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Where I live we have signs up all over the place near the mountains that tell you to tune into a specific AM station when flashing for avalanche/weather informa
by galleywest200 2y ago
Where I live we have signs up all over the place near the mountains that tell you to tune into a specific AM station when flashing for avalanche/weather information. I understand wanting to move past some technologies but we are not going to be able to revamp our entire avalanche system _tomorrow_.
Most people I know do not have a short-wave radio, let alone one capable of receiving at 162Mhz.
- tomjen3 2y agoWhy not broadcast it as FM? Much better signal, much less chance that somebody misses a word because AM quality is shit.
- aragilar 2y agoAM covers a larger area, and is more robust in areas with obstructions (e.g. mountains).
- TylerE 2y agoYeah, I remember as a kid with a Cheap stereo and an antenna consisting of maybe 5ft of thin wire dangling from it being able to pick up reasonably clear AM transmissions from as far away as St Louis, Chicago, and NYC… and Inlived in almost-coastal NC. Especially at night you could really pull some stuff in. FM by comparison is effectively line of sight, so with a practical broadcast antenna the upper limit is 40 or 50 miles.
- kragen 2y agothe am antenna in your cheap stereo was probably not the dangling wire, but rather a ferrite rod hidden inside the case
- TylerE 2y agoPretty sure it was the wire, because changing how it was aligned would affect what could pick up pretty dramatically. And I should clarify… while it was certainly a cheap “system in a box”, it was a real multi component system with detachable speakers, etc. not a boombox or anything like that.
- lebuffon 2y ago"AM" is the modulation scheme. A more accurate name for this radio service is used in Europe, "middle-wave". The modulation scheme is not the reason for propagating around mountains and bouncing off the ionosphere at night. The reason for that behaviour is the low frequency used. 540 Kilo-herz to ~1700 Kilo-herz. (I was told once by a young engineering colleague that 1,000 Khz was not RF. :-))) ) So the question is valid. FM could be used in the "middle-wave" band. It would reduce noise but might suffer more when bouncing off the ionosphere at night. (I have read this but never heard FM bounced) The reason FM is not used in the middle-wave band is legacy regulation not technology.
- ikiris 2y agoFm also takes 10 times the bandwidth of am of that spectrum. The blocks are where they are for a reason.
- lebuffon 2y agoFM takes whatever bandwidth you allow it. The harder you hit it the wider it goes. The limiting factor is when modulation exceeds the bandwidth of the receiver, it clips very badly. Narrow band FM is used for aircraft. police, fire, amateur radio communication and since 2021 it's even legal for CB radio in the USA. It's deviation is limited by law to about +/-2.5KHz, from centre frequency. Setting up the modulation depth on an a broadcast FM exciter, I have used a spectrum analyzer and Bessel function information to make sure it was legal.
- hilbert42 2y ago" (I was told once by a young engineering colleague that 1,000 Khz was not RF. :-))) )" I've alluded to this elsewhere. As I mentioned, RF/RFI and spectrum management subjects have been downgraded or reduced in electrical engineering courses just about everywhere so it's little wonder we've problem.
- Aloha 2y agoBandwidth in part. AM is more spectrally efficient than FM, and with synchronous AM receivers, you can get noise rejection that is near FM.
- TeMPOraL 2y agoNoise reduction in this scenario would be performed the obvious way - by looping the message.
- cloudwalk9 2y agoI THINK it is FM, narrow FM. My SDR receives some attenuated incomplete-sounding signal when switched to AM on 162.55 MHz even if I widen the bandwidth, and switching to narrow FM gets me the same clarity and volume as my actual weather radio provided I lower the gain a little.
- ac29 2y ago162MHz is VHF, shortwave is much lower frequency (and longer wave). More or less all US car owners already own a VHF radio. Extending it from 88-108MHz up to 162MHz would be fairly trivial.
- katbyte 2y agoRetro fitting all previous car & upgrading all am based equipment is not however
- gopher_space 2y ago> Where I live we have signs up all over the place near the mountains that tell you to tune into a specific AM station when flashing for avalanche/weather information. I live in an area like that as well, and the station broadcasts the same info you see on road signs and web sites. If the lights are flashing it's usually playing "snow tires advised for vehicles..." on loop. the kind of situations people describe where car AM radio is essential feel like corner cases that involve lack of planning and poor judgment or really bad luck. No cell service, no portable radio in your travel kit, no way to stop and ask anyone, and you can't just turn around when you see a flashing sign? It sounds like the plot of a horror movie.
- katbyte 2y agoThat’s YOUR area. Plenty around here without any giant flashing signs. Also long 100km bits of highway without cell service Thing about corner cases is they do exist and need to be accounted for
- herewulf 2y agoSo, cars in YOUR area should have AM radios? But not every car in existence needs one?
- deleted 2y ago[deleted]
- gopher_space 2y agoIf you actually lived out in the country you'd know that there's like a dozen portable AM radios per household and that nobody ever just guesses about pass conditions. Every scenario people come up with involves a hypothetical hayseed who's almost aggressively unprepared for his situation. This is a problem solved by a $10 Amazon purchase. Why is it such a crisis for you?
- cloudwalk9 2y agoPersonal anecdote: that actually saved an important doctor appointment. "URGENT MESSAGE WHEN FLASHING". Well, lights were flashing, guess we could tune to it and hear what it has to say. Sure enough, it announced a traffic jam on our route a few miles ahead that Google Maps vastly underestimated (usually it's been good about that) and we were able to avoid it. Thanks TNDOT. It was because a chemical truck crashed apparently, on our drive back home it was still there with specialized hazmat emergency vehicles around.