skillissuer

@skillissuer@discuss.tchncs.de

• ⁨Comment⁩ on ⁨Single stub tuning for nonresonant UHF antenna⁩ ⁨⁨1⁩ ⁨week⁩ ago⁩:

  Check first on a smith chart whether transmission line that you can easily make or get and adjust its length has proper impedance for both source and antenna. The shorter length matching section has, the wider bandwidth you’ll get. There are typically two solutions, of which one is better. Ideally you’d like to have transmission line impedance a bit lower than what would be needed if only transmission line part was used (without stub)

  If you want to make a yagi, or mount antenna close to a mast and don’t care particularly hard about extremely uniform coverage, you can modify impedance by changing distance to reflector. If you want to use something like this www.wa5vjb.com/yagi-pdf/cheapyagi.pdf then this antenna (radiating element) is already unbalanced and doesn’t need balun that badly

• ⁨Comment⁩ on ⁨Single stub tuning for nonresonant UHF antenna⁩ ⁨⁨1⁩ ⁨week⁩ ago⁩:

  I don’t know if you need common current mode choke like this, it’s probably overkill, popping 3-4 ferrite beads on normal sized coax should be enough. Some people don’t even use it at all and things still work for them. You can also always use folded balun or sleeve balun as a common mode current choke. This toroid is only 20mm in diameter or so, and RG174 has minimum bending radius 6mm, so it’s abused a bit but not that much. It’s probably good for lower bands like 6m too. Alternative is to use a pair of twisted wire in parallel (these have 100 ohm impedance or so, two in parallel are closer to 50) wound on ferrite (more common on HF), and if size restrictions exist, you can use tall and narrow non-split ferrite bead instead of wide and short toroid like this one i’ve used. Also i made it this way because that’s what i had in my drawer. Maybe it was not balun that was narrowband, but radiating element is a limitation instead?

• ⁨Comment⁩ on ⁨Single stub tuning for nonresonant UHF antenna⁩ ⁨⁨2⁩ ⁨weeks⁩ ago⁩:

  that’s RG174, there’s only 25cm of it or so, so loss is probably not a huge concern (53dB/100m at 400MHz, so 0.13dB), and that common mode choke is probably a bit too much anyway

• ⁨Comment⁩ on ⁨Single stub tuning for nonresonant UHF antenna⁩ ⁨⁨2⁩ ⁨weeks⁩ ago⁩:

  not much? i don’t have scale but 150g perhaps? i think that if you don’t need it waterproof then you can just extend wires, use them for support and get rid of case entirely. this would require sturdier shorting bar and some spacers probably but would be more compact

  it’s 80cm long and can’t be folded, so if that’s portable enough for you, then yes

• Single stub tuning for nonresonant UHF antennadiscuss.tchncs.de ↗
  Submitted ⁨⁨2⁩ ⁨weeks⁩ ago⁩ to ⁨amateur_radio@lemmy.radio⁩ | ⁨7⁩ ⁨comments⁩
• ⁨Comment⁩ on ⁨If u use a SWR meter u vibe checking ur antenna⁩ ⁨⁨1⁩ ⁨month⁩ ago⁩:

  okay i see now

• ⁨Comment⁩ on ⁨If u use a SWR meter u vibe checking ur antenna⁩ ⁨⁨1⁩ ⁨month⁩ ago⁩:

  but what if you put another split ring inside it, it’ll be different

• ⁨Comment⁩ on ⁨If u use a SWR meter u vibe checking ur antenna⁩ ⁨⁨1⁩ ⁨month⁩ ago⁩:

  this is just small-ish magloop

  i’ve seen some people make magloops out of bike rims, it’s similar sized. the smaller it is the lower radiation resistance, higher currents and voltage on capacitor, narrower bandwidth, and lower efficiency. i don’t remember how it scales but efficiency goes up fast with size, 1m dia magloop is already better. downside is that tuning becomes impossible on higher bands

• ⁨Comment⁩ on ⁨If u use a SWR meter u vibe checking ur antenna⁩ ⁨⁨1⁩ ⁨month⁩ ago⁩:

  will it antenna? i think it will

  split ring resonator has already two different lengths of paths so - even without accounting on how these two interact - you could expect two different frequencies where it’s resonant, with peaks perhaps overlapping to a useful degree making a decently wide band possible. it looks a bit like halo antenna with parasitic, downside being that it’s probably a bit hard to feed it, circumference has to be halfwave on lowest frequency and if made for HF it’d be gigantic

  i think it’s more useful to think of magloop as extremely shortened, low impedance, low bandwith halo antenna

• ⁨Comment⁩ on ⁨What's so important about keeping military operations secret?⁩ ⁨⁨1⁩ ⁨month⁩ ago⁩:

  Another good example would be actions Brits took in order to protect the fact that Enigma was broken. For example, when Enigma deciphering indicated that there’s warship in a specific area, they would send spotter plane first before attacking it, in order to provide enemy alternative explanation as of how they were discovered. Some operations were aborted entirely for this reason

• ⁨Comment⁩ on ⁨ARMADILL-NO⁩ ⁨⁨1⁩ ⁨month⁩ ago⁩:

  I hear that this happens sometimes, but nowhere near normal times, more like during evacuations from warzone and so on

• ⁨Comment⁩ on ⁨Why don’t wireless connections (WiFi, Bluetooth, etc.) use anything between 2.4Ghz and 5Ghz?⁩ ⁨⁨1⁩ ⁨month⁩ ago⁩:

  sorry for being unclear, i forgor a word. what i meant that certain antenna designs would have specific fractional bandwidth, so that just scaling that design to higher frequency makes usable bandwidth wider in kHz terms. in order to get higher fractional bandwidth more complex or bulkier designs would be required, like thicker conductors, added parasitics, something LPDA-shaped, or maybe elaborate matching circuit, all of which cost money. i guess that while resonant amplifiers are a thing, probably bigger limitation would be bandwidth of mixer

• ⁨Comment⁩ on ⁨Why don’t wireless connections (WiFi, Bluetooth, etc.) use anything between 2.4Ghz and 5Ghz?⁩ ⁨⁨1⁩ ⁨month⁩ ago⁩:

  i’d also note that antennas, amplifiers and so on have bandwidth that is some % of carrier frequency, depending on design, so just going up in frequency makes bandwidth bigger. getting higher % of bandwidth requires more sophisticated, more expensive, heavier designs. LoRa is much slower, caused by narrowed bandwidth but also because it’s more noise-resistant

• ⁨Comment⁩ on ⁨Why don’t wireless connections (WiFi, Bluetooth, etc.) use anything between 2.4Ghz and 5Ghz?⁩ ⁨⁨1⁩ ⁨month⁩ ago⁩:

  what’s fixed service in this context?

• ⁨Comment⁩ on ⁨Has modern technology made espionage easier or more difficult?⁩ ⁨⁨1⁩ ⁨month⁩ ago⁩:

  Both got much more interesting. Also, don’t underestimate modern encryption

• ⁨Comment⁩ on ⁨What are some slow acting poisons?⁩ ⁨⁨1⁩ ⁨month⁩ ago⁩:

  cyanide doesn’t accumulate, it can be broken down in some hours. otoh many heavy metals do behave this way, maybe you worked with both at the same time

• ⁨Comment⁩ on ⁨What are some slow acting poisons?⁩ ⁨⁨1⁩ ⁨month⁩ ago⁩:

  all metals that bind to sulfur well are to some degree poisonous. these are lead, mercury, thallium, some platinides (in salt form), arsenic, and also copper, but less than others. some metals have other mechanisms of toxicity, like nickel, hexavalent chromium, cadmium, beryllium or barium. some of these accumulate in brain or bones, and some don’t. some are more toxic when inhaled like zinc or chromium

• ⁨Comment⁩ on ⁨What are some slow acting poisons?⁩ ⁨⁨1⁩ ⁨month⁩ ago⁩:

  it’s absurdly easily detected and somewhat easily treated today, not in op’s setting

• ⁨Comment⁩ on ⁨What are some slow acting poisons?⁩ ⁨⁨1⁩ ⁨month⁩ ago⁩:

  ah yeah the subtle, slow acting poison, the checks notes atropine

  all of these except one work on nervous system which means that they act rapidly. this is worse than nothing

• ⁨Comment⁩ on ⁨What are some slow acting poisons?⁩ ⁨⁨1⁩ ⁨month⁩ ago⁩:

  en.wikipedia.org/wiki/Amanita_phalloides

• ⁨Comment⁩ on ⁨"Americans can't coo-"⁩ ⁨⁨1⁩ ⁨month⁩ ago⁩:

  Image

• ⁨Comment⁩ on ⁨Is it possible to design a (pen and paper) cipher that is secure against government cryptanalysis for at least 10 years?⁩ ⁨⁨2⁩ ⁨months⁩ ago⁩:

  You can do RC4 on pen and paper, more precisely 256 pieces of paper. There’s also a variant of this cipher that uses deck of cards instead, RC4-52. There’s also another stream cipher that uses deck of cards to store state and it’s called Pontifex/Solitaire. Both have some weaknesses

  VIC has way too short key for modern uses, but maybe there’s a way to strenghten it

  On related note, i guess that it would be possible to implement modern stream cipher with NLFSR in electromechanical machine, no silicon needed. WW2 era cryptography like this (enigma, M209 etc) were in a way stream ciphers and these require some of least hardware. Key storage and scheduling becomes bigger problem

• ⁨Comment⁩ on ⁨What happened to cylindrical plugs?⁩ ⁨⁨2⁩ ⁨months⁩ ago⁩:

  you don’t see BNC as often because it’s more expensive, bulkier, requires different crimping tool and has a separate pin. but if you need to connect and disconnect things often and quickly, then it’s a good connector. i bet you’ve seen (RP-)SMA a lot instead, but this one is also more expensive than F, has separate pin and is too small to easily make a connector for common 75 ohm cables. reducing diameter would mean higher loss

• ⁨Comment⁩ on ⁨What happened to cylindrical plugs?⁩ ⁨⁨2⁩ ⁨months⁩ ago⁩:

  i keep hearing that F stands for Flimsy. no idea where that came from, unless something is seriously wrong with crimping technique. i guess there’s a tradeoff between CCS or copper cable with durability of pin/center conductor vs bending radius, and some people don’t like how it turns out, while ignoring that it’s cheap and not really designed for multiple disconnections

  but yeah, as long as everything is matched good-enough then it’s a cheap way to connect low loss, cheap cable

• ⁨Comment⁩ on ⁨What happened to cylindrical plugs?⁩ ⁨⁨2⁩ ⁨months⁩ ago⁩:

  The context of the whole thread, though, was end-user, repeated, frequent connections for people who have to be reminded by a manual that the thing needs to be plugged in. Coax is horrible for that.

  so you want BNC

• ⁨Comment⁩ on ⁨What happened to cylindrical plugs?⁩ ⁨⁨2⁩ ⁨months⁩ ago⁩:

  power plug with 3 wires or 5 wires (3-phase) could be made safe-ish if there was a button at the very end that connected to a relay or something. but plug like this would be comically long for any practical power

• ⁨Comment⁩ on ⁨What happened to cylindrical plugs?⁩ ⁨⁨2⁩ ⁨months⁩ ago⁩:

  i don’t think you’re supposed to hotplug soldering iron tip. besides it’s a simple thing, isn’t that just two resistors - one for heating element and another for measuring temperature? hard to break that. not sure about how ipod shuffle worked or what precautions were needed

• ⁨Comment⁩ on ⁨What happened to cylindrical plugs?⁩ ⁨⁨2⁩ ⁨months⁩ ago⁩:

  Coax has only 2 conductors and it keeps impedance constant, unlike audio jack

• ⁨Comment⁩ on ⁨What happened to cylindrical plugs?⁩ ⁨⁨2⁩ ⁨months⁩ ago⁩:

  There are two immediate problems with round USB. First one is that audio jack carries no power and it’s generally rather harmless for finals or microphone to have some contacts shorted or crossed for time when plug is inserted. USB, let’s even just 4-pin, carries power and i’m not sure how well would either of devices react to having data bus connected to +5

  The other problem is that USB is proper radiofrequency connector, unlike audio jack where anything goes. This means it has to be shielded and impedance has to be some specified value, which in practical terms means that there’s some specific ratio of metal to plastic and shape of conductors that has to be used. Barrel plugs would have way too low impedance and already bulky connector needs extra shielding which makes it even bigger

• ⁨Comment⁩ on ⁨Antenna Recommendations⁩ ⁨⁨2⁩ ⁨months⁩ ago⁩:

  antenna making is art of tradeoffs. there are different ones between size, cost, weight, mechanical and electrical complexity, wideband performance, radiation pattern, efficiency, and use of harmonics if any.

  for VHF and up, it only makes sense to make single band antennas because cost and size savings are tiny otherwise, but bandwidths are large and there are no reasonable autotuners. there are special cases such as 2m/70cm antennas that can do both, but that’s it. this is area of simple or folded dipoles, halos, yagis, LPDAs, helical antennas, and in bigger end of scale antenna arrays and optical-like systems like parabolic reflectors

  for HF, if you have budget and real estate for it, some of best antennas money can buy would be LPDA for entire range you’re interested in. this thing, however, for 3-30MHz range would be a giant aluminum triangle 40m wide, 50m long, weights well over a ton and needs mast and rotator because it’s directional, not to mention that it costs fortune. but on balance it can reject noise from wrong directions and is always matched

  some typical approaches are as follows:

  1. single band wire antennas. these would be halfwave dipoles in any shape (straight, inverted-v, slopers, off-center and so on), j-poles, groundplane antennas, quarterwave dipoles (requires good ground) and couple other variations. these are light, cheap, efficient, fit entire single band without gross abuse of finals, have uniform radiation pattern. but only on one band, and having multiple of them in proximity can lead to weird effects, so these are best if you’re hiking for example, but good in general

  2. principally single band wire antennas but now we also want to squeeze some other bands out of it. these are dipoles - normal or OCFDs, full wave loops in one approach and trapped dipoles in other. in first case, we exploit the fact that there are usable harmonics on some bands - 80m has 40m, 30m, 20m, 17m, 15m, 12m and 10m. 40m has 20m, 15m and 10m. 20m has 10m. but depending on type not all are always usable and higher harmonics will have narrowed usable band compared to single band case. in trapped dipole approach there’s a limit on how many traps you can put (mitigated to some degree if you make it asymmetric and put traps on one side only), and as traps work as coils, these shorten antenna which also narrows usable bandwidth but now for lower bands, opposite of the former. use of autotuner and low loss transmission line can make it work over wider bandwidth, but this only goes so far. note that some bands are narrower than others (12m, 17m, 30m, 60m) and it can be made to work for these pretty well, but less so for others (80m, 40m, 20m, 15m, 10m), but it can still work if there’s less bands on one antenna, especially if you’re not interested in entire band (like for CW-only or voice-only operators), are willing to accept some loss of power, or use tuner, or combination of some of these

  3. antennas that are by themselves not resonant at all. these are either lossy (like terminated dipole) or require tuner, sometimes purpose-built and can be narrowband when tuned (doublets, magloops) both can be reasonably compact. because match lies in tuner, these are multiband by virtue of changing tuner settings. terminated antennas have good match but also you can be dumping half of power or more in resistor. there are also ways to use mast antennas in this way, even if they are grounded (using gamma-match for example)

  4. antennas that have to be extensively electrically shortened because wavelength is huge. these are generally everything from 160m down. these are things like magloops and bespoke wire antennas with loading coils and capacitive hats and such. because these are short in comparison to wavelength, efficiency is small and bandwidth is tiny (but can fill entire band) but also require extensive space just due to how huge wavelength is

  5. some directivity can be achieved by making yagis (higher part of HF) or by deploying multiple antennas in an array. depending on band and type of antennas this can get very elaborate and expensive. simplest and cheapest way uses multiple radiating halfwave elements connected by coils, or with parallel parasitic elements. this can get decently directional while also being a bit compact but also this makes it more narrowband and due to large size only makes sense for higher HF and VHF

  but start simple. single band wire dipole or j-pole would be probably best in your situation