Talk:FM broadcasting
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[edit] History
This article used to have a lot of US-specific material. To fix that, the original article was moved (along with its history) to FM broadcasting in the USA, then the non-US specific material was restored here. Therefore much of the editing history is now at the new article. --Tony Sidaway|Talk 23:32, 14 Mar 2005 (UTC)
[edit] Definition of terms, clarity
I've linked to a number of terms (mostly used in the first paragraph after the introduction) which are technical jargon and undefined in the article. Some of those links probably don't go where they should.
I know a fair amount about radio, certainly well beyond what the average person knows, and I find major portions of this article fairly incomprehensible. It was obviously written by someone who knows the subject and is used to communicating with engineers, not with nonspecialists. Because of this and the undefined terms, I nearly slapped a "clarity" tag on the page. But maybe I'm just having a bad day. In any case, I suspect this article reads like a lot of the mathematics articles here - mostly obscure to those outside the high priesthood. --24.237.89.66 15:00, 6 January 2006 (UTC)
The article really seems as if it starts half-way through - as if there should be a simple "How FM broadcasting works" bit at the beginning, then all the technical jargon. Perhaps someone who understands the intricacies could work on 'FM 101'? Cammy 11:05, 10 January 2006 (UTC)
- That is covered by more fundamental articles on radio, broadcasting and frequency modulation. This article should not duplicate what is already written in those elementary articles, but instead concentrate on the specifics of FM as it is applied to broadcasting. Harumphy 12:14, 10 January 2006 (UTC)
[edit] Zenith/GE system Pilot tone system
Can anyone explain why 19 KHz was chosen as the pilot tone frequency for FM stereo and why it is necessary to have a such a wide (4KHz) guardband around the pilot tone. Surely a higher pilot tone frequency and/or a tighter guardband spec could be used to improve the audio bandwith beyond the 15KHz limit ?
Also I have heard there were/are rival systems to the Zenith/GE system. Does anyone know how these worked when/where the were/are used and how well they worked ?
- A higher pilot tone frequency would imply a higher stereo subcarrier frequency, which would make it more vulnerable to noise. A tighter guardband spec would require steeper filter slopes, adding to the cost and complexity of receivers. When it was developed, this system pushed the available technology to the limit. Harumphy 09:14, 23 July 2006 (UTC)
[edit] Basic concepts
Basic stuff about frequency modulation, that is not specific to FM broadcasting, surely belongs in the article about frequency modulation. It should not be duplicated here. This article should describe FM as applied to broadcasting, and not FM in general, IMHO. Therefore basic stuff about wide versus narrow FM, Carson's rule, etc., belongs there. Harumphy 15:49, 23 July 2006 (UTC)
[edit] Wide and narrow
The wide versus narrow thing is too simplistic, because in practice there is a wide variety of systems using a whole range of parameters which do not fit into narrow and wide camps. Where is the boundary between narrow and wide? How many kHz? Is an outside broadcast link, using 10 kHz peak deviation in a 50 kHz channel assignment to carry about 12 kHz of audio bandwidth wide or narrow? It may make more sense to talk of the modulation index, but again this belongs in the general FM article, not the FM broadcasting one. Harumphy 15:49, 23 July 2006 (UTC)
[edit] Why 87-108
Why is 87-108 (roughly) used for civilian FM broadcast? Who chose these frequencies? --81.105.251.160 01:53, 6 August 2006 (UTC)
- The radio spectrum is allocated to its various uses by international agreement, under the auspices of the International Telecommunications Union (a UN agency). These agreements are reached at a serious of conferences held (typically) every few years. Harumphy 08:13, 6 August 2006 (UTC).
[edit] Why "Non-Broadcast Uses?"
This article is focused on "FM Broadcasting", and, largely the technical details of the science. I propose that the section entitled "non-broadcast uses" be moved to its own article or deleted. In truth, there are many other uses of frequency-modulated RF carriers than broadcasting. Wireless two-way communication, amateur radio, and occasionally data communications (though FM is an inefficient use of spectrum for packet-type radio). It may be of more use to have a section under "[Frequency Modulation]" on "application" rather than a "non-broadcast" section under the "broadcasting" article.--Gdickinson 02:08, 12 August 2006 (UTC)
- I've changed the title to something a little less contradictory. IMHO the section should be kept because the uses listed are within the allocated FM band, using FM broadcast technology, and therefore are relevant to the article. By and large these uses are just extended uses of the standard band, generally one-way communications that would not necessarily be practical otherwise. It is true that a great deal of FM is used in two-way communications, but that doesn't mean that it belongs in this article. I am arguing that microtransmitters, however, do. Haikupoet 05:44, 12 August 2006 (UTC)
[edit] Wrong technical information about FM Stereo
The article states:
Stereo FM signals are far more susceptible to noise and multipath distortion than mono FM signals. This is due to several factors, including the following:
the addition of the two sidebands of the difference subcarrier to the baseband signal increases the noise bandwidth of the signal by a factor of three (9.5 dB) as compared with a mono signal. as mentioned above, the pre-emphasis is applied to the audio signals before encoding. This results in the pre-emphasis acting in the wrong direction on the lower sideband of the difference subcarrier, i.e. decreasing the level as the frequency rises, which will have a further deleterious effect on the S/N of the difference signal.
- This is quite obviously completely incorrect.
- The pilot tone is 10 percent, leaving 90 percent available for information. That is a -0.915150 dB reduction in available information (signal) over monophonic operation. Further, on the average, fifty percent of this information is in the subchannel, that's an additional -6.020600 dB reduction in information. The sum of these two shows the reduction of the available S/N over a mono signal is -6.935750 dB.
- Then, the argument of the 23 kHz to 53 kHz information having pre-emphasis in the wrong direction is further incorrect. This information in the subchannel cannot be broken up in such an illogical way. The subchannel contains a pair of sidebands, with the originating carrier suppressed at least 40 dB. This L-R information exists in both sidebands. They exists in a phase-linear, flat-frequency-response portion of the supersonic audio spectrum. Guessing that baseband preemphasis somehow affected this is not supported by mathematics or information theory. At one time in the United States, there were three FM Stereo generators available, that compiled with the FCC Rules and Regulations. All three were designed by me. The January, 1974 Broadcast Engineering magazine, on page 25 starts a three-page article that I wrote as an expert. --LymanSchool 03:41, 28 December 2006 (UTC)
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- It probably isn't all that helpful to argue about the S/N disadvantage of stereo signals, because there are so many variables that would need to be defined first. First, are we talking about S/N in the M channel, the S channel, or each or the L & R channels? Is the pre-emphasis 50 or 75 uS? Are we talking about unweighted or weighted noise? If the latter, A-weighted RMS, ITU-R 468 or something else? I suggest we should identify the sources of stereo noise without quantifying them. Harumphy 12:19, 28 December 2006 (UTC)
[edit] Conferences about FM
I added a small section about ITU conferences; don't you think we should expand that section? I can do it, if we think we could do it. [Hamlet 26 Mar 2007]
