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Jonny 290 posted:I still keep a roll of waxed cotton line around and do old school cable lacing when i can. This is kinda what i was thinking about. What i expect to run into when using a tunable oscillator, is that i need to figure out a way to tune the output stage too. I have no idea yet if the antenna tuning and output filter setup is 'coarse' enough to cover 1810-1890kHz (my country's band limits for 160m). I think it might just work. Being able to do digital modes also extends range a bit. On sea water, the expected range is 40-60 mile, but on land the range will probably one tenth of that in AM voice. LimaBiker fucked around with this message at 11:29 on May 4, 2023 |
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May 4, 2023 11:27
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| # ¿ May 13, 2024 01:14 |
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It's fairly easy to build a magloop-based setup that you can use for very local real time communications. I once threw together two 1m diameter loop antennas, with a TDA2003 based oscillator (those things oscillate very happily as they are, let alone if you actually try and make them oscillate!) and i already had a range of about 50 meters with a receiver that was bad enough to not even be able to receive SAQ (in the Netherlands where their signal is pretty strong). I reckon i could build something that'll have a range of 1km or so with a 2x2m square magloop and a better receiver. But it's kinda not legal. I'd love to see an extra amateur frequency, for instance 17,0 and 17,4kHz (with 17,2, SAQ's fixed frequency, as a secondary allocation as to not interfere with their broadcasts) so the really ambitious hams in the Scandinavian countries could attempt a QSO with SAQ. If you're not going for real time communications but for very slow digital modes, you can use 8997Hz legally (cause it's below any radio frequency allocation). Check out https://sites.google.com/site/sub9khz/
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Sep 8, 2023 15:46
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Try it.Though 100w is a lot for a random wire, and it comes with interference risk. Whether it's a fire risk or not depends completely on the band. If it happens to be a half wave antenna, the high voltage point will be near or at the feed point, and that's generally where you can deal with the voltages. At the point where current is high but voltage is low, there'll be no fire risk and the least amount of influence by branches. If for some reason that high voltage point is shifted towards the spot where you have branches (for instance if you end load the wire with some kind of extra capacitance - that's not something people typically do for a random wire but it might just help you extend the usable frequency range down), you can have arcing in other locations. A healthy tree won't be bothered by that, but dry leafs and wood could theoretically be ignited by it. As for the influence - just do it. A poo poo antenna is better than none at all. Consider running the wire in a thick walled RF transparent plastic pipe if you're very worried about the arcing risk. You can also just try it out on a day that the tree's wet. Intentionally push a branch against the wire, see if you get arcing or steam. It'll detune your antenna but most modern rigs are protected against weird SWRs LimaBiker fucked around with this message at 19:48 on Sep 22, 2023 |
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Sep 22, 2023 19:41
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First, establish who you want to contact. How far away are they? Will they be listening? What do you want to contact them for - will they be able to get you what you want? Whatever you decide, be aware that the first thing you need to do when you want to get into emergency communications, is to organize. Just screaming 'help' into your microphone and hoping for the best... Well, you can be lucky if people on CB still listen to CH19 in emergency situations, but i honestly have no clue what people do on CB when it comes to emergency stuff. ARES (for ham radio operators) has a big focus on the organisation stuff that you need in emergencies. In short: handheld CB radios with their stock antenna are only usable for local communications within a handful of kilometers. If you only want to talk to friends on the other side of town, it's useful. Otherwise not. However, if that's your goal, you might already be able to do that with PMR446 UHF handhelds with 0,5w of power that are much lighter and more energy efficient. If you connect the handheld CB you are considering to a proper antenna, you can expect a range of 45km with legal power over flat terrain. However, a proper antenna is either 2,5m long with a bunch of radials hanging under it, or 5,5m long with no radials to speak of. Or a dipole with a total length of about 5m. If you are willing to go the illegal route, a 25w amplifier and a good quality car mounted antenna will also get you about that range. In my country no one gives one single gently caress about what you do on CB power wise, but my country isn't your country so proceed at your own risk. CB is better over rough/hilly terrain than VHF and UHF. Good range with CB equipment means long antennas that will snap off in a hurricane - so you need to make an expendable wire antenna to listen out for other people in emergencies, while keeping your good antenna inside to deploy when you need it. Pre-tune it, mark all the tuning positions so you can easily set it up again. By now you might realize that CB stuff can be cumbersome. But it's the only long range option for license-free communication. Now, if you want to get your ham license, you can literally get the same flat terrain range with a handheld and a whip antenna that you stick out of your house's attic window or whatever. A basic 144mhz half wave vertical can go dozens of kilometers, which means you can probably access a repeater and cover even more area. In the mountains, you'll need to resort to longer wavelengths again to bounce your signal off of the ionosphere. Which means large antennas, though with modern digital text modes you can already do a LOT with just a magloop of 1 or 2m diameter. But in the end, it's all about what you want exactly. If you want the emergency services to come and help you, a satellite phone or one of those satellite text message things might be more what you're looking for. If you want to just stay in touch and talk to people while power's down and everything's hosed, radio might be a good option. LimaBiker fucked around with this message at 17:42 on Sep 30, 2023 |
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Sep 30, 2023 17:39
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Your RF ground doesn't even have to be a DC/LF path to earth. A counterpoise can be isolated from earth, yet be completely functional. If you use a grounding rod for RF, you could use a high quality capacitor, suitable for handling RF current, to make sure you only have 1 mains safety ground. You might want to insert a choke of some sorts into your mains earth, at the transmitter side. You can use a 1M resistor to shunt static electricity to ground. Grounding transmitters is loving weird. When i was testing my Yaesu FT101 (100w) at the seller's place, we set it up on a kitchen counter, with the radio and the dummyload (with grounded metal case and a fan) both in a grounded outlet. After testing for a while, the dummyload's mains ground wire started to smoke. For that to happen, you need to run like 30-40 amps through it. The isolation of it was completely wrecked and both me and the seller were completely puzzled. At first i thought that the radio had a bad ground fault and the guy's GFCI wasn't working (and the fuse didn't pop in time). But i checked all of that stuff and it was fine. Something must have worked as a RF transformer. Years later i had a similar thing happen but with the connection between my antenna tuner ground and the central heating system's radiator/metal tubes (convenient thing to ground small transmitters to, it's a nice big mass of iron). Nothing else got even close to getting hot. Tuner cold, mains cable to the transmitter cold... So yeah, take care, especially if you run high power.
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Nov 9, 2023 17:39
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Okay we need a digimode now that literally sounds like farts but actually has data/text encoded in the flatulence. I suggest we call it Flatulencia.
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Mar 6, 2024 23:04
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I would blow Dane Cook posted:Does this Aurora do anything to radio signals? My GPS accuracy was unusually lovely today. Google Maps tries to lock me to the nearest road - it locked me to one a couple hundred meter away for quite some time, with no obstructions around anywhere.
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May 11, 2024 17:34
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| # ¿ May 13, 2024 01:14 |
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The Web SDR from the university of Twente, the Netherlands, captures full day waterfall displays of the entire 0 to 30MHz frequency range. You can now visually compare the propagation of a normal friday-saturday-sunday, versus the one we just had with a big solar storm. Check it out here: http://websdr.ewi.utwente.nl:8901/fullday/ It's a very wide graphic, might wanna zoom all the way out.
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May 12, 2024 08:41
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