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Why Do FM Frequencies End in an Odd Decimal? (2015)
- SamReidHughes 7y agoThe article doesn’t say it explicitly, but it’s because the FM band is bounded by round numbers, 88 MHz and 108 MHz, as opposed to 87.9 and 107.9.
- deleted 7y ago[deleted]
- ac29 7y agoEr, that's in the first sentence. What could be said a little more clearly is that the frequency 90.1 is actually the channel 90.0-90.2 since the convention is to tune to the center frequency. A convention of tuning to the lowest or highest frequency of the channel would be equally valid - its just not how its done.
- jeffdavis 7y agoIf you tune to the lowest frequency in the channel, wouldn't that be bad because it's on the border with the channel just below it? Tuning to the center of the channel seems like the only sensible thing to do, it's not just a convention. Or am I way off here?
- baddox 7y agoI assume the convention applies to both receivers and transmitters.
- ac29 7y agoAll I mean is that in the modern digital world, there is no difference between a channel being defined as 90.0 + 200kHz, 90.2 - 200kHz, or 90.1 +- 100kHz. "Tuning" isn't even really a thing in modern SDR receivers that can receive a huge band all at once (it is, but more as a UI convention than an analog necessity).
- deleted 7y ago[deleted]
- gugagore 7y agoThis is probably just splitting hairs, but I don't think it is equally valid. Compared to the channel width, the center frequency is known / required to be set much more precisely. You could wiggle around by the bandwidth by 100s of Hertz and maybe lose some fidelity, or get some interference from neighboring channels, but you can't say the same for the center frequency.
- ac29 7y agoOnly by convention though. The radio systems I use have a configurable channel width and center frequency - there are only so many legal options. Center frequency is just a convention though - a 100kHz channel being defined as being bounded by (freq + 50kHz, freq - 50kHz) is no more logically valid than (freq, freq + 100kHz) or (freq, freq - 100kHz).
- gugagore 7y agoWhat I'm saying is that the filter that shapes the bandwidth (on either Rx or Tx) is not a brick-wall filter. The channel width isn't exactly as stated, because there's a gradual roll-off. If I misspecified the bandwidth, I can still tune into and broadcast at the right frequency. It's not just a convention, it follows how the transmitted and received signals are actually processed. I do not think it's more logical because setting the center frequency and setting the bandwidth of the baseband signal are two independent operations. Conceptually, they are orthogonal concepts. So it's logical to specify them in an orthogonal basis. Choosing another basis, as you're saying, works. But the current "convention" is more than just a convention. It's the natural choice. If I take my FM radio and take it somewhere that uses different channel spacing, I can still tune it to the advertised frequency. That would not be the case with what your proposing.
- jaywalk 7y agoIt used to be relatively common for FM radio stations to run at over 100% modulation because it would allow them to be "louder" than the competition. Obviously this is illegal because it results in "spilling over" the assigned frequency band. But it absolutely was a thing.
- reaperducer 7y agoWhat could be said a little more clearly is that the frequency 90.1 is actually the channel 90.0-90.2 Not strictly. The main channel is 90.1. But many FM stations have sideband channels for various audio and data services, like reading books and newspapers to the blind.
- SamReidHughes 7y agoAfter reading the whole article, I was still wondering why they didn't just put the center of the frequencies on the even numbers. Then I realized that's not the order in which they decided what to do.
- m-hilgendorf 7y agoSome of my favorite radio stations broadcast(ed) below 88MHz. 87.7 and 87.9 are favorites of college and low budget FM broadcast.
- drmpeg 7y agoMost likely a TV station. Known as "Franken-FM stations". https://en.wikipedia.org/wiki/Channel_6_radio_stations_in_the_United_States https://en.wikipedia.org/wiki/Channel_6_radio_stations_in_th...
- Neil44 7y agoHere in the UK you get stations ending in any decimal. Other countries have different schemes. It’s a thing when you import a car from Japan for example, the FM bands are different so you have to swap the radio or buy a little band expander box to fudge it. https://en.m.wikipedia.org/wiki/FM_broadcasting https://en.m.wikipedia.org/wiki/FM_broadcasting
- RachelF 7y agoIn the US, you only get 200kHz between stations, while other countries allocate 300kHz spacing, giving them slightly more bandwidth.
- anticensor 7y ago100kHz signal bandwidth+100kHz guardband actually.
- cbanek 7y agoAnother interesting note about the FM frequencies is stations from 88 MHz to 92 MHz are the non-commercial part. That's why you'll find a lot of NPR and religious stations at that part of the dial rather than the other end. (Looked up after many hours of road tripping through states with very few radio stations) https://en.wikipedia.org/wiki/Non-commercial_educational_station https://en.wikipedia.org/wiki/Non-commercial_educational_sta...
- anyfoo 7y agoWorth noting that that's not a thing in Europe, at least in Germany I don't remember any differences across the entire band (87.5 to 108 MHz there). Where exactly the band is and its channel spacing generally differs a lot between countries.
- closeparen 7y agoThis article is on the website of the US telecommunications regulator. I'm don't think all the comments need to be qualified with "in the US."
- mturmon 7y agoYour experience (listening to non-commercial stations on the left side of the dial while road-tripping) was memorably summarized by the Replacements in "Left of the Dial" -- https://genius.com/The-replacements-left-of-the-dial-lyrics https://genius.com/The-replacements-left-of-the-dial-lyrics
- _bxg1 7y agoSomething I've always wondered is where the channel "names" come from. The ones that are usually 4-6 characters, seemingly random, often starting with K or W for some reason. Like KVUE or W2XMN or KLTY.
- dlgeek 7y agohttps://en.wikipedia.org/wiki/Call_signs_in_the_United_States#Broadcasting_stations https://en.wikipedia.org/wiki/Call_signs_in_the_United_State...
- deleted 7y ago[deleted]
- drmpeg 7y agoThe term you're looking for is "call sign". K and W have been assigned to the United States. https://en.wikipedia.org/wiki/ITU_prefix https://en.wikipedia.org/wiki/ITU_prefix
- pansa2 7y agoThese seem to be commonly used in the USA - are they used elsewhere?
- anyfoo 7y agoPersonally haven't seen them anywhere else at least. While the stations might or might not have call signs on paper, they are certainly not used in any way a listener would notice. (Of course I can only speak for the countries I've been to.)
- reaperducer 7y agoIn Canada, you hear them all the time. Like CFOX/Vancouver, or VOCM/Saint John. In Japan, as well. JODW/Tokyo, and others. The only exception I've heard in Japan is Eagle 810, which operates from a U.S. military base.
- LeoPanthera 7y ago
- Aloha 7y agoits more interesting that FM stations have channel numbers, which are basically not used by anyone except the FCC.
- taneq 7y agoSame with analog TV stations, I never understood why they use specific ones. Why channel 7, 9 and 10 but not 8 or 6?
- drmpeg 7y agoAll the channel numbers are used. But in the analog days, channels were separated by market to reduce interference. One market would use 2, 4, 5 and 7 while the adjacent market would use 3, 6 and 8.
- yftsui 7y agoYeah its interesting why they are not widely used. Analog broadcast channels do have 6 or 8 though, https://en.wikipedia.org/wiki/Television_channel_frequencies#Americas_(most_countries),_South_Korea,_Taiwan_and_the_Philippines https://en.wikipedia.org/wiki/Television_channel_frequencies...
- Aloha 7y agosome places use channels 8 or 6. it just depends how many TV stations your market has
- deleted 7y ago[deleted]
- anyfoo 7y agoBy the way, in Europe, even for analog TV the channel numbers have been relatively hidden since at least the 80s. TVs would instead be "programmed" to have sequential program numbers, which behind the scenes pointed to actual channel numbers. The channel a station was on could differ widely between regions, so the channel number was just a local implementation detail. There is/was also usually some more or less common order of stations, e.g. in Germany you'd always put ARD on 1, ZDF on 2, the regional "third" station on 3...
- crymer11 7y agoIf anyone is interested in amateur radio in the US, don't let the current situation dissuade you. There is at least one VEC now offering completely remote exams - I just took both my Technician and General exams with GLAARG completely remote.
- jld 7y agoGiven there is a question in the Amateur Extra exam question pool about how VECs can properly conduct a remote exam, I'm surprised this isn't more widespread.
- nullc 7y agoAny idea if GLAARG is in need of more VEs to conduct remote tests? I'm an extra in the bay area and know a couple others who would be willing.
- crymer11 7y agoNo clue - I barely got the chance to speak with any of the VEs; I joined the call, showed them my testing environment, took the exams, then they quickly reviewed results and next steps before leaving to start the next candidate's process. They had a day full of reservations to take exams and a pretty large waitlist of people waiting to squeeze in when they had extra time.
- drmpeg 7y agoFM stations broadcasting HD Radio are 400 kHz wide. http://www.w6rz.net/fmbandzoom.png http://www.w6rz.net/fmbandzoom.png
- unixhero 7y agoNorway killed its FM transmission, a perfectly functioning technology. Pure one to many distribution perfected over time, deprecated. DAB+ radio has much lower range and the signal is unstable. To make matters maybe even worse, HAM radio operators at work inform me the DAB+ standard isn't going anywhere and that the development has mostly stopped. Maybe somehow 5G can do some marvels for the technology, time will tell.
- LeoPanthera 7y agoI'm normally pro-digital over anything analogue, but broadcast radio is one medium, possibly the only medium, where analogue is better. Digital compression simply doesn't cope with packet loss well enough to be practical. Even with a very weak FM signal, in emergencies you can still hear through the noise.
- RandomBacon 7y agoIn rural places in the US, it's terrible for television. Several years ago, it was mandated that TV stations switch from analogue to digital. Now instead of getting a little static and being able to understand 100% of what is said and shown over the air; it's now 10% recognizable video 90% visual blocks, and 0% audio.
- jdofaz 7y agoIf the digital transition hadn't happened I think over the air television might have died by now. Analog broadcast used significantly more electricity and fewer and fewer people would be interested in the low quality signal. Stations might have decided the remaining viewers weren't worth the power cost. That said I think streaming might kill it anyway.
- generatorguy 7y agoCan you quantify the difference in electricity costs? Start with difference in Watts, guess 0.15$/kWh and then find $/year saved? I bet the increase in quality and maybe the reliability or support costs for the old analog equipment were bigger factors.
- Venkatesh10 7y agoNot in India atleast, we have fm stations at 93.8, 106.4 and so on.
- jakub_g 7y agoSame in Poland. Example: https://www.rmf.fm/radio/ https://www.rmf.fm/radio/
- kiwijamo 7y agoSame as in New Zealand (NZ). Plenty of even frequencies here.
- reaperducer 7y agoIt haas nothing to do with quantity or scarcity of frequencies.
- reaperducer 7y agoSince the article is on a US government web site, it wouldn't have information about India.
- jeffdavis 7y agoThe article doesn't really answer why. It basically says that FM is channelized first and then the center frequencies are determined; while AM is assigned center frequencies first. But why are AM and FM different here?
- jedberg 7y agoWhen I was a kid we replaced our radio and got a fancy one that could go in .1 increments, which let us hit the even numbers. It was nice to be able to get far away stations by hitting the even numbers as long as there wasn’t a neighbor station.
- phire 7y agoI once had a car radio which enforced this rule. Wouldn't tune to anything except odd decimals. And it worked fine in my home city, every single radio station was on an odd frequency. But I don't live in the US. One day I went on holiday to another city, and in that city and 90% of radio stations were on even frequencies. The poor radio refused to tune into them. You could set it to the neighbouring frequency and get it half tuned in, but it would never lock.
- fortran77 7y agoNot in Europe.
- delecti 7y agoI suppose "frequency modulation" (FM) would mean that you'd need to separate frequencies so each station can "modulate" without running into the neighbors. That's quite a satisfying thing to learn.
- deepspace 7y agoWell, that is an intuitive way of looking at things, but ANY signal carrying information has non-zero bandwidth. Even an AM (amplitude modulation) signal occupies a band of frequencies.
- jhallenworld 7y agoWhy are the AM channels spaced 9 KHz in Europe? You need to be careful when you buy a low cost car radio due to this..