fullsquare
@fullsquare@awful.systems
- Comment on New clean energy comes out. *look inside* It’s just boiling water again… 45 minutes ago:
it replaces gas turbine with a fuel cell, which is a good couple % more efficient than CCGT. still under development. there is also another variant where hot offgas is generated under pressure and expanded directly. no steam, same effect
- Comment on The official HAM frequency designation is between 144mhz and 148mhz. So why are transceivers, even the monobanders, able to work on a much wider range? 48 minutes ago:
Could be. Amplifiers are a bit more complicated and there are many things that can limit bandwidth
- Comment on New clean energy comes out. *look inside* It’s just boiling water again… 1 hour ago:
there is a power generation scheme that uses high temperature fuel cells. optimally it could run on hydrogen only, but because it runs hot, it is able to take almost any flammable gas, along with some steam, and it forms hydrogen internally, then oxidizes it. this alone generates bulk of electricity, but offgas is hot, so it goes to heat exchanger which boils water, which then turns steam turbine
- Comment on The official HAM frequency designation is between 144mhz and 148mhz. So why are transceivers, even the monobanders, able to work on a much wider range? 6 hours ago:
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
- Comment on The official HAM frequency designation is between 144mhz and 148mhz. So why are transceivers, even the monobanders, able to work on a much wider range? 8 hours ago:
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)
- Comment on [FoAR] Foundations of Amateur Radio - CME, Wind, Flares, Flux and Geomagnetic Storms .. say what? #podcast 3 days ago:
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 hard 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. when solar flare hits the earth, protons from it cause extra ionisation in D layer and this is why post-flare blackouts happen
- Comment on [FoAR] Foundations of Amateur Radio - CME, Wind, Flares, Flux and Geomagnetic Storms .. say what? #podcast 3 days ago:
there are also solar xrays, which also ionize ionosphere and are associated with CMEs (regular processes on surface of sun cannot make much xrays, it’s only when high energy particles are smashed back at the surface xrays are emitted. intense magnetic fields are needed for that)
- Comment on How to tune my ladder-line J-pole? 1 week ago:
Huh weird. There must be something evil in that pole, it might be a piece of metal or maybe it’s wet or rotting inside. I’d use plastic things to tie it, because natural fibers will remain wet some time after rain, that might degrade performance. (zipties or nylon fishing line or whatever preferably monofilament). I see that bottom is secured too, this is good because in wind antenna could flap around and would stop working if it’s too close to the pole. If twin lead is slightly twisted and under strain (half turn per 30cm or so) then it should flutter less in wind, but you’ve got it spliced and i’m not sure how that would work. This is likely fine as is
J-pole type antennas are effectively monoband. They might work on 3rd harmonic which would be here 70cm band, but most of signal in this case goes up and down that is it’s useless and the signal that goes out horizontally is 6db weaker than what it would be with J-pole for that band. So you can take more precise measurement by zooming in to 130-160MHz or even 140-150MHz, this way you’ll see how low does SWR go at band edges because now you can only see that there is minimum somewhere in the band. I don’t know how much your radio tolerates, but 1:1.5 is generally pretty good. On receive only it might be good also at other frequencies, but dedicated antenna would be likely better
I don’t know if you have calibrated your VNA with cable or not, you can use Smith chart if you do calibrate it with cable but without it, SWR shouldn’t change too hard with any reasonable length of cable (Smith chart rotates once per half wavelength of feedline). This is useful especially if you make your own antennas, but here it’s fine just to make sure that SWR is low
- Comment on Why are plug sockets region locked? 1 week ago:
50mm^2 for 125A, just under 8mm diameter solid copper rod if it was solid copper rod. but it’s stranded so it’s a bit bulkier than that, bundled five per cable so also squished into a wedge. it adds up to some 4cm in diameter
- Comment on Why are plug sockets region locked? 1 week ago:
split phase is 2-phase system but everyone else uses 3-phase distribution. in reality americans also use 3-phase distribution, this is where 207v 3-phase comes from (it’s 120v phase to neutral)
- Comment on Why are plug sockets region locked? 1 week ago:
the entire point of three phase circuit is that you can split it into single phase circuits without using too much wire. usually block will be wired so that 1/3 of flats is connected to one phase, but if you need to power big loads like ag tools or something like concrete mixer three phase supply can be done (415V these days, there’s upward shift in voltage)
- Comment on Why are plug sockets region locked? 1 week ago:
in EU there are really only two standards. for single phase loads up to 3.8kW, regular 16A plug is sufficient. above that, 3-phase 5-pin 32A plug (most common of them) is used which can deliver up to 23kW. there are common variants of 3-phase 5-pin plugs rated up to 125A that can deliver up to 89kW, and uncommon up to 800A variants that are also part of the standard, but it delivers up to 0.57MW and it’s a bit silly
- Comment on Why are plug sockets region locked? 1 week ago:
modern smpss can take anywhere from 100 to 250V input so you can use them with either and any voltage inbetween. older ones had a switch between 240v and 120v modes (rectifier vs voltage doubler)
- Comment on Why are plug sockets region locked? 1 week ago:
blame edison for that
- Comment on How to tune my ladder-line J-pole? 1 week ago:
have you calibrated your nanovna? you have to do that after every change of frequency range
- Comment on Not a single one 2 weeks ago:
the man who decided to end german nuclear power production getting a seat in gazprom doesn’t inspire confidence in reality-based discussion of this subject
- Comment on Not a single one 2 weeks ago:
they also last decades and are cheap to run with extremely low carbon emissions
- Comment on Not a single one 2 weeks ago:
most of costs are costs of construction. french and koreans don’t seem discouraged and some plants in japan and china were built under budget
- Comment on [deleted] 2 weeks ago:
oops all Brassica
- Comment on What is a good delta between indoor and outdoor temps using only ventilation? 2 weeks ago:
I’m guessing the walls are retaining some heat.
Guesstimate your own numbers, but the way my flat is built walls have heat capacity some 150x more than air inside. (reinforced concrete building, walls/floor/ceiling counted as half if shared with other flats) You will need to run a lot of air through, at at least couple C temperature difference, to make a dent in that
- Comment on [FoAR] Foundations of Amateur Radio - The things you hear when you least expect it. #podcast 2 weeks ago:
That’s just the legal limit, i think we’re looking more at microwatt range or lower. Somebody on stackexchange measured power output of phone nfc module, and - measuring power received at secondary of air-core transformer - got 0.8mW. Assuming it’s representative, if all that power was fed into phone-sized magloop (10 cm square made out of 6 mm copper pipe) then at this frequency (13.65 MHz) we’re getting some -30dB efficiency so 800 nW. This is already very charitable overestimate, because NFC antenna is smaller, thinner, printed and multi-turn, and does not behave like magloop at all. Any response from passive device would be much weaker still. All of that uses high data rate (wiki says that ISO/IEC 14443 says 106 kbps), and because these things are where people live, there will be also a lot of urban noise. I’m not saying it’s impossible, but it wouldn’t be that easy
- Comment on [FoAR] Foundations of Amateur Radio - The things you hear when you least expect it. #podcast 2 weeks ago:
HF ISM bands as used (NFC things etc) are probably in sub-mW power range, there are regulatory limits on field strength and 27 MHz is additionally limited to 10 mW EIRP. Unless you have curtain that can hear signals from the future i don’t think there’s a lot to listen
- Comment on Made some J-poles 2 weeks ago:
No, width is your design parameter. I’ve only used 4mm wire because store ran out of 5mm wire. Were it all in air with no plastic, width is such that impedances of matching section are close to 300 ohm. Either way 4 or 5mm is not thin on 70cm so impedance of dipole will be probably lower than 5000 ohm, and entire band is covered so it just works
Pick any material you’re comfortable with. Start with 1 wavelength + couple cm of wire, measure out 1/4 and bend it so that 1/4 length point end up at the bottom most point. Tune by trimming (both arms, lengths of shorter and longer should stay 3:1) and match by moving feedpoint lower or higher (lower is lower impedance). That’s why I’ve made them this way, you can see marks from screw near feedpoint because feedpoint was moved a bit both sides during tuning. By the time trimming gets minimum SWR close to say 420MHz adjust feedpoint to get minimum SWR then alternate between trimming and adjusting feedpoint if necessary. Every mm counts, small trims are better done by filing the wire down instead of cutting it. Plastic needs to stay on during measurement. Keep some 1m of free space (without large metal things) around antenna during measurement
- Comment on Made some J-poles 2 weeks ago:
Paging @tasankovasara@sopuli.xyz for logistically efficient antennas
- Comment on Soldering 20m and 40m low pass filters from QRP Labs for RPi WSPR 2 weeks ago:
Most of the magnetic flux should be contained in ferrite, and the part that leaks is pointed at the middle of other ferrite so it shouldn’t induce anything. This is fine
- Submitted 2 weeks ago to amateur_radio@lemmy.radio | 3 comments
- Comment on Making a 1:1 Balun for Amateur Radio 3 weeks ago:
exactly, the ferrite only affects common mode current. you can think of coax as being composed of 3 conductors, core, interior of shield and exterior of shield. above some frequency and below frequency where coax starts to work like a waveguide, internal surface and core carry opposite currents (differential mode), and external surface carries common mode current. these can be treated as separate, except at the ends, because of skin effect. but also you can use twisted pair, because differential mode currents cancel out there
- Comment on What the caw? 3 weeks ago:
- Comment on My try for an apocalypse radio 3 weeks ago:
that’s just a piece of wire, perhaps some thin steel rope in a heatshrink attached to center conductor and trimmed to length. 1/4 wave at 2m which is fine, 3/4 wave at 70cm which means it’ll radiate most of energy upwards (wasted) when put on a conductive plane. this works because the other half of antenna is low power, handheld radio and operator (coupled by hand capacitively). putting 100W into it would be a bad idea because all that current will travel along the coax down to radio and operator except this time there’s an option of rf burns. for this kind of money, i’ve made two jpoles with extension cables, and the most expensive part was enclosure
i’ll make a post over the weekend about j-pole antennas that i’ve made recently. one of them even looks halfway professional
- Comment on Walls within walls 3 weeks ago:
This is why i always place all important info in Supplementary Information which is almost always free of charge. except on sciencedirect. fuck them
