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Why Do FM Frequencies End in an Odd Decimal?
- nathan_f77 13y agoAuckland, New Zealand seems to have mostly "even decimal" FM stations. 95.0, 90.2, 99.8, to list a few.
- dfc 13y agoPSA: If you 404 turn of httpseverywhere for fcc.gov.
- blueblob 13y agoDid I miss something, or did this not answer the question in it's heading? It basically says it's like this in the US.
- datawander 13y agoYes, that's exactly why, because the FCC said to do it that way. There are countless examples of "why is it this way" being answered "because that is what some arbitrary person picked." My favorite example of this I remember reading in Andrew Tanenbaum's Networking book that the first frequency-hopping protocols used 88 frequencies because that is how many keys there are on a piano: https://en.wikipedia.org/wiki/Frequency-hopping_spread_spectrum#Multiple_inventors https://en.wikipedia.org/wiki/Frequency-hopping_spread_spect...
- kkjkok 13y agoThe most interesting part of that is the WHO of spread spectrum... Hedy Lamarr (movie star) and George Antheil (composer). Very fascinating that two major Hollywood players were able to innovate in hard science/math. A different era. I think the piano keys stuff was because the idea was semi-based around a player's piano (if I recall the legend from my DSP prof). The roll moves around and different bumps make the notes sound - a similar concept (visually at least) to coding a communications signal and having it jump all over frequency. 88 notes -> 88 frequencies. I wouldn't be surprised if the experimental equipment was a modified version of a player's piano. Very cool stuff, though I may be recollecting the story wrong. Wikipedia agrees about the movie star + composer bit at least.
- baddox 13y agoArticle with headlines like "Why X was chosen" are expected to actually provide explanations of human motivation, rather than the nearest proximate cause. For example, an article called "Why this stretch of highway has a speed limit of 30 mph" would be expected to say something like "because there is a history of accidents there due to the narrow shoulder and tight turns" rather than "because the transportation department, which is in charge of setting speed limits, posted 30 mph signs there."
- bnegreve 13y ago> [Why] the first frequency-hopping protocols used 88 frequencies because that is how many keys there are on a piano Well, it is a rather arbitrary reason but a valid explanation. In the case of FM frequencies, the question remains ... why did they picked odd frequencies?
- coin 13y agoThe frequency is the center of a 200kHz channel. The first channel is 88.0 - 88.2 MHz, thus the center is 88.1.
- TallGuyShort 13y agoAs they say, "The center frequency is located at 1/2 the bandwidth of the FM Channel, or 100 kHz (0.1 MHz) up from the lower end of the channel." It's natural to pick a range between round numbers. so 88.0 MHz - 108.0 MHz doesn't seem so strange a range to be allocated. Now if one band starts at 88.0 MHz and needs 200 kHz of bandwidth, it's going to go from 88.0 MHz to 88.2 MHz. The carrier frequency will be in the middle of this band, so it's represented as 88.1 MHz.
- qbrass 13y ago>Well, it is a rather arbitrary reason but a valid explanation. It's not exactly arbitrary, it was inspired by a player piano, and the original patent used piano rolls. Using all of the keys just makes sense in that context.
- ds9 13y agoAnother example is the Fahrenheit scale. The eponymous originator calibrated his thermometer by the temperatures where he could obtain brine (0 F) and an inaccurate estimate of human body temperature (100 F). https://en.wikipedia.org/wiki/Fahrenheit https://en.wikipedia.org/wiki/Fahrenheit
- amalag 13y agoIt is still nice because it is human centric, roughly 0 to 100 for temperatures is easily relatable to the human body. 90 is hot, 10 is cold. Celsius starting at the freezing point of water is not as human centric.
- raverbashing 13y agoNo, it's still a piece of crap "Human centric" is a false advantage. And it's not even human centric, the temperature of 100F is wrong, and what does brine have to do again with the human body?
- fancyketchup 13y agoGah. Can we please stop with this bullshit already? Fahrenheit has nothing to do with body temperature. The human body temperature is ~100F by coincidence, not by design. The Fahrenheit scale has 180 divisions (nice round number, evenly divisible by loads of integers) between the freezing point of water and the boiling point of water (212F-32F=180, for the math challenged). The 0F point is the equilibrium point of a frigorific mixture of equal parts ammonium chloride, ice, and water. One can easily produce two reference points for the F scale in a way that isn't sensitive to the local pressure using just ice brine (0F) and ice water (32F). The melting temperature of ice and the equilibrium temperature of the brine mixture are constant on the pressure scales and temperature scales available to metrologists before about the 19th century[1][2]. The same can't be said for the Celsius scale, which requires either a triple-point cell or a known atmospheric pressure (so that the boiling temperature of water is well-known). Edit: So the close out the point, the Fahrenheit is a unit which is much better matched for the calibration tools and computational methods available around the time it was invented. [1] Maybe a better way to state this sentence is that the temperatures are constant "to within the experimental uncertainty achievable at the time." [2] It's well known to anyone who has ever cooked that water boils at an appreciably different temperature in Denver than in Los Angeles.
- pwg 13y agoIt's the typical "write a lot, but don't really answer anything" style that so many politicians utilize, only substituting "talk" for "write". The entire section could have been summed up as: Because each broadcast band is identified by the frequency of the center of the band, the bands begin on an even number, and the bands are two "units" wide, making the center frequency an odd number. Edit: for clarification.
- dfc 13y agoThe text was most likely written by a civil service employee. Civil servants are not politicians.
- GauntletWizard 13y agoYou've clearly never worked in Civil Service.
- dmur 13y agoI don't think pwg was implying civil servants are politicians, rather merely pointing out that the text reads like a political speech.
- pwg 13y agoCorrect conclusion.
- miahi 13y agoThis only happens in the US, probably. The fun fact is that some car manufacturers believe this is global, so they only allow odd frequencies on the car radio.
- nkvoll 13y agoWe had a radio in our old Chrysler Voyager that required a pretty insane secret code being entered (turning it off and on again 5 times in a row or something like that was part of it) in order to enable to tune to regular EU frequencies...
- richardw 13y agoMy 2013 VW Golf has a similarly mad method to move the windscreen wipers to a position that enables the window to be cleaned. I forget the trick - I think its turn the car off, then on, then move the wiper stalk to one of its four or five positions. Or vice versa. I really can't remember. Edit: switch ignition on, then off. Briefly press the down the windscreen wiper lever.
- laacz 13y agoOh, that servicing position. That's because you can't lift wipers from their resting position since bommet is too close to windscreen. You have to turn on the ingition, turn it off and then hold wiper stalk in the lowest position for 2 seconds. Same goes for 2013 Skoda Octavia. Had to learn that yesterday :)
- talmand 13y agoI recently watched an episode of Top Gear where Clarkson was driving a Ford Mustang and used the odd-number ending frequencies on the radio as a part of his never-ending "American cars are weird" joke.
- steeve 13y agoThe first and only time I saw a radio with odd only decimal frequencies was in the US. Nowhere else.
- kps 13y agoWikipedia¹ has a more interesting answer to "Why?" — After World War II, the FCC moved FM to the frequencies between 88 and 108 MHz on June 27, 1945. The change in frequency was said to be for avoiding possible interference problems between stations in nearby cities and to make "room" for more FM radio channels. However, the FCC was influenced by RCA chairman David Sarnoff, who had the covert goal of disrupting the successful FM network that Edwin Armstrong had established on the old band. ¹http://en.wikipedia.org/wiki/FM_broadcasting_in_the_United_States#History_of_FM_radio_in_the_U.S http://en.wikipedia.org/wiki/FM_broadcasting_in_the_United_S....
- ef47d35620c1 13y agoRCA went after Armstrong. They knew that by convincing the FCC to change the frequencies they could seriously disrupt FM and make existing equipment useless. Armstrong later committed suicide. His wife won all of the on-going lawsuits. Basically, RCA broke him financially and mentally with multiple lawsuits and years of "discovery". Armstrong is the father of frequency modulation (FM) and some argue the father of modern radio.
- twoodfin 13y agoKen Burns did a terrific documentary on the RCA/Armstrong fight and the birth of radio generally, Empire of the Air. http://www.pbs.org/kenburns/empire/ http://www.pbs.org/kenburns/empire/
- jejones3141 13y agoI'd be among them, since he also came up with the regenerative, superregenerative, and superheterodyne radios.
- gorner 13y agoIn fairness that's more about the current range of FM frequencies (originally in the 42–50 MHz range), not why they all end in an odd number.
- icodestuff 13y agoI had an Aiwa stereo/receiver several years ago that could tune the FM radio in 50kHz increments instead of 200kHz. Most stations were weaker 50kHz off, but a few were stronger. More interestingly, there were one or two stations I could only get on the even decimals, usually between two empty odds. Now I wonder if someone's transmitter was configured incorrectly, or whether it was an illegal broadcast.
- smoyer 13y agoYep ... the (unmodulated) carrier frequency is in the middle of the channel (as it is with most AM radio stations). What's more interesting is to look at the old analog television broadcast channels. They were transmitted using VSB AM (Vestigal Side-Band Amplitude Modulation) which effectively meant that the luminance information (brightness) was transmitted using both side-bands (regular AM) but the chrominance information (color) was transmitted using SSB (Single Side-Band). http://en.wikipedia.org/wiki/Single-sideband_modulation#Vestigial_sideband_.28VSB.29 http://en.wikipedia.org/wiki/Single-sideband_modulation#Vest...
- zwieback 13y agoNever noticed that it's like that here in the US. My radio station growing up was SDR3 on 92.2 and channels are spaced .1MHz apart -- apparently the channel assignment in Germany took a different path.
- __david__ 13y agoWhat actually more interesting to me is that FM has assigned channel numbers. I don't think I've ever seen a consumer radio that used channels instead of the raw frequency. I never knew they existed until I read that.
- lutorm 13y agoThey mean "Why do U.S. assigned radio-station FM frequencies end in an odd decimal"...
- deleted 13y ago[deleted]
- mayonnaise23 13y agoI imported a car from Japan and it would get audio from TV stations as the radio went down to lower frequencies =)
- aestra 13y agoBefore the North American conversion to a digital only TV broadcasts, the audio for all analog channel 6 television stations in the United States could be picked up on 87.7 FM Some channel 6 stations have expressed interest in/have implemented also broadcasting the sound for their broadcasts back on radio again after moving solely to digital broadcasts. http://en.wikipedia.org/wiki/87.7_FM http://en.wikipedia.org/wiki/87.7_FM