a couple of antennas, but the one in thumbnail is Elecraft KH-1

It’s up for you to decide. On U/VHF you can talk to other people directly (locally) like on HF. But you can also do things that HF can’t provide, or provides with limitations, like talk through repeater (uncommon on HF), or to ISS, or through satellites (HF bounces from ionosphere) or do longer distance communications from mountaintops, or do image transmission or packet radio (HF has less bandwidth). On receive only you can also download NOAA weather satellite images, or whatever else data are emitted by them. You can make your own repeater from two baofengs. HF gets affected by space weather, U/VHF is not, and we’re entering solar minimum. 6m will take you far further than 2m but it’s usually bundled with HF radios

On higher end there’s also moonbounce, but it’s not in the budget category

e: there’s 50 things you can do with SDR only (many on U/VHF) https://blinry.org/50-things-with-sdr/

Depends on what you want to do. UHF/VHF handheld radio can be had for 20-30, uSDX or QMX type small low power HF radio is closer to 100. You’ll also need battery, antennas (perhaps tuner) and something to put data in and out (headphones and microphone or cw key or audio interface to laptop) (no idea if it’s good but people use it)

this also happens with dc once voltage is high enough

It’s easier to see that this circuit is rather symmetric when you redraw it

Then with both switches closed blue wire (the one in the middle) should only carry small current. If both halves are exactly the same it should be zero

In general when circuit doesn’t include nonlinear components (semiconductors most commonly) you can sum two valid solutions and you’ll get another valid solution. Note that when one switch is closed, current in blue wire goes one way and when the other is closed, in opposite way

Could be. Amplifiers are a bit more complicated and there are many things that can limit bandwidth

If we consider groundplane antenna, which should be much better than anything that you can fit on a HT, it might be centered on 145MHz (region 2 band) and it’ll be good for 10MHz for 1:1.5 SWR (140-150) and 17MHz for 1:2 SWR (136.5-153.5) according to some random measurement, first that i found. Outside of these ranges SWR rises rapidly and if you tried to transmit on say 170MHz you might get SWR 1:5, perhaps 1:10 or worse if you’re unlucky. On receive this doesn’t matter too much because these nano- to microwatts of rx power would just bounce back harmlessly with the only effect being that apparent signal strength is lower. But if you tried to transmit then design currents or voltages would be exceeded and something will break, usually final stage of amplifier. This gets rarer than it used to be because some radios can measure SWR and will reduce power in such scenario. This also gets worse the higher transmitted power is

This happens because unlike on HF + 6m, on 2m and up ATUs are not a thing* and all antennas are expected to be matched. So you can use the same radio on GMRS or PMR or what have you and on 2m or 70cm band, but you have to change antennas between these uses. If you want to use all of these on one antenna, then there are special wideband designs like LPDA but this makes sense on a mast and not on handheld radio

* there are tuner designs that work on 2m and up, but you won’t find them in HT, there’s no point, they’re too big, too heavy and too expensive

Even if you tried and made it to work, there might be other incredible problems with things like harmonics or other spurious emissions because filters were not designed to work way out of these frequencies. For example you can try to force Quansheng UV-5K (?) to transmit on 60-ish MHz but most of the power goes out at 2nd and 3rd harmonic, because of the way filters were set up. Narrowband designs are much easier and this is what you’ll see all the time in amateur radio. Wideband and ultrawideband designs are constant source of job security for RF/microwave engineers

You can think of matching units and antennas (and to some degree even feedlines) as filters to some degree, because their bandwidth is not infinite

Note that there’s 25% of fractional bandwidth in there and many antennas won’t work everywhere in that range (and also other elements like power dividers, diplexers etc if part of circuit)

related phenomenon. at calm solar surface, there’s only hydrogen and helium. these are excited thermally and can emit radiation, but the highest energy photon they can emit is ca 13eV and 52eV respectively. this is vacuum UV, and this is what is responsible for ionisation of ionosphere even during solar minimum, mostly F layer. but when solar flare forms, there are these giant loops of charged particles, and when charged particles change direction or brake, they release a lot of high energy radiation, that is xrays. xrays just go everywhere and this is partially what is responsible for extra ionisation of ionosphere during solar maximum, and this contributes more to E layer ionisation. (because xrays can go further through air) when solar flare hits the earth, protons from it cause extra ionisation in D layer and this is why post-flare blackouts happen

this is also why one metric of solar activity is solar xray flux