fullsquare
@fullsquare@awful.systems
- Comment on Made some J-poles 12 hours 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 22 hours ago:
Paging @tasankovasara@sopuli.xyz for logistically efficient antennas
- Comment on Soldering 20m and 40m low pass filters from QRP Labs for RPi WSPR 22 hours 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 22 hours ago to amateur_radio@lemmy.radio | 3 comments
- Comment on Making a 1:1 Balun for Amateur Radio 1 day 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? 1 day ago:
- Comment on My try for an apocalypse radio 1 day 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 2 days 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
- Comment on My try for an apocalypse radio 4 days ago:
i’ve seen someone made rollup j-pole on basis of fabric strip, with conductive fabric strips sewn on. so you could probably take an actual flag and do the same, because yagi elements need some thickness and flat strips are good enough. this looks a lot like yagi printed on pcb board, except that pcb board is stiff, and you’d need some rods to stretch the fabric. so there already is need to store long sticks. instead, you can make a regular yagi but with elements that can be detached when not in use. i bet somebody made 3d-printable clamps like that
there are commercial antennas available, but you will pay an arm and leg
- Comment on My try for an apocalypse radio 4 days ago:
that’s good, we’re not starting from zero then. take note that some solutions that work for 27mhz band don’t work on vhf/uhf, mostly balun and impedance transformer construction. HF baluns use multiple turns of coax or twisted pair through ferrite, on VHF and up it’s better to use single turns (ferrite beads) or transmission line baluns (folded balun or sleeve balun). it’s also more practical to use some form of transmission line impedance transformers (like quarterwave matching). on vhf and up lumped element tuners are not really a thing, antennas are much smaller so they’re just made to match
The particular antenna I was asking about is something I couldn’t DIY
i’m not familiar, if you could describe it in some more detail that can be probably figured out
for 70 cm, i’ve suggested jpole because it’s compact (long and thin), you can probably package it in 30mm or smaller plastic pipe, haul it around, pull out and mount it with a clamp on top of (not parallel to) metal mast and be good to go. you can have metal mast couple cm below shorting bar of jpole, or even a bit away and parallel to for a short run and it shouldn’t matter. if needed, radiating part can be mounted parallel to metal mast but needs to be a good distance away (halfwave away or more unless you want to tune it in place). with nonconductive mast the only conductor nearby is coax. it would be 50cm-ish long so good for mobile setup. these are fast and cheap, the way i’ve made them the most expensive part was plastic box, can be made and tuned with nanovna in a single evening
groundplane antennas would be even shorter but much bulkier, unless you detach radials or mount them on a kind of swivel mount, and you have to put them in the air, as in, bottom end of radials can’t be too close to ground. mast considerations are pretty much as jpole, as in, the hub can be mounted on top of metal mast but not parallel and right next to it. if folded, 2m version would be about 50cm long, so it’ll probably make sense on 2m and down. you can probably make a 70cm band quarterwave whip attached to magnet so that you can put it on roof of your car, but it won’t be as good because height is might here, and jpole has center of radiation half wave above mounting point just because of the way it’s built. just that little bit of extra height might clear some obstructions. straight dipoles should also work, but they’re T-shaped unless disassembled, and you’ll have to run coax perpendicular to dipole for some length to avoid common mode current problems -> not as simple mechanically, fine for horizontal not so much for vertical
you could also make a small (5-7 el? depends on how long do you want it) 70cm band yagi and store it on top of your radio box, but you’ll need to put it on a mast then rotate it, or hold it in your hand, preferably standing on a hill or something when in use. stiff jpole would be probably fine for 70cm, 2m if you can accommodate the length, lower than that, 2m to probably down to 6m or 10m, rollup jpoles should work okay as long as you have a way to deploy them. below that it’s probably mast + some kind of halfwave dipole territory (efhw? doublet? series of center fed dipoles? ocfd? some type of vertical? you decide)
- Comment on Making a 1:1 Balun for Amateur Radio 5 days ago:
You have to keep in mind to not exceed coax bending radius. Solid insulator (as in not foam) coax works better
I’ve seen people using twisted pair of enameled wire (50 ohm) instead, or a pair of insulated twisted wires connected in parallel (each is 100 ohm impedance) this allows for much tighter turns. This works only for HF, for VHF and up there are alternatives and multiple turns don’t make sense, it’s better to use ferrite beads
- Comment on My try for an apocalypse radio 5 days ago:
antennas are on the more diy-able end of this activity, no need to buy them, make your own. firestik is a cb band (27mhz) antenna so you can’t use it anyway for this (your radio can’t transmit there either). you’ll need a way to measure your antenna, which means you need a tool like nanoVNA. for 70cm band, j-pole antenna will be easy to make and compact (50cm ish long) and would be either stiff (made from small diameter copper or aluminum pipe/wire) or elastic (so that it can be rolled up). if the former, put it all in a pvc water pipe sealed on both ends, with coax output going through a cable choke, or put the bottom section (from feedpoint to shorting bar) in some kind of plastic box, with wires also going through cable chokes. note that when tuning, pipe needs to be on antenna, because enclosure will shift resonant frequency down. you can mount the enclosure with metal clamp to something as long as clamp is below the shorting bar at the bottom. if latter, use twin lead for the parallel line section, or make your own because it can be hard to get (like this) aim for 300-450 ohm impedance. then you can roll up this antenna when not used and suspend it from a fishing rod (wood or fiberglass only) or from string attached to tree or something when you need to use it. in either case, do not connect shorting bar to coax shield and do put a ferrite bead or two on coax. do not deploy antenna directly next to conductive surface or rod. do not deploy antennas next to power lines. if you want to use 2m band, you’ll need separate, 3x longer antenna for it. there are slightly more complicated ones that get you both 2m and 70cm. there are many guides about this, but this is one of simplest ways to get it working
that said, you’ve got a pretty capable, heavy and expensive radio here. if you just want to use 70cm, then you can get away with something much smaller and cheaper, you could hold it in your hand. like baofeng, or quansheng if you want to reflash it. 70cm (UHF and VHF in general) allows for contacts within line of sight only; put your antenna on a mast for more range. HF bands have different limitations, but range is not limited in this way (it’s limited in different way). there are many schools of thought on how to make it work best, but general shape of solution is either halfwave-ish long reel of wire (low tens of meters) that needs to be put high in the air, horizontally, either using trees or fiberglass mast as a support, or some kind of conductive mast (or nonconductive mast with wire going up along), about quarterwave long, with wires of similar length strewn on ground. there are many choices and tradeoffs depending on where you intend to transmit from (car? bike? some mobile setup with everything fitting in a backpack? shed in the woods? tent in the desert?), target bands (HF or VHF/UHF or maybe microwaves?) and how are these supposed to be used (CW? phone? digital modes? point to point contacts? through repeater? through satellite? bouncing signal from the moon?)
- Comment on Built a bulkhead to bring antenna coax into my office 1 week ago:
You can cut open and flatten a bit of wide (1”?) copper pipe to get a piece of copper sheet for grounding, if you can’t get it otherwise
Is there one bulkhead or two, and if one, how will you attach third and fourth cable?
- Comment on SpaceX stock tumbles 16.4%, shaving off most IPO gains since debut 2 weeks ago:
still 84% to go
- Comment on [deleted] 3 weeks ago:
you’ll be lucky until you aint, then you’ll get banned for ban evasion
- Comment on is it spelled "grey" or "gray"? 3 weeks ago:
grey - 🇬🇧 english (traditional)
gray - 🇺🇸 english (simplified)
- Comment on [deleted] 4 weeks ago:
not sure but excessive caffeine can definitely make it worse
- Comment on How much did drug test cost back in the day? I just took one from an independent drug test guy and he does them at 45 dollars per person and earns about 15k a month. Y wasn't the done sooner? 4 weeks ago:
i mean technically it’s possible, you can show someone lab i guess there’s nothing extremely dangerous, not sure how it works legally, but the process is rather boring and we’re talking about a place that stores literal tons of piss why would you go there
- Comment on How much did drug test cost back in the day? I just took one from an independent drug test guy and he does them at 45 dollars per person and earns about 15k a month. Y wasn't the done sooner? 5 weeks ago:
what kinda drug tests are we talking about here? i’m talking about the kind where you send piss sample and then get result, or in fact hundreds of results. you need to make sure all your paperwork is complete and lab is certified and so on because someone might say that results are legally invalid
- Comment on How much did drug test cost back in the day? I just took one from an independent drug test guy and he does them at 45 dollars per person and earns about 15k a month. Y wasn't the done sooner? 5 weeks ago:
to run drug tests you need six figure range machine, maybe 5 euro worth of plastic (spe column, eppendorfs, pipette tips), couple ml of acetonitrile and maybe 10min of machine time. it can run 24/7 and if you find anything you can do more detailed analysis
- Comment on This figure illustration from an article on AI sycophancy and human behavior is the epitome of 2026 1 month ago:
there was a time when anthropic models would refuse any question related to medicine. not because they care that hard, mind you. it’s because that bloated startup is ran by cultists and they were worried that chatbot will come up with a bioweapon
- Comment on All mixed up 1 month ago:
if you do that you have bigger problems
- Comment on All mixed up 1 month ago:
only if you take notes
- Comment on All mixed up 1 month ago:
this advice is specifically about sulfuric acid. it’s denser than water, so if added to it it will sink diluting itself along the way, while also heating water around and making it float to the surface. if done opposite way, water won’t mix immediately because of large density difference so neutralizatio heat will be deposited on surface between these two boiling water and throwing acid around. this matters less with other acids because less heat is deposited, and in some cases acid is less dense than water. but if you stir the acid quickly, you can do it either way as long as you control temperature. this also is the case when you need to mix two different acids
tldr you can do whatever you want as long as you know what are you doing
- Comment on Science is iterative 2 months ago:
technically pv panels are also heat engines. this is why they need cooling
- Comment on Science is iterative 2 months ago:
the steam part is in the rest of hydrological cycle
- Comment on load bearing worm 2 months ago:
seeing that jargon file has an extensive page on retrocomputing feels like figuring out that there were archeologists in ancient egypt
- Comment on load bearing worm 2 months ago:
some people would tell you that we can simulate small bits of chemistry but it’s flat out wrong (i might be biased as i’ve wrangled for a year with computational chemists about results that don’t conform to reality) and even then errors are so large that’s it’s useless
- Comment on what is this??? 2 months ago:
Pain
- Comment on load bearing worm 2 months ago:
and then some bozo says that biology is just complicated chemistry and chemistry is just complicated physics and we can simulate physics
curious thing is that i never hear biologists or chemists saying that, only some physicists and techbros. just trying to simulate your way out of small organic chemistry problems will make you even more hopelessly lost than you were before
