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Cake day: March 31st, 2025

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  • you can’t turn a gas into liquid by compression alone if temperature is above critical point, you also need to cool it down. separation is done by fractional distillation, but the reason it’s done is mostly about oxygen (medical and steelmaking among some other uses). for nitrogen it’s somewhere about -150C. first air is stripped of water and carbon dioxide, then it’s turned into a liquid, then it’s separated into oxygen, nitrogen and argon, and some large specialized plants also separate xenon, krypton and neon

    if you don’t actually care for it being a liquid, there’s another method called pressure swing adsorption that separates gases based on how tightly do they bind to porous surfaces under pressure. this is how medical oxygen concentrators work

    making liquid nitrogen is pretty efficient these days, as in not much more energy is used than is actually needed




  • this is just a really extravagant heater, physics forbids antenna this small to have good radiation resistance. for your contrived below noise communications scheme, you need more bandwidth that is physically possible on hf, yet you choose antenna design that is even less wideband than regular dipole. 40m of wire is for 80m band, which is usable more often in this configuration, ignoring everything else

    As for throughput: a channel that is 9 KHz wide is supposed to transfer 9.6 kbit / s

    5500kbps in extremely favourable conditions is your peak attainable speed, bandwiths in normal radios are narrower

    A reasonable detection avoidance technique might be broadcasting from a depressed location or an urban canyon with tall ground clutter

    if you don’t want anyone to hear you

    launch your guerilla transmitter on a free flight balloon, and will have plentiful line of sight.

    with what power source? better study for and get your license, start using radio and stop embarrassing yourself




  • yes i know how spread spectrum schemes work, but this is not really practical or relevant here

    for spread spectrum things to work you need some wide bandwidth, this works great for microwaves where you can spread your 90GHz band signal so that it covers 5GHz, you can’t have a signal centered on 5MHz that is 5GHz wide; HF is relevant because while microwaves work with this microwaves are line of sight only and most people’s line of sight still terminates in their own country. if you live on a lone hill next to border good for you, but the rest would need to use HF to get out, and there’s simply not that much bandwidth available in the first place, which would make any scheme like this extremely slow if at all viable. and you can still jam it

    i don’t assume that satellite repeaters would be a viable option because satellite, or any other receiving party for that matter, would need to be aware of modulation scheme to receive it in the first place, so it only works if your international contacts are pre-arranged, and even then you need radio that has much larger bandwidth that is usually available. yapping on LSB or narrow digimodes will get you heard within continental range, but also it will get you noticed, but if you hide from your adversary you also hide from everyone else not in the know. and even then, you can still get noticed, because it’s under noise level only at some distance from you

    also some of these schemes require precise time to be known, and if you have gps jammed you’ll get extra problems from that