Why Do FM Frequencies End in an Odd Decimal? (2015)
fcc.gov
fcc.gov
(Looked up after many hours of road tripping through states with very few radio stations)
https://en.wikipedia.org/wiki/Non-commercial_educational_sta...
Where exactly the band is and its channel spacing generally differs a lot between countries.
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.
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.
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.
That said I think streaming might kill it anyway.
I bet the increase in quality and maybe the reliability or support costs for the old analog equipment were bigger factors.
But with a digital signal, as long as you can distinguish individual bits, the picture is always perfect, so you can get away with a much lower signal strength.
But radio is often received by moving receivers, for which there is no good solution, and analogue will always be better.
At least on FM, on AM it doesn't work well for me.
The worse part, to me, is that it takes quite a long time for the HD signal to lock in. I had a brand new rental car last month with a brand new HD radio in it. It took upwards of ten seconds for some of the HD signals to lock in.
Radio stations (AM and FM) can improve this by going all-digital, instead of the hybrid technology almost all are running right now. But doing so not only excludes hundreds of millions of older radios, it reduces the coverage area. It's simply not worth the revenue hit, since in radio coverage area is everything.
On the plus side, I had a great Sony HD tabletop radio that I loved dearly. It had an iPod dock on top and if a song came on the radio that you liked, you'd press a button and the track information would be stored in a special playlist the iPod.
Then the next time you plugged the iPod into iTunes, it would match the information from the playlist and you could buy the song you heard on the radio from iTunes. It worked really well. I wish something like that existed for satellite radio.
I've always wondered what full digital stations do, but for the reasons you've said I doubt there are any.
It's not digital compression that the important bit, but the error correcting code: https://en.wikipedia.org/wiki/Coding_theory
I mean, this is already how satellite (especially interplanetary satellite) communication works.
That makes the station both sound awful and be significantly less reliable for reception.
I have been trying to look up what this I-frame-less encoding method is called, but it's impossible to find niche topics like this on Google or DDG these days (tried intra sweep, iframeless, progressive intra, without iframes, etc).
A lucky few with cars old enough to have a standard DIN car stereo bracket simply popped out the FM radio and dropped in a DAB replacement.
But, essentially, radio listening in both car and home dropped off a cliff.
Edit: The Great FM Kill-Off was a double whammy as they simultaneously stopped broadcasting DAB using the MPEG2/L1 codex and switched to DAB+' HE-AAC.
This made sense, technologically - sound quality of low bitrate MPEG2 is not impressive - but the result was that most early adopters of DAB had to purchase new receivers yet again as early DAB sets did not support DAB+.
Further, leading up to the FM shutdown all the focus was on FM=>DAB, not DAB=>DAB+ - so during the switch, three of my four DAB radios went the way of the dodo bird without me even having realized it was going to happen. I wasn't very motivated to buy new receivers yet again...
My new car has DAB+ but it also has tunein and spotify built-in so that's a much better option.
FM isn't dead yet here in Norway though you can still listen to local stations via FM and it looks like the license for them will be extended to 2031.
https://en.wikipedia.org/wiki/Low-power_broadcasting#FM_radi...
AM had the nice property that it worked somewhat in mountainous areas, but it didn't sound very good. It had the nice property of range.
FM sounded better than AM but had to be more-or-less line-of-sight. It also had the nice property of range.
DAB+ is like an abandoned FOSS project that everyone jumped on like it was Zoom before naked dudes were jumping into online church services and online elementary school classes with zoombombing.
5G is boondoggle unrelated to radio for cellular connectivity that requires much more infrastructure since sub-mmw can't go through many materials at its higher frequencies. I swear it's a conspiracy (theory) to sell 50x more tower gear than 4G LTE. We already have gigabit 4G LTE, sub-mmw 5G just seems uneconomically undeployable at-scale.
Technologies shouldn't be adopted simply because they're new or being pushed by vendors. Heck, Apple doesn't even have any 5G phones because 5G may not survive once the major carriers wise-up.
I’m pretty sure the next generation of Apple phones (iPhone 12?) will be 5G compatible, when the current generation came out 5G was barely deployed (still isn’t in a lot of places). So that’s more a matter of timing than Apple not believing in the technology.
agree with your reasoning, not your conclusion.
I don't think there will be material 5G buildout by the end of 2020 (even before the Covid-19 crisis I didn't believe that). So unless there's an important market with significant 5G buildout (not sure anybody really has "significant" and certainly none of the important markets do) they'll continue to wait.
This is especially true as current 5G devices have larger physical size and abysmal battery life. Apple can't fix that problem on their own; part of the problem is build out and part of it will need to be solved through the experiences of the radio chip vendors and their current customers.
Compare this, say, to WiFi 6 which Apple already deploys in their 2019 iphone 11 and 2020 ipads. hat is a little ahead of the curve (chip sets are OK but there's little deployment yet). Wifi base station deployment will trickle out and until then there's no negative cost for Apple's users (i.e. no effect on battery nor size).
AM can sound better, but it requires people to buy new radios, and the whole point of AM is that it's cheap.
I had a Sony AM Stereo Walkman, and if the station was broadcasting in AM Stereo, the sound was considerably better. Not FM quality, but not too far off to my ears.
On the frequencies that 4G uses, 5G is a moderate upgrade. Somewhat better speed, notably better latency.
5G will also add more wifi-adjacent frequencies, only slightly higher than existing networks use, which sounds like a perfectly good idea to me in dense areas.
It also uses a bit less power at the transmitter, but the receivers are more complex and need more power than FM receivers (afaik), which is a bad tradeoff.
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.
I've never had anything lock up on those .05 frequencies though. I wonder if it's every used anywhere.
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.
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.
https://en.wikipedia.org/wiki/Channel_6_radio_stations_in_th...
But why are AM and FM different here?
Analog broadcast channels do have 6 or 8 though, https://en.wikipedia.org/wiki/Television_channel_frequencies...
Original NTSC monochrome television is a 6 MHz wide channel, the video carrier is 1.25 MHz up from the bottom, and at the transmitter a filter lops off most of the lower sideband.
For receivers, the problem is the IF filter. Filters with steep skirts are hard to build and align, and are expensive. So... channel allocation was done with the assumption that most consumers would have receiving sets with poor adjacent-channel rejection because of using cheap filters. This was solved by channel allocation -- do not let two stations with overlapping grade-A signal contours be on adjacent channels. Problem solved.
In the very early days in the US, channel 1 was 48-54 MHz. They found out that the percentage bandwidth was too wide to be able to build a practical transmitting antenna for channel 1. The SWR was too high at the band edges, and high SWR on analog TV means the transmission line generates ghost pictures. So channel 1 was dropped. Now hams have the 6 meter 50-54 MHz band, and cheap license-free R/C toys and walkie-talkies have 48-50 MHz.
Channel 2 is 54-60, 3: 60-66, 4: 66-72 and then a gap: 72-74 is radio control, then channel 5 is 74-80, and so forth, and if I recall correctly there is a big gap between channels 7 and 8 so even though they are sequential numbers they are not frequency-adjacent channels. (7 and below being the so-called "low VHF" and 8-13 the "high VHF" TV channels.)
The 2 MHz gap between channels 4 and 5 was also used to advantage, as it was enough to eliminate the adjacent-channel interference problem on reception. I recall when I lived in Minneapolis, that channels 2, 4, and 5 were all allocated in the metro area. Channel 3 was Mankato, far enough away that if you lived between Minneapolis and Mankato you could receive all of those stations without interference problems, being in the grade-B signal contour of both.
And..... this entire post contains obsolete information of historical interest only, and even at that, of interest to very few. Now... excuse me because I have to readjust the spark gap on my 200 meter transmitter...
https://www.ntia.doc.gov/files/ntia/publications/january_201...
Not terribly surprised though, Title 47 is crusty and full of surprises - these channel numbers are certainly defined somewhere.
You can see why I say Title 47 is crusty.
Then the station you work for must not have any repeaters or translators.
When you hear a legal ID like "KHNH/Randoville, K226AR/Hacktown," the translator it got its call sign because it's on channel 226. All of the AM frequencies have channel numbers, too.
I worked in radio for ten years, and wasn't even on the technical side, and I knew this.
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.
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.
I think the FM callsigns for the same station were different (four characters rather than three), however could be related, but the callsigns were eventually dropped or incorporated into the station name as it stopped being a thing broadcast stations needed to announce (or maybe even have.) For example, as the station that had that antenna above started FM, it had a callsign but now it's just left in the name: https://en.wikipedia.org/wiki/ZM_Wellington
Same on TV, when I was a kid our PBS stations always went by KAET, later on they went by the channel number Eight. Now that people might not even be watching on a channel (streaming) they just go by Arizona PBS, but every once in a while they show their station callsign and the call sign of all the translators (stations that transmit identical signal in other parts of the state)
They're used everywhere, but not every country requires them to be spoken aloud. They can be transmitted or recorded in other methods that are not audible to the listener.
Japan, for example, uses the American method. You can hear it if you stream JODW/Tokyo.
Translators can have even more characters and are a combination of numbers and letters.
Experimental stations are generally W or K a region digit, and three letters starting with X, these are issued out of the pool of callsigns used for amateur radio stations.
Buiness band and GMRS licenses use the same format, generally three or three letters starting with K or W, and three or four numbers.
See for more information: https://www.ecfr.gov/cgi-bin/text-idx?&mc=true&node=sp47.1.2...
All commercial radio and television stations in the US have call signs starting with K or W. The division is geographic -- west coast stations use K; east coast stations use W. (The dividing line is, roughly speaking, drawn at the Mississippi River.)