Why Do FM Frequencies End in an Odd Decimal?(transition.fcc.gov) |
Why Do FM Frequencies End in an Odd Decimal?(transition.fcc.gov) |
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.
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.
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_spect...
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.
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?
Edit: switch ignition on, then off. Briefly press the down the windscreen wiper lever.
http://en.wikipedia.org/wiki/Single-sideband_modulation#Vest...
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.
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.
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.
"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?
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.
Whereas “reasonable” temperatures in C run from what, -18ish to 38ish? Where’s the sense in that?
If you want to defend a unit of temperature, defend Kelvin. Don’t pretend that ˚C is significantly more reasonable than ˚F. They’re both bonkers in their own way (mysticism about the vitality of water is not a real justification).
If (more likely) you just want to make fun of Americans for being rubes, use distances or weights or volumes as your example.
My bigger question is why Metric stuck with Celcius and Kelvin instead of factoring in the Gas Constant (R) into Kelvin so the math would be completely constant-free.
Of course, then you'd have water freezing at 2271 and boiling at 3102, which wouldn't be fun in conversation.
That's a really good question. Another possibility would be to fix the calories/joules mismatch in heating water
Celsius is easy, 100. :)
Choosing the freezing point of water isn't really mystic. It lets you know whether it will rain or snow. It also means that any negative temperature is capable of causing frostbite.
Not really, since it depends upon temperature at the clouds, not at the ground level. Oh, and it also depends on atmosphere pressure, and on time (since a phase change requires latent heat transfer in addition to merely being at the right temperature).
And as baddox mentions, 32 is hardly harder to memorize than 0, especially if you know anything at all about computers.
Fahrenheit also has a chosen freezing point of water: 32 degrees. This is no more difficult to remember than Celsius' zero degree freezing point.
Sure, at 100, healthy humans can survive as long as their increased water needs are met. (Sun is another matter, but I'm just talking temperature.)
However, at 0F, permanent tissue damage onset is within 30 minutes, with almost any wind speed. (http://www.nws.noaa.gov/os/windchill/images/windchillchart3....)
I'm not disputing the 0F to 100F (or -18C to 40C) range in terms of being "regularly seen".
EDIT: I suppose the core of the misunderstanding is that I was addressing the "human centric" advantage and relation to brine, where you were just arguing (quite reasonably) the convenient representation of the range?
However, I'd argue that being water-based is hardly mystical: if water is boiling, or frozen, survival is more difficult. It's also a pragmatic system for any nation that regularly drops below freezing. (Eg, could it snow today? Could there be ice to slide on?)
Water was also used in the original definition of a gram, which is a fairly good reason to reuse it in another definition.
To your edit: yes, I think that’s the real thing. I certainly don’t think the brine thing is reasonable, just that 0-100F is a nice range.