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Why Do FM Frequencies End in an Odd Decimal?

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Re: Why Do FM Frequencies End in an Odd Decimal?

#11

Post by smoyer »

Yep ... 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#Vest...

Re: Why Do FM Frequencies End in an Odd Decimal?

#12

Post by gorner »

kps wrote: post #7

Wikipedia¹ 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 s…

In 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.

Re: Why Do FM Frequencies End in an Odd Decimal?

#13

Post by TallGuyShort »

bnegreve wrote: post #9
datawander wrote: post #4

Earlier quoted context omitted.

Yes, 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/Freq…

> [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?

As 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.

Re: Why Do FM Frequencies End in an Odd Decimal?

#14

Post by talmand »

miahi wrote: post #3

This 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.

I 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.

Re: Why Do FM Frequencies End in an Odd Decimal?

#15

Post by ds9 »

datawander wrote: post #4
blueblob wrote: post #2

Did I miss something, or did this not answer the question in it's heading? It basically says it's like this in the US.

Yes, 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/Freq…

Another 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

Re: Why Do FM Frequencies End in an Odd Decimal?

#16

Post by qbrass »

bnegreve wrote: post #9
datawander wrote: post #4

Earlier quoted context omitted.

Yes, 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/Freq…

> [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?

>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.

Re: Why Do FM Frequencies End in an Odd Decimal?

#18

Post by jejones3141 »

ef47d35620c1 wrote: post #10
kps wrote: post #7

Wikipedia¹ 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 s…

RCA 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 mod…

I'd be among them, since he also came up with the regenerative, superregenerative, and superheterodyne radios.

Re: Why Do FM Frequencies End in an Odd Decimal?

#19

Post by steeve »

miahi wrote: post #3

This 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.

The first and only time I saw a radio with odd only decimal frequencies was in the US. Nowhere else.

Re: Why Do FM Frequencies End in an Odd Decimal?

#20

Post by amalag »

ds9 wrote: post #15
datawander wrote: post #4

Earlier quoted context omitted.

Yes, 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/Freq…

Another 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

It 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.
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