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why the radio based on frequency modulation has very small transmission area?
Could we please stop moving the disambiguation page and setting to FM. FM does stand for more than one thing. Thank you. --Numerousfalx 23:51, 15 Dec 2004 (UTC)
Can someone give an example for frequency modulation? let's say there is a test signal low tone, high tone, and a sweep. this composed audio signal is supposed to be put on FM radio - how would the modulated tone look like? how much bandwidth does FM radio need? When I detune my favorite radio station "92.2 MHz Rock" by, let's say +0.2 MHz, will the music and all transmitted acoustics be pitched to higher frequencies (so that radio moderators talk like Mickey Mouse) - or is FM resistant against those mistunings.
It would be great if someone could work my (answered) questions into the article. Thanks, --Abdull 21:41, 17 Jan 2005 (UTC)
The article reads as "FM as used in radio" with a little theory thrown in at the last minute. Shouldn't an article titled "Frequency Modulation" primarily cover the theory and link to separate articles on radio/data transmission/encoding (and FM synthesis)? The FM synth article has almost no theory at all.
That might be because the authors of the FM Synth article are unaware of that FM-synthesis á la Yamaha is based on phase-modulation. /ja
The first sentence "...represents information as variations in the instantaneous frequency of a carrier wave" makes sense if you're reading about radio, but is hard to "get" if you're coming at this from the FM synth perspective.
Please have a look at the discussion page under "phase modulation" where I present a few C like oneliners to make the point. /ja
I suppose it makes sense to add a bit more on the theory, whether the article should have its current focus or not; I'd do it myself, except for the fact that I don't really understand FM all that well yet.
magetoo 14:16, 27 Apr 2005 (UTC)
But why not add a see also in both articles
Theking2 (talk) 16:52, 27 November 2023 (UTC)
"The phrase frequency-modulated, an adjective, should have a hyphen when used attributively."
Could the author consider changing the font on the maths? I found it very difficult to see on a computer screen whether I was reading "t" for time or "f" for frequency. Otherwise found the article well balanced.
The main theory discussion has a very common mistake in deriving frequency modulation. I picked up on it because I make the same mistake every time I start to review FM, and have to fix it. The formula x(t) = A*cos(2*pi*f(t)*t) is incorrect. It arises because A*cos(2*pi*f*t) is correct when f is a constant - f is the frequency. However, frequency is the rate of change of the cos() argument. If f(t) is time varying, then the rate of change of f(t)*t is not f(t), it is some complex derivative that is no fun at all.
A better derivation is to start with x(t) = A*cos(phi(t)). Frequency is defined as the rate of change of phi(t). To get sinusoidal FM, we need some phi(t) such that the derivative of phi(t) is 2*pi*deviation*cos(2*pi*rate*t). That isn't so hard - we know the derivative of sin(kt) is k*cos(kt), so we postulate phi(t) = deviation/rate *sin(2*pi*rate*t). It is inconvenient to carry the ratio of deviation/rate, so it is often called Beta. The final formula, then, is x(t)=A*cos(Beta * sin(2*pi*rate*t)) where Beta is deviation/rate, and both deviation and rate are in Hz.
This leads nicely to the Bessel functions, which are a formalized way of working out equations like cos(m sin(x)).
References: "Analog and Digital Communications" by Hwei Hsu (Schaum's Outline) and "Fundamentals of Electronics" by Aldo Vieira da Rosa. (above written by Doug olney)
"FM is also used at intermediate frequencies by most analog VCR systems, including VHS, to record the luminance (black and white) portion of the video signal."
Has this method ever been tried for audio recording, aside from the HiFi modes on some analog VCR systems such as VHS and Betamax?144.139.87.8
FM of an audio-frequency carrier has been useful as a means of recording low-rate digital data on audio tape (cassette) recorders. Such audio equipment could not handle long strings of repeated 0's or 1's directly because of limited low-frequency response.Cuddlyable3 19:01, 12 February 2007 (UTC)
"FM is the only feasible method of recording video to and retrieving video from magnetic tape without extreme distortion, as video signals have a very large range of frequency components — from a few hertz to several megahertz, too wide for equalisers to work with due to electronic noise below -60 dB. This sentence tries to say too many things and needs attention. The megahertz-wide frequency range of video does not force any particular choice of modulation method, nor is it difficult to "equalise" over the video frequency range. I think the subject of FM in video recording belongs in a new section, where the significant issues treated are linearity, pre- and post-emphasis, tape speed, head gaps and noise distribution.Cuddlyable3 18:53, 9 February 2007 (UTC)
The statement of "Commonly, the chrominance component is recorded as a conventional AM signal, using the higher-frequency FM signal as bias." of appears to be referring to the VHS system and this isn't true. The chrominance signal is recorded using the "color under" system. The 3.58 MHz subcarrier is simply downconverted to a lower frequency and recorded along with the luminance signal. Maybe this whole section should be scrapped and links given to FM video recording systems such as VHS and data recording such as the Kansas City Standard. (Even though the latter is rarely used these days.) — Preceding unsigned comment added by 96.240.175.232 (talk) 01:31, 20 December 2013 (UTC)
The animation is nice. However the AM example is jerky, gives an impression that carrier cycles are individually modulated, and they don't look sinusoidal. There is also redundant text "modulatie", not even in English (the M's stand for modulation already). I think we have to look extra critically at animated drawings because of the relatively high data overhead they represent.Cuddlyable3 15:19, 15 February 2007 (UTC)
I have fixed the above with a new animation. Besides being accurate and non-language specific, it is a much smaller file, and we all like pages to load quickly, don't we?Cuddlyable3 01:04, 18 February 2007 (UTC)
I may be wrong, since I'm still studying elementary physics, but does the first graph show a frequency over time (signal) superimposed on an amplitude over time (carrier)? To remain consistent, I would think that the two graphs should have the same two variables. --Pyg 01:09, 11 March 2006 (UTC)
I think the first image (AM, green waveform) is incorrect - it should be showing a varying signal amplitude (vertical scale) at a fixed frequency. Nogami 00:47, 12 August 2006 (UTC)
There seems to be something wrong with the formula. It is different from the one shown in one of the external links (http://www.fas.org/man/dod-101/navy/docs/es310/FM.htm). In this page the formula does not involve an integral at all. It seems to me that the formula as it is now requires the time integral of the signal Xm(t) from 0 to t to be restricted to [-1,1] for all t. This is not necessarily true even if |Xm(t)| < 1. Also it would be interesting to know how to recover the transmitted signal from the modulated carrier wave.
Could someone expand the theory section significantly? I think it could use more math/physics background and a sub-section on the engineering of actually accomplishing frequency modulation. Ryanluck 15:55, 6 November 2006 (UTC)
I disagree that the theory section needs more math/physics background. FM and radio is essentially the product of engineering and the mathematics behind it is nice to understand - but not fundamental. The explanation of FM given here is equivalent to asking someone the time and getting and answer on how his watch was built with a precise explanation of the location of every cog in the structure. It may in fact include the information being sought, however more than likely the questioner still won't know what time it is. A far more practical explanation of the theory of frequency modulation is given in the reference http://www.fas.org/man/dod-101/navy/docs/es310/FM.htm:
Frequency modulation uses the information signal, Vm(t) to vary the carrier frequency within some small range about its original value. Here are the three signals in mathematical form:
* Information: Vm(t) * Carrier: Vc(t) = Vco sin ( 2 p fc t + f ) * FM: VFM (t) = Vco sin (2 p [fc + (Df/Vmo) Vm (t) ] t + f)
Df is the peak frequency deviation. In this form, you should be able to see that the carrier frequency term: fc + (Df/Vmo) Vm (t) now varies between the extremes of fc - Df and fc + Df. The interpretation of Df becomes clear: it is the farthest away from the original frequency that the FM signal can be. Sometimes it is referred to as the "swing" in the frequency.
We can also define a modulation index for FM, analogous to AM:
b = Df/fm , where fm is the maximum modulating frequency used.
The simplest interpretation of the modulation index, b, is as a measure of the peak frequency deviation, Df. In other words, b represents a way to express the peak deviation frequency as a multiple of the maximum modulating frequency, fm, i.e. Df = b fm.
Example: suppose in FM radio that the audio signal to be transmitted ranges from 20 to 15,000 Hz (it does). If the FM system used a maximum modulating index, b, of 5.0, then the frequency would "swing" by a maximum of 5 x 15 kHz = 75 kHz above and below the carrier frequency.
Here is a simple FM signal:
Here, the carrier is at 30 Hz, and the modulating frequency is 5 Hz. The modulation index is about 3, making the peak frequency deviation about 15 Hz. That means the frequency will vary somewhere between 15 and 45 Hz. How fast the cycle is completed is a function of the modulating frequency. —Preceding unsigned comment added by 67.142.130.42 (talk) 18:26, 5 October 2007 (UTC)
There is no explanation given of how the transmitted signal is recovered. That is cheating the reader after promising "The rest of this article...concentrates on the FM modulation [sic] and demodulation process." A solution could be instead to link to descriptions of the established FM detectors (Ratio, Foster-Seeley, Slope and PLL) in the article on Detector (radio).Cuddlyable3 17:54, 9 February 2007 (UTC)
The above is not true if by "common" we understand the majority of domestic radios.Cuddlyable3 19:06, 12 February 2007 (UTC)
The most common method used in commercial FM broadcast band radio receivers is the quadrature detector. See LM3189 datasheet for an IC that used to be the workhorse of FM detectors. Motorola AN189 gives some theory on how a quadrature detector works. The Foster-Seeley detector was common before ICs became common. — Preceding unsigned comment added by 96.240.175.232 (talk) 01:24, 20 December 2013 (UTC)
Could this article include the assigned frequencies for the different uses? Such as 118.00 – 136.975 for Aviation, 108.000-117.975 Navigation, 151.5125- 158.400 BRS. I think a side bar would be best served for this purpose. —The preceding unsigned comment was added by 70.41.64.103 (talk) 00:50, 15 February 2007 (UTC).
Specifically,
makes it difficult to understand the underlying circuitry.
There's no electronic circuit that can indefinitely accumulate a non-zero average input as implied by this equation; while the equation may or may not be correct, it will inevitably be an indirect parallel to the physical model. Also, is not clearly defined; the reader must infer it's nature from the integral, which may be incorrect.
would be a simpler, more direct mathematical model. It has a constant amplitude with a varying frequency.
is a possible scenario;
however, the article does not state (though it implies) that this the actual modulation.
The set of possible modulations is covered by where is flat long-term.
note: I don't know how to get a proper multiplication dot; hence my multiplication looks like a cross-product; feel free to fix that if you know how.
It would be more helpful to state the exact modulation, or the exact circuit.
—Preceding unsigned comment added by 66.245.28.149 (talk • contribs) 09:06, 4 July 2007
Thank you for your help; I found one of the external links (www.fas.org) presented FM in a set of equations that cleared everything up for me personally. The confusion in the Wikipedia article is the result of the definition for as "instantaneous maximum deviation": it's actually just a constant, but 'instantaneous implies that it is a variable in time.
After Carson's rule, Bessel Functions and their role in calculating aspects of the sidebands created by FM needs to be added. I have added it, but it needs more explanation, and the table title needs repair as below.
Modulation Index | Carrier | Sideband Pairs |
---|
1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | ||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
0.00 | 1.00 | ||||||||||||||||
0.25 | 0.98 | 0.12 | |||||||||||||||
0.5 | 0.94 | 0.24 | 0.03 | ||||||||||||||
1.0 | 0.77 | 0.44 | 0.11 | 0.02 | |||||||||||||
1.5 | 0.51 | 0.56 | 0.23 | 0.06 | 0.01 | ||||||||||||
2.0 | 0.22 | 0.58 | 0.35 | 0.13 | 0.03 | ||||||||||||
2.41 | 0 | 0.52 | 0.43 | 0.20 | 0.06 | 0.02 | |||||||||||
2.5 | −.05 | 0.50 | 0.45 | 0.22 | 0.07 | 0.02 | 0.01 | ||||||||||
3.0 | −.26 | 0.34 | 0.49 | 0.31 | 0.13 | 0.04 | 0.01 | ||||||||||
4.0 | −.40 | −.07 | 0.36 | 0.43 | 0.28 | 0.13 | 0.05 | 0.02 | |||||||||
5.0 | −.18 | −.33 | 0.05 | 0.36 | 0.39 | 0.26 | 0.13 | 0.05 | 0.02 | ||||||||
5.53 | 0 | −.34 | −.13 | 0.25 | 0.40 | 0.32 | 0.19 | 0.09 | 0.03 | 0.01 | |||||||
6.0 | 0.15 | −.28 | −.24 | 0.11 | 0.36 | 0.36 | 0.25 | 0.13 | 0.06 | 0.02 | |||||||
7.0 | 0.30 | 0.00 | −.30 | −.17 | 0.16 | 0.35 | 0.34 | 0.23 | 0.13 | 0.06 | 0.02 | ||||||
8.0 | 0.17 | 0.23 | −.11 | −.29 | −.10 | 0.19 | 0.34 | 0.32 | 0.22 | 0.13 | 0.06 | 0.03 | |||||
8.65 | 0 | 0.27 | 0.06 | −.24 | −.23 | 0.03 | 0.26 | 0.34 | 0.28 | 0.18 | 0.10 | 0.05 | 0.02 | ||||
9.0 | −.09 | 0.25 | 0.14 | −.18 | −.27 | −.06 | 0.20 | 0.33 | 0.31 | 0.21 | 0.12 | 0.06 | 0.03 | 0.01 | |||
10.0 | −.25 | 0.04 | 0.25 | 0.06 | −.22 | −.23 | −.01 | 0.22 | 0.32 | 0.29 | 0.21 | 0.12 | 0.06 | 0.03 | 0.01 | ||
12.0 | 0.05 | −.22 | −.08 | 0.20 | 0.18 | −.07 | −.24 | −.17 | 0.05 | 0.23 | 0.30 | 0.27 | 0.20 | 0.12 | 0.07 | 0.03 | 0.01 |
Phillipbeynon 04:24, 1 August 2007 (UTC)
I think this table is valid only when the modulating signal is a sinusoid - isn't it so? This should be mentioned. If the table has some meaning for non-sinusoidal modulating signals (as some kind of rule of thumb) it should be explicitly said. Matteosistisette (talk) 13:31, 17 February 2010 (UTC)
Why is it that most sources claim that an FM receiver only demodulates the strongest signal available, and yet one will sometimes hear two stations simultaneously? Does this indicate something is wrong with the receiver or is this 'normal' if the signals' strengths are the same order of magnitude? I have a few times been able to enjoy a talk and music at the same time using my car radio (KXBL 99.5 FM and KAKS 99.5 FM).
-User: Nightvid
FM and PM are really the same thing, separated only by the mathematical viewpoint. Perhaps they should be merged into one article and then have FM treated as a special case? HatlessAtless (talk) 21:48, 23 April 2008 (UTC)
Serrano24 (talk) 15:37, 20 June 2008 (UTC)
There should be a more intuitive way to explain these phenomenon. The derivations of the SNR's are horribly complicated. Does anyone have an easy way to explain this? Maybe we can even have a whole section on calculating SNR? —Preceding unsigned comment added by Daviddoria (talk • contribs) 22:14, 15 September 2008 (UTC)
This page has attracted several versions of animated diagrams that all attempt to illustrate the same thing. Animation "C" (see right) has recently been inserted without explanation for the change. We should now compare the available diagrams and gain a consensus on which one to use. (Please see some earlier discussion above.) Below is my assessment.
What do other editors think?—Preceding unsigned comment added by Cuddlyable3 (talk • contribs)
Specifically, the diagram FM Message and Modulated Signals.svg.
Which I clicked on the diagram, it says that f_delta = 0.15. I tried my best to work out and plot the equation of the green curve on my computer, but somehow it didn't work out. On closer examination, if f_c is 3 as stated on the file page, then f_delta of 0.15 seems too small for its effect to be noticeable on the graph. Are we sure f_delta is 0.15?
Also, I tried using other values of f_delta like 0.5, 1.5 etc and I couldn't get the green curve on the diagram.
Now let's say I simply made a mistake somewhere in my workings and that's why I have been unable to get the green curve, but there's something I've seen that doesn't seem quite right about the curve. If we examine equation (1) as referred to in the article, y(t) = A_c*cos(2*pi*f_c*t + 2*pi*f_delta*∫x_m(τ)dτ, the integral ∫x_m(τ)dτ represents the signed area of the region bounded within the data signal curve. Now, let's assume that this area between τ=0 and τ=t is represented by an average value of x_m_ave(t), so that ∫x_m(τ)dτ between τ=0 and τ=t equals x_m_ave(t)*t. Going back to Equation (1), it can be rewritten as
y(t) = A_c*cos[2*pi*(f_c + x_m_ave(t)*f_delta)*t]
What the above equation shows is that at time t, the instantaneous deviation between the frequency of the transmitted signal and f_c is dependent on the instantaneous amplitude of the data signal (i.e. x_m(t)). That is, at time t, the larger the value of x_m(t), the higher the instantaneous frequency of the transmitted signal; the smaller the value of x_m(t), the smaller the frequency.
After having said all that, if we look back at the green curve in question, it is at odd with the above conclusion. Can someone please comment on this? 222.152.22.151 (talk) 14:34, 13 April 2010 (UTC)
FM is currently a redirect to this article. That said, an non-exhaustive survey suggests that majority of incoming links are really referring to (the related) FM broadcasting article.
In this context, User:Georgia guy and I have been having a conversation over at Talk:FM about where the FM redirect should point.
If folks have a moment to read the conversation so far, we'd love some additional thoughts from other involved Wikipedians. Thanks in advance! —mako๛ 05:44, 27 September 2011 (UTC)
"The rest of this article concentrates on the FM modulation and demodulation process, which is identical in stereo and monaural processes." – No, it doesn't. Does anyone know where this sentence is supposed to go; it is now almost at the end of the article... -- megA (talk) 21:55, 6 November 2011 (UTC)
This article says "In analog applications, the difference between the instantaneous and the base frequency of the carrier is not directly proportional to the instantaneous value of the input-signal amplitude but it is proportional to frequency." where as article on FM Broadcasting says "In analog applications, the instantaneous frequency of the carrier is directly proportional to the instantaneous value of the input signal. This form of modulation is commonly used in the FM broadcast band." They are contradicting. Which is right? wikieinstein (talk) 13:03, 17 January 2013 (UTC)
This talk page is not a forum for general discussion or advice. Binksternet (talk) 15:14, 3 February 2013 (UTC) |
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The following discussion has been closed. Please do not modify it. |
Hello, could anyone explain, what about non-sinusoidal (and maybe non-periodic) carrier? Could we assume some FM( A(t), B(t) ) function, which modulates carrier, given by abstract function A(t) with signal, given by abstract function B(t)? could anyone write/explain something about that? what will formula look like in that most common case? I want some kind of recursive formula in terms, like "A(t-1)". Or either some explanation, if that is not possible and why. I was not able to find any info related to my question on the internet, so im here, asking people...— Preceding unsigned comment added by 95.143.213.249 (talk • contribs)
"rate modulation" is unsuitable, because i have no "future". I mean, i am not playing wav file, and i cannot just speed up it's playback. In other words, i'd say, i want to make "pitch modulation without rate increase" I am trying to code such dsp algorithm. It's heart is some discrete so-called "now" moment - you only have At and Bt sample, you must return Result sample value. Okay, you may have "past" if you want. You may succesfully obtain its previously stored "prev" values Aprev=A(t-1), Bprev=B(t-1), required for example in simple lowpass/hipass. You may store whole array and make delay line easily. You have "past", but you have no "future", which can become ONLY after calculation. And that's the task - to calculate the out result. What should we do, to "pitch-modulate" signal A(t) with B(t) in such enviroment& Where B(t) / B(t-1) == 2 means that A's pitch must be increased twice, resulting in 2 times higher percepted tone, but without "speeding up" playback. — Preceding unsigned comment added by 95.143.213.249 (talk) 14:38, 3 February 2013 (UTC) |
The article claims that Armstrong invented wideband FM. I'm not sure why "wideband". His early patents mention a modulation index somewhat less than 1 (delta phase at highest modulating frequency) which describes narrowband FM. In any case, the distinction between the two flavors is just a matter of degree, it is not fundamental. For broadcast normally wide band FM is used because of the signal quality benefits, while radio communication uses narrowband FM for spectrum efficiency, but both can be traced back to Armstrong.
Incidentally, Armstrong was not the original inventor of FM, though he arguably is the one whose work became known and led to what we use today. Hanso Idzerda in the Netherlands, the builder of broadcast station PCGG in 1919, invented and patented FM transmission and described its benefits for transmitter simplicity and efficiency. What he did not do (but Armstrong did) is describe receiver technology that takes advantage of the properties of FM, and the "slope detection" that Idzerda's listeners presumably used does not achieve those benefits. Paul Koning (talk) 18:55, 20 December 2017 (UTC)
The section titled "Sinusoidal baseband signal" begins, "Mathematically, a baseband modulated signal may be approximated by a sinusoidal continuous wave signal with a frequency fm". But what is a baseband modulated signal? Up till this point, a baseband signal is equated with a modulating signal. The "frequency fm", as opposed to fc, seems to confirm that we're talking about a baseband signal, i.e. the modulating signal, not the transmitted signal. Huttarl (talk) 15:24, 5 April 2018 (UTC)
The article says: contrast this with FM audio broadcasting, where the ratio is around 10,000. FM broadcasting, in the US at least, is around 100MHz. 10000:1 would be 10kHz. I believe without a stereo subcarrier, broadcast FM can go to 18KHz or so, as long as it is low enough at 19KHz not to trigger the stereo demodulator. With subcarriers such as SCA, it is up to 70KHz or more, so closer to 1400:1. Gah4 (talk) 22:45, 16 July 2018 (UTC)