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Sub-signal
Please explain what is meant by a station transmitting a sub-signal.
Thanks, Evan |
#2
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In article , FAZAMY wrote:
Please explain what is meant by a station transmitting a sub-signal. Do you mean subcarrier? --scott -- "C'est un Nagra. C'est suisse, et tres, tres precis." |
#3
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FAZAMY wrote:
Please explain what is meant by a station transmitting a sub-signal. I presume you mean a "subcarrier"? (also known as "SCA" in the States and "SCMO" in Canada) A very high-pitched signal (usually either 67 or 92KHz) is added to the audio before transmission. This high-pitched signal is modulated with additional information. In the early days of subcarriers, this "additional information" was a second audio program, usually background music. ("Muzak") More recently, it's been used for "talking books" for the visually impaired, and for various types of data transmission. These subcarrier transmissions are not intended for reception by the general public - indeed, I believe the Electronic Communications Privacy Act makes it *illegal* for non-subscribers to monitor subcarriers. Another data subcarrier at 57KHz is used for "RDS", a data transmission system that *is* intended for the general public. It transmits a continuous station ID, and can provide other information like format, frequencies of other transmitters carrying the same program, and a text string commonly used to show the name of the song being played. Actually, FM stereo depends on yet another subcarrier, at 38KHz. This subcarrier contains a mix of the right and left channels, with the right channel 180 degrees out of phase. Mix the 38KHz subcarrier with the monophonic signal transmitted the normal way, and the right channel cancels out and you get only the left. Flip the subcarrier 180 degrees out of phase, mix it with the monophonic signal, and the *left* channel cancels out and you get only the *right*. Feed each to a separate speaker and voila: stereo. -- Doug Smith W9WI Pleasant View (Nashville), TN EM66 http://www.w9wi.com |
#4
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--------------060603020300020905060107 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Doug Smith W9WI wrote: FAZAMY wrote: Please explain what is meant by a station transmitting a sub-signal. I presume you mean a "subcarrier"? (also known as "SCA" in the States and "SCMO" in Canada) A very high-pitched signal (usually either 67 or 92KHz) is added to the audio before transmission. This high-pitched signal is modulated with additional information. In the early days of subcarriers, this "additional information" was a second audio program, usually background music. ("Muzak") More recently, it's been used for "talking books" for the visually impaired, and for various types of data transmission. These subcarrier transmissions are not intended for reception by the general public - indeed, I believe the Electronic Communications Privacy Act makes it *illegal* for non-subscribers to monitor subcarriers. Another data subcarrier at 57KHz is used for "RDS", a data transmission system that *is* intended for the general public. It transmits a continuous station ID, and can provide other information like format, frequencies of other transmitters carrying the same program, and a text string commonly used to show the name of the song being played. Actually, FM stereo depends on yet another subcarrier, at 38KHz. This subcarrier contains a mix of the right and left channels, with the right channel 180 degrees out of phase. Mix the 38KHz subcarrier with the monophonic signal transmitted the normal way, and the right channel cancels out and you get only the left. Flip the sub carrier 180 degrees out of phase, mix it with the monophonic signal, and the *left* channel cancels out and you get only the *right*. Feed each to a separate speaker and voila: stereo. Actually there is no sub carrier at 38 kHz, just the sidebands as it is transmitted DSSC (Double sideband suppressed carrier). The 19 KHz pilot is locked to the original 38 kHz and is used in the receiver to reinsert the 38 kHz so to demodulate the sidebands. --------------060603020300020905060107 Content-Type: text/html; charset=us-ascii Content-Transfer-Encoding: 7bit !DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" html head title/title /head body Doug Smith W9WI wrote:br blockquote type="cite" " pre wrap=""FAZAMY wrote: /pre blockquote type="cite" pre wrap=""Please explain what is meant by a station transmitting a sub-signal. /pre /blockquote pre wrap=""!---- I presume you mean a "subcarrier"? (also known as "SCA" in the States and "SCMO" in Canada) A very high-pitched signal (usually either 67 or 92KHz) is added to the audio before transmission. This high-pitched signal is modulated with additional information. In the early days of subcarriers, this "additional information" was a second audio program, usually background music. ("Muzak") More recently, it's been used for "talking books" for the visually impaired, and for various types of data transmission. These subcarrier transmissions are not intended for reception by the general public - indeed, I believe the Electronic Communications Privacy Act makes it *illegal* for non-subscribers to monitor subcarriers. Another data subcarrier at 57KHz is used for "RDS", a data transmission system that *is* intended for the general public. It transmits a continuous station ID, and can provide other information like format, frequencies of other transmitters carrying the same program, and a text string commonly used to show the name of the song being played. Actually, FM stereo depends on yet another subcarrier, at 38KHz. This subcarrier contains a mix of the right and left channels, with the right channel 180 degrees out of phase. Mix the 38KHz subcarrier with the monophonic signal transmitted the normal way, and the right channel cancels out and you get only the left. Flip the sub carrier 180 degrees out of phase, mix it with the monophonic signal, and the *left* channel cancels out and you get only the *right*. Feed each to a separate speaker and voila: stereo. /pre /blockquote Actually there is no sub carrier at 38 kHz, just the sidebands as it is transmitted DSSC (Double sideband suppressed carrier). The 19 KHz pilot is locked to the original 38 kHz and is used in the receiver to reinsert the 38 kHz so to demodulate the sidebands.br /body /html --------------060603020300020905060107-- |
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