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Microwave Spectrum - Amplitude Modulation
Why aren't there amplitude modulated stations in the high megahertz/gigahertz range?
What artifacts would arise? |
#2
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Microwave Spectrum - Amplitude Modulation
This isn't really an audio.tech question, but I'll give it a try anyway. Any
experts out there jump in and correct me. The better question is "why aren't there FM stations in the lower frequency bands?" Here's a brief history as best I can piece it together. AM transmitters are very simple designs. Ditto on the receivers. A diode, a small resistor and capacitor, a good antenna, a pair of headphones and you've got an AM receiver. Early vacuum tubes limited oscillators and amplifiers to low frequencies, so that's how the AM band got started. With better technology in all areas came the more sophisticated and complicated FM transmitters and receivers. FM also has the nice feature of rejecting static from man made and natural sources, resulting in a much more pleasing listening experience. Naturally, there was the drive for higher fidelity with the full audio frequency response (I think AM is limited to 5 Khz max, FM is 15 Khz). To broadcast this higher fidelity takes up a lot more room on the spectrum. In fact, the entire AM radio band could only carry maybe 2 FM stations. However, in the higher broadcast frequencies, say 100 Mhz, the 15Khz addition from the audio is a much less significant number. The technology to oscillate and amplify signals at the UHF and microwave spectrum is much more complicated and expensive than the low frequency stuff. What would then be the point of broadcasting the simple, static-prone AM over these more sophisticated systems? Having said that, television broadcast (at about 50 Mhz) is a hybrid with the picture sent AM and the sound sent FM. That's all changing now with all TV stations required to go digital (not high definition) by I think 2007. What about FM at the low frequencies? Yes, it is possible. But can you imagine every radio station and every consumer having to throw out their old equipment and get all new. For no real benefit (since the audio response would still be limited to the 5 Khz). Hope this answers your question... Mike "Curious" wrote in message om... Why aren't there amplitude modulated stations in the high megahertz/gigahertz range? What artifacts would arise? |
#3
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Microwave Spectrum - Amplitude Modulation
This isn't really an audio.tech question, but I'll give it a try anyway. Any
experts out there jump in and correct me. The better question is "why aren't there FM stations in the lower frequency bands?" Here's a brief history as best I can piece it together. AM transmitters are very simple designs. Ditto on the receivers. A diode, a small resistor and capacitor, a good antenna, a pair of headphones and you've got an AM receiver. Early vacuum tubes limited oscillators and amplifiers to low frequencies, so that's how the AM band got started. With better technology in all areas came the more sophisticated and complicated FM transmitters and receivers. FM also has the nice feature of rejecting static from man made and natural sources, resulting in a much more pleasing listening experience. Naturally, there was the drive for higher fidelity with the full audio frequency response (I think AM is limited to 5 Khz max, FM is 15 Khz). To broadcast this higher fidelity takes up a lot more room on the spectrum. In fact, the entire AM radio band could only carry maybe 2 FM stations. However, in the higher broadcast frequencies, say 100 Mhz, the 15Khz addition from the audio is a much less significant number. The technology to oscillate and amplify signals at the UHF and microwave spectrum is much more complicated and expensive than the low frequency stuff. What would then be the point of broadcasting the simple, static-prone AM over these more sophisticated systems? Having said that, television broadcast (at about 50 Mhz) is a hybrid with the picture sent AM and the sound sent FM. That's all changing now with all TV stations required to go digital (not high definition) by I think 2007. What about FM at the low frequencies? Yes, it is possible. But can you imagine every radio station and every consumer having to throw out their old equipment and get all new. For no real benefit (since the audio response would still be limited to the 5 Khz). Hope this answers your question... Mike "Curious" wrote in message om... Why aren't there amplitude modulated stations in the high megahertz/gigahertz range? What artifacts would arise? |
#4
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Microwave Spectrum - Amplitude Modulation
This isn't really an audio.tech question, but I'll give it a try anyway. Any
experts out there jump in and correct me. The better question is "why aren't there FM stations in the lower frequency bands?" Here's a brief history as best I can piece it together. AM transmitters are very simple designs. Ditto on the receivers. A diode, a small resistor and capacitor, a good antenna, a pair of headphones and you've got an AM receiver. Early vacuum tubes limited oscillators and amplifiers to low frequencies, so that's how the AM band got started. With better technology in all areas came the more sophisticated and complicated FM transmitters and receivers. FM also has the nice feature of rejecting static from man made and natural sources, resulting in a much more pleasing listening experience. Naturally, there was the drive for higher fidelity with the full audio frequency response (I think AM is limited to 5 Khz max, FM is 15 Khz). To broadcast this higher fidelity takes up a lot more room on the spectrum. In fact, the entire AM radio band could only carry maybe 2 FM stations. However, in the higher broadcast frequencies, say 100 Mhz, the 15Khz addition from the audio is a much less significant number. The technology to oscillate and amplify signals at the UHF and microwave spectrum is much more complicated and expensive than the low frequency stuff. What would then be the point of broadcasting the simple, static-prone AM over these more sophisticated systems? Having said that, television broadcast (at about 50 Mhz) is a hybrid with the picture sent AM and the sound sent FM. That's all changing now with all TV stations required to go digital (not high definition) by I think 2007. What about FM at the low frequencies? Yes, it is possible. But can you imagine every radio station and every consumer having to throw out their old equipment and get all new. For no real benefit (since the audio response would still be limited to the 5 Khz). Hope this answers your question... Mike "Curious" wrote in message om... Why aren't there amplitude modulated stations in the high megahertz/gigahertz range? What artifacts would arise? |
#5
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Microwave Spectrum - Amplitude Modulation
This isn't really an audio.tech question, but I'll give it a try anyway. Any
experts out there jump in and correct me. The better question is "why aren't there FM stations in the lower frequency bands?" Here's a brief history as best I can piece it together. AM transmitters are very simple designs. Ditto on the receivers. A diode, a small resistor and capacitor, a good antenna, a pair of headphones and you've got an AM receiver. Early vacuum tubes limited oscillators and amplifiers to low frequencies, so that's how the AM band got started. With better technology in all areas came the more sophisticated and complicated FM transmitters and receivers. FM also has the nice feature of rejecting static from man made and natural sources, resulting in a much more pleasing listening experience. Naturally, there was the drive for higher fidelity with the full audio frequency response (I think AM is limited to 5 Khz max, FM is 15 Khz). To broadcast this higher fidelity takes up a lot more room on the spectrum. In fact, the entire AM radio band could only carry maybe 2 FM stations. However, in the higher broadcast frequencies, say 100 Mhz, the 15Khz addition from the audio is a much less significant number. The technology to oscillate and amplify signals at the UHF and microwave spectrum is much more complicated and expensive than the low frequency stuff. What would then be the point of broadcasting the simple, static-prone AM over these more sophisticated systems? Having said that, television broadcast (at about 50 Mhz) is a hybrid with the picture sent AM and the sound sent FM. That's all changing now with all TV stations required to go digital (not high definition) by I think 2007. What about FM at the low frequencies? Yes, it is possible. But can you imagine every radio station and every consumer having to throw out their old equipment and get all new. For no real benefit (since the audio response would still be limited to the 5 Khz). Hope this answers your question... Mike "Curious" wrote in message om... Why aren't there amplitude modulated stations in the high megahertz/gigahertz range? What artifacts would arise? |
#6
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Microwave Spectrum - Amplitude Modulation
The standard broadcast AM stations in the broadcast band are a total of 10
kHz wide (+- 5 kHz referenced to centre band of received broadcast station). The international short-wave broadcast stations are a total of 5 kHz wide (+-2.5 kHz referenced to centre band of received short-wave broadcast station). At the -3 Db point in reference to the centre of the carrier would be the determination of the bandwidth. -- Greetings, Jerry Greenberg GLG Technologies GLG ========================================= WebPage http://www.zoom-one.com Electronics http://www.zoom-one.com/electron.htm ========================================= "Mike Metzger" wrote in message .com... This isn't really an audio.tech question, but I'll give it a try anyway. Any experts out there jump in and correct me. The better question is "why aren't there FM stations in the lower frequency bands?" Here's a brief history as best I can piece it together. AM transmitters are very simple designs. Ditto on the receivers. A diode, a small resistor and capacitor, a good antenna, a pair of headphones and you've got an AM receiver. Early vacuum tubes limited oscillators and amplifiers to low frequencies, so that's how the AM band got started. With better technology in all areas came the more sophisticated and complicated FM transmitters and receivers. FM also has the nice feature of rejecting static from man made and natural sources, resulting in a much more pleasing listening experience. Naturally, there was the drive for higher fidelity with the full audio frequency response (I think AM is limited to 5 Khz max, FM is 15 Khz). To broadcast this higher fidelity takes up a lot more room on the spectrum. In fact, the entire AM radio band could only carry maybe 2 FM stations. However, in the higher broadcast frequencies, say 100 Mhz, the 15Khz addition from the audio is a much less significant number. The technology to oscillate and amplify signals at the UHF and microwave spectrum is much more complicated and expensive than the low frequency stuff. What would then be the point of broadcasting the simple, static-prone AM over these more sophisticated systems? Having said that, television broadcast (at about 50 Mhz) is a hybrid with the picture sent AM and the sound sent FM. That's all changing now with all TV stations required to go digital (not high definition) by I think 2007. What about FM at the low frequencies? Yes, it is possible. But can you imagine every radio station and every consumer having to throw out their old equipment and get all new. For no real benefit (since the audio response would still be limited to the 5 Khz). Hope this answers your question... Mike "Curious" wrote in message om... Why aren't there amplitude modulated stations in the high megahertz/gigahertz range? What artifacts would arise? |
#7
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Microwave Spectrum - Amplitude Modulation
The standard broadcast AM stations in the broadcast band are a total of 10
kHz wide (+- 5 kHz referenced to centre band of received broadcast station). The international short-wave broadcast stations are a total of 5 kHz wide (+-2.5 kHz referenced to centre band of received short-wave broadcast station). At the -3 Db point in reference to the centre of the carrier would be the determination of the bandwidth. -- Greetings, Jerry Greenberg GLG Technologies GLG ========================================= WebPage http://www.zoom-one.com Electronics http://www.zoom-one.com/electron.htm ========================================= "Mike Metzger" wrote in message .com... This isn't really an audio.tech question, but I'll give it a try anyway. Any experts out there jump in and correct me. The better question is "why aren't there FM stations in the lower frequency bands?" Here's a brief history as best I can piece it together. AM transmitters are very simple designs. Ditto on the receivers. A diode, a small resistor and capacitor, a good antenna, a pair of headphones and you've got an AM receiver. Early vacuum tubes limited oscillators and amplifiers to low frequencies, so that's how the AM band got started. With better technology in all areas came the more sophisticated and complicated FM transmitters and receivers. FM also has the nice feature of rejecting static from man made and natural sources, resulting in a much more pleasing listening experience. Naturally, there was the drive for higher fidelity with the full audio frequency response (I think AM is limited to 5 Khz max, FM is 15 Khz). To broadcast this higher fidelity takes up a lot more room on the spectrum. In fact, the entire AM radio band could only carry maybe 2 FM stations. However, in the higher broadcast frequencies, say 100 Mhz, the 15Khz addition from the audio is a much less significant number. The technology to oscillate and amplify signals at the UHF and microwave spectrum is much more complicated and expensive than the low frequency stuff. What would then be the point of broadcasting the simple, static-prone AM over these more sophisticated systems? Having said that, television broadcast (at about 50 Mhz) is a hybrid with the picture sent AM and the sound sent FM. That's all changing now with all TV stations required to go digital (not high definition) by I think 2007. What about FM at the low frequencies? Yes, it is possible. But can you imagine every radio station and every consumer having to throw out their old equipment and get all new. For no real benefit (since the audio response would still be limited to the 5 Khz). Hope this answers your question... Mike "Curious" wrote in message om... Why aren't there amplitude modulated stations in the high megahertz/gigahertz range? What artifacts would arise? |
#8
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Microwave Spectrum - Amplitude Modulation
The standard broadcast AM stations in the broadcast band are a total of 10
kHz wide (+- 5 kHz referenced to centre band of received broadcast station). The international short-wave broadcast stations are a total of 5 kHz wide (+-2.5 kHz referenced to centre band of received short-wave broadcast station). At the -3 Db point in reference to the centre of the carrier would be the determination of the bandwidth. -- Greetings, Jerry Greenberg GLG Technologies GLG ========================================= WebPage http://www.zoom-one.com Electronics http://www.zoom-one.com/electron.htm ========================================= "Mike Metzger" wrote in message .com... This isn't really an audio.tech question, but I'll give it a try anyway. Any experts out there jump in and correct me. The better question is "why aren't there FM stations in the lower frequency bands?" Here's a brief history as best I can piece it together. AM transmitters are very simple designs. Ditto on the receivers. A diode, a small resistor and capacitor, a good antenna, a pair of headphones and you've got an AM receiver. Early vacuum tubes limited oscillators and amplifiers to low frequencies, so that's how the AM band got started. With better technology in all areas came the more sophisticated and complicated FM transmitters and receivers. FM also has the nice feature of rejecting static from man made and natural sources, resulting in a much more pleasing listening experience. Naturally, there was the drive for higher fidelity with the full audio frequency response (I think AM is limited to 5 Khz max, FM is 15 Khz). To broadcast this higher fidelity takes up a lot more room on the spectrum. In fact, the entire AM radio band could only carry maybe 2 FM stations. However, in the higher broadcast frequencies, say 100 Mhz, the 15Khz addition from the audio is a much less significant number. The technology to oscillate and amplify signals at the UHF and microwave spectrum is much more complicated and expensive than the low frequency stuff. What would then be the point of broadcasting the simple, static-prone AM over these more sophisticated systems? Having said that, television broadcast (at about 50 Mhz) is a hybrid with the picture sent AM and the sound sent FM. That's all changing now with all TV stations required to go digital (not high definition) by I think 2007. What about FM at the low frequencies? Yes, it is possible. But can you imagine every radio station and every consumer having to throw out their old equipment and get all new. For no real benefit (since the audio response would still be limited to the 5 Khz). Hope this answers your question... Mike "Curious" wrote in message om... Why aren't there amplitude modulated stations in the high megahertz/gigahertz range? What artifacts would arise? |
#9
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Microwave Spectrum - Amplitude Modulation
The standard broadcast AM stations in the broadcast band are a total of 10
kHz wide (+- 5 kHz referenced to centre band of received broadcast station). The international short-wave broadcast stations are a total of 5 kHz wide (+-2.5 kHz referenced to centre band of received short-wave broadcast station). At the -3 Db point in reference to the centre of the carrier would be the determination of the bandwidth. -- Greetings, Jerry Greenberg GLG Technologies GLG ========================================= WebPage http://www.zoom-one.com Electronics http://www.zoom-one.com/electron.htm ========================================= "Mike Metzger" wrote in message .com... This isn't really an audio.tech question, but I'll give it a try anyway. Any experts out there jump in and correct me. The better question is "why aren't there FM stations in the lower frequency bands?" Here's a brief history as best I can piece it together. AM transmitters are very simple designs. Ditto on the receivers. A diode, a small resistor and capacitor, a good antenna, a pair of headphones and you've got an AM receiver. Early vacuum tubes limited oscillators and amplifiers to low frequencies, so that's how the AM band got started. With better technology in all areas came the more sophisticated and complicated FM transmitters and receivers. FM also has the nice feature of rejecting static from man made and natural sources, resulting in a much more pleasing listening experience. Naturally, there was the drive for higher fidelity with the full audio frequency response (I think AM is limited to 5 Khz max, FM is 15 Khz). To broadcast this higher fidelity takes up a lot more room on the spectrum. In fact, the entire AM radio band could only carry maybe 2 FM stations. However, in the higher broadcast frequencies, say 100 Mhz, the 15Khz addition from the audio is a much less significant number. The technology to oscillate and amplify signals at the UHF and microwave spectrum is much more complicated and expensive than the low frequency stuff. What would then be the point of broadcasting the simple, static-prone AM over these more sophisticated systems? Having said that, television broadcast (at about 50 Mhz) is a hybrid with the picture sent AM and the sound sent FM. That's all changing now with all TV stations required to go digital (not high definition) by I think 2007. What about FM at the low frequencies? Yes, it is possible. But can you imagine every radio station and every consumer having to throw out their old equipment and get all new. For no real benefit (since the audio response would still be limited to the 5 Khz). Hope this answers your question... Mike "Curious" wrote in message om... Why aren't there amplitude modulated stations in the high megahertz/gigahertz range? What artifacts would arise? |
#10
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Microwave Spectrum - Amplitude Modulation
"Mike Metzger" wrote in message y.com...
This isn't really an audio.tech question, but I'll give it a try anyway. Any experts out there jump in and correct me. The better question is "why aren't there FM stations in the lower frequency bands?" FM stations are not in the lower-frequuency bands because FM require more bandwidth than AM and lower-frequencies don't have the bandwidth to handle FM. Now the reverse... What artifacts would affect AM stations in the FM band? Considering that most electric/electronic equipment work in the lower-frequency range (e.g. 50-60Hz), wouldn't higher frequencies be less vulnerable to static? |
#11
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Microwave Spectrum - Amplitude Modulation
"Mike Metzger" wrote in message y.com...
This isn't really an audio.tech question, but I'll give it a try anyway. Any experts out there jump in and correct me. The better question is "why aren't there FM stations in the lower frequency bands?" FM stations are not in the lower-frequuency bands because FM require more bandwidth than AM and lower-frequencies don't have the bandwidth to handle FM. Now the reverse... What artifacts would affect AM stations in the FM band? Considering that most electric/electronic equipment work in the lower-frequency range (e.g. 50-60Hz), wouldn't higher frequencies be less vulnerable to static? |
#12
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Microwave Spectrum - Amplitude Modulation
"Mike Metzger" wrote in message y.com...
This isn't really an audio.tech question, but I'll give it a try anyway. Any experts out there jump in and correct me. The better question is "why aren't there FM stations in the lower frequency bands?" FM stations are not in the lower-frequuency bands because FM require more bandwidth than AM and lower-frequencies don't have the bandwidth to handle FM. Now the reverse... What artifacts would affect AM stations in the FM band? Considering that most electric/electronic equipment work in the lower-frequency range (e.g. 50-60Hz), wouldn't higher frequencies be less vulnerable to static? |
#13
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Microwave Spectrum - Amplitude Modulation
"Mike Metzger" wrote in message y.com...
This isn't really an audio.tech question, but I'll give it a try anyway. Any experts out there jump in and correct me. The better question is "why aren't there FM stations in the lower frequency bands?" FM stations are not in the lower-frequuency bands because FM require more bandwidth than AM and lower-frequencies don't have the bandwidth to handle FM. Now the reverse... What artifacts would affect AM stations in the FM band? Considering that most electric/electronic equipment work in the lower-frequency range (e.g. 50-60Hz), wouldn't higher frequencies be less vulnerable to static? |
#14
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Microwave Spectrum - Amplitude Modulation
On Sat, 21 Feb 2004 03:17:13 -0500, "Jerry G."
wrote: The standard broadcast AM stations in the broadcast band are a total of 10 kHz wide (+- 5 kHz referenced to centre band of received broadcast station). The international short-wave broadcast stations are a total of 5 kHz wide (+-2.5 kHz referenced to centre band of received short-wave broadcast station). At the -3 Db point in reference to the centre of the carrier would be the determination of the bandwidth. These are the numbers for AM. The bandwidth of the modulation simply requires the double of the bandwidth for transmission. If the carrier frequency is 1.000 MHz and the maximum audio frequency to be trans- mitted is 5 kHz, the broadcast signal extends from 995 kHz through 1005 kHz. The dynamic range of the received signal is just the ratio between the received power of the signal and the received power of noise. FM is quite different: The bandwidth of the broadcast signal is determined by the amplitude of the signal, not by its frequency. Usually the bandwidth is 100 kHz, both for mono and for stereo broadcast. For a mono broadcast the upper frequency limit is about 15 kHz, for a stereo broadcast the highest frequency is 53 kHz. In theory the bandwith of a FM signal is infinite. The more you limit it the more distortion is introduced *and* the signal to noise ration is degraded. Thus, the 100 kHz signal width of FM is a compromise between the number of channels that fit into a given band and the signal to noise ration and distortion. S/N is about 70 dB, distortion is about 0.05% (these are practical numbers, not theoretical numbers). HTH Norbert |
#15
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Microwave Spectrum - Amplitude Modulation
On Sat, 21 Feb 2004 03:17:13 -0500, "Jerry G."
wrote: The standard broadcast AM stations in the broadcast band are a total of 10 kHz wide (+- 5 kHz referenced to centre band of received broadcast station). The international short-wave broadcast stations are a total of 5 kHz wide (+-2.5 kHz referenced to centre band of received short-wave broadcast station). At the -3 Db point in reference to the centre of the carrier would be the determination of the bandwidth. These are the numbers for AM. The bandwidth of the modulation simply requires the double of the bandwidth for transmission. If the carrier frequency is 1.000 MHz and the maximum audio frequency to be trans- mitted is 5 kHz, the broadcast signal extends from 995 kHz through 1005 kHz. The dynamic range of the received signal is just the ratio between the received power of the signal and the received power of noise. FM is quite different: The bandwidth of the broadcast signal is determined by the amplitude of the signal, not by its frequency. Usually the bandwidth is 100 kHz, both for mono and for stereo broadcast. For a mono broadcast the upper frequency limit is about 15 kHz, for a stereo broadcast the highest frequency is 53 kHz. In theory the bandwith of a FM signal is infinite. The more you limit it the more distortion is introduced *and* the signal to noise ration is degraded. Thus, the 100 kHz signal width of FM is a compromise between the number of channels that fit into a given band and the signal to noise ration and distortion. S/N is about 70 dB, distortion is about 0.05% (these are practical numbers, not theoretical numbers). HTH Norbert |
#16
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Microwave Spectrum - Amplitude Modulation
On Sat, 21 Feb 2004 03:17:13 -0500, "Jerry G."
wrote: The standard broadcast AM stations in the broadcast band are a total of 10 kHz wide (+- 5 kHz referenced to centre band of received broadcast station). The international short-wave broadcast stations are a total of 5 kHz wide (+-2.5 kHz referenced to centre band of received short-wave broadcast station). At the -3 Db point in reference to the centre of the carrier would be the determination of the bandwidth. These are the numbers for AM. The bandwidth of the modulation simply requires the double of the bandwidth for transmission. If the carrier frequency is 1.000 MHz and the maximum audio frequency to be trans- mitted is 5 kHz, the broadcast signal extends from 995 kHz through 1005 kHz. The dynamic range of the received signal is just the ratio between the received power of the signal and the received power of noise. FM is quite different: The bandwidth of the broadcast signal is determined by the amplitude of the signal, not by its frequency. Usually the bandwidth is 100 kHz, both for mono and for stereo broadcast. For a mono broadcast the upper frequency limit is about 15 kHz, for a stereo broadcast the highest frequency is 53 kHz. In theory the bandwith of a FM signal is infinite. The more you limit it the more distortion is introduced *and* the signal to noise ration is degraded. Thus, the 100 kHz signal width of FM is a compromise between the number of channels that fit into a given band and the signal to noise ration and distortion. S/N is about 70 dB, distortion is about 0.05% (these are practical numbers, not theoretical numbers). HTH Norbert |
#17
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Microwave Spectrum - Amplitude Modulation
On Sat, 21 Feb 2004 03:17:13 -0500, "Jerry G."
wrote: The standard broadcast AM stations in the broadcast band are a total of 10 kHz wide (+- 5 kHz referenced to centre band of received broadcast station). The international short-wave broadcast stations are a total of 5 kHz wide (+-2.5 kHz referenced to centre band of received short-wave broadcast station). At the -3 Db point in reference to the centre of the carrier would be the determination of the bandwidth. These are the numbers for AM. The bandwidth of the modulation simply requires the double of the bandwidth for transmission. If the carrier frequency is 1.000 MHz and the maximum audio frequency to be trans- mitted is 5 kHz, the broadcast signal extends from 995 kHz through 1005 kHz. The dynamic range of the received signal is just the ratio between the received power of the signal and the received power of noise. FM is quite different: The bandwidth of the broadcast signal is determined by the amplitude of the signal, not by its frequency. Usually the bandwidth is 100 kHz, both for mono and for stereo broadcast. For a mono broadcast the upper frequency limit is about 15 kHz, for a stereo broadcast the highest frequency is 53 kHz. In theory the bandwith of a FM signal is infinite. The more you limit it the more distortion is introduced *and* the signal to noise ration is degraded. Thus, the 100 kHz signal width of FM is a compromise between the number of channels that fit into a given band and the signal to noise ration and distortion. S/N is about 70 dB, distortion is about 0.05% (these are practical numbers, not theoretical numbers). HTH Norbert |
#18
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Microwave Spectrum - Amplitude Modulation
In the US commercial AM band, frequencies are allocated on 10kHz intervals,
but the transmitters themselves are allowed to modulate with audio frequencies up to 10kHz. That means the sidebands of adjacent channels will overlap, resulting in so-called "monkey chatter" that occurs when listening at night. You're hearing the inverted spectrum from stations on the adjacent channels. Furthermore, the carrier from the adjacent channels will "look" like 10kHz sidebands, which creates the familiar 10kHz whistle you hear on AM at night. There is no overlap between alternate channels, which are separated by 20kHz. The FCC tries to allocate frequencies on alternate channels between locally situated transmitters. During the day, when there is no "skip" from distant transmitters, you don't hear adjacent channel interference. "Jerry G." wrote in message ... The standard broadcast AM stations in the broadcast band are a total of 10 kHz wide (+- 5 kHz referenced to centre band of received broadcast station). The international short-wave broadcast stations are a total of 5 kHz wide (+-2.5 kHz referenced to centre band of received short-wave broadcast station). At the -3 Db point in reference to the centre of the carrier would be the determination of the bandwidth. -- Greetings, Jerry Greenberg GLG Technologies GLG ========================================= WebPage http://www.zoom-one.com Electronics http://www.zoom-one.com/electron.htm ========================================= "Mike Metzger" wrote in message .com... This isn't really an audio.tech question, but I'll give it a try anyway. Any experts out there jump in and correct me. The better question is "why aren't there FM stations in the lower frequency bands?" Here's a brief history as best I can piece it together. AM transmitters are very simple designs. Ditto on the receivers. A diode, a small resistor and capacitor, a good antenna, a pair of headphones and you've got an AM receiver. Early vacuum tubes limited oscillators and amplifiers to low frequencies, so that's how the AM band got started. With better technology in all areas came the more sophisticated and complicated FM transmitters and receivers. FM also has the nice feature of rejecting static from man made and natural sources, resulting in a much more pleasing listening experience. Naturally, there was the drive for higher fidelity with the full audio frequency response (I think AM is limited to 5 Khz max, FM is 15 Khz). To broadcast this higher fidelity takes up a lot more room on the spectrum. In fact, the entire AM radio band could only carry maybe 2 FM stations. However, in the higher broadcast frequencies, say 100 Mhz, the 15Khz addition from the audio is a much less significant number. The technology to oscillate and amplify signals at the UHF and microwave spectrum is much more complicated and expensive than the low frequency stuff. What would then be the point of broadcasting the simple, static-prone AM over these more sophisticated systems? Having said that, television broadcast (at about 50 Mhz) is a hybrid with the picture sent AM and the sound sent FM. That's all changing now with all TV stations required to go digital (not high definition) by I think 2007. What about FM at the low frequencies? Yes, it is possible. But can you imagine every radio station and every consumer having to throw out their old equipment and get all new. For no real benefit (since the audio response would still be limited to the 5 Khz). Hope this answers your question... Mike "Curious" wrote in message om... Why aren't there amplitude modulated stations in the high megahertz/gigahertz range? What artifacts would arise? |
#19
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Microwave Spectrum - Amplitude Modulation
In the US commercial AM band, frequencies are allocated on 10kHz intervals,
but the transmitters themselves are allowed to modulate with audio frequencies up to 10kHz. That means the sidebands of adjacent channels will overlap, resulting in so-called "monkey chatter" that occurs when listening at night. You're hearing the inverted spectrum from stations on the adjacent channels. Furthermore, the carrier from the adjacent channels will "look" like 10kHz sidebands, which creates the familiar 10kHz whistle you hear on AM at night. There is no overlap between alternate channels, which are separated by 20kHz. The FCC tries to allocate frequencies on alternate channels between locally situated transmitters. During the day, when there is no "skip" from distant transmitters, you don't hear adjacent channel interference. "Jerry G." wrote in message ... The standard broadcast AM stations in the broadcast band are a total of 10 kHz wide (+- 5 kHz referenced to centre band of received broadcast station). The international short-wave broadcast stations are a total of 5 kHz wide (+-2.5 kHz referenced to centre band of received short-wave broadcast station). At the -3 Db point in reference to the centre of the carrier would be the determination of the bandwidth. -- Greetings, Jerry Greenberg GLG Technologies GLG ========================================= WebPage http://www.zoom-one.com Electronics http://www.zoom-one.com/electron.htm ========================================= "Mike Metzger" wrote in message .com... This isn't really an audio.tech question, but I'll give it a try anyway. Any experts out there jump in and correct me. The better question is "why aren't there FM stations in the lower frequency bands?" Here's a brief history as best I can piece it together. AM transmitters are very simple designs. Ditto on the receivers. A diode, a small resistor and capacitor, a good antenna, a pair of headphones and you've got an AM receiver. Early vacuum tubes limited oscillators and amplifiers to low frequencies, so that's how the AM band got started. With better technology in all areas came the more sophisticated and complicated FM transmitters and receivers. FM also has the nice feature of rejecting static from man made and natural sources, resulting in a much more pleasing listening experience. Naturally, there was the drive for higher fidelity with the full audio frequency response (I think AM is limited to 5 Khz max, FM is 15 Khz). To broadcast this higher fidelity takes up a lot more room on the spectrum. In fact, the entire AM radio band could only carry maybe 2 FM stations. However, in the higher broadcast frequencies, say 100 Mhz, the 15Khz addition from the audio is a much less significant number. The technology to oscillate and amplify signals at the UHF and microwave spectrum is much more complicated and expensive than the low frequency stuff. What would then be the point of broadcasting the simple, static-prone AM over these more sophisticated systems? Having said that, television broadcast (at about 50 Mhz) is a hybrid with the picture sent AM and the sound sent FM. That's all changing now with all TV stations required to go digital (not high definition) by I think 2007. What about FM at the low frequencies? Yes, it is possible. But can you imagine every radio station and every consumer having to throw out their old equipment and get all new. For no real benefit (since the audio response would still be limited to the 5 Khz). Hope this answers your question... Mike "Curious" wrote in message om... Why aren't there amplitude modulated stations in the high megahertz/gigahertz range? What artifacts would arise? |
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Microwave Spectrum - Amplitude Modulation
In the US commercial AM band, frequencies are allocated on 10kHz intervals,
but the transmitters themselves are allowed to modulate with audio frequencies up to 10kHz. That means the sidebands of adjacent channels will overlap, resulting in so-called "monkey chatter" that occurs when listening at night. You're hearing the inverted spectrum from stations on the adjacent channels. Furthermore, the carrier from the adjacent channels will "look" like 10kHz sidebands, which creates the familiar 10kHz whistle you hear on AM at night. There is no overlap between alternate channels, which are separated by 20kHz. The FCC tries to allocate frequencies on alternate channels between locally situated transmitters. During the day, when there is no "skip" from distant transmitters, you don't hear adjacent channel interference. "Jerry G." wrote in message ... The standard broadcast AM stations in the broadcast band are a total of 10 kHz wide (+- 5 kHz referenced to centre band of received broadcast station). The international short-wave broadcast stations are a total of 5 kHz wide (+-2.5 kHz referenced to centre band of received short-wave broadcast station). At the -3 Db point in reference to the centre of the carrier would be the determination of the bandwidth. -- Greetings, Jerry Greenberg GLG Technologies GLG ========================================= WebPage http://www.zoom-one.com Electronics http://www.zoom-one.com/electron.htm ========================================= "Mike Metzger" wrote in message .com... This isn't really an audio.tech question, but I'll give it a try anyway. Any experts out there jump in and correct me. The better question is "why aren't there FM stations in the lower frequency bands?" Here's a brief history as best I can piece it together. AM transmitters are very simple designs. Ditto on the receivers. A diode, a small resistor and capacitor, a good antenna, a pair of headphones and you've got an AM receiver. Early vacuum tubes limited oscillators and amplifiers to low frequencies, so that's how the AM band got started. With better technology in all areas came the more sophisticated and complicated FM transmitters and receivers. FM also has the nice feature of rejecting static from man made and natural sources, resulting in a much more pleasing listening experience. Naturally, there was the drive for higher fidelity with the full audio frequency response (I think AM is limited to 5 Khz max, FM is 15 Khz). To broadcast this higher fidelity takes up a lot more room on the spectrum. In fact, the entire AM radio band could only carry maybe 2 FM stations. However, in the higher broadcast frequencies, say 100 Mhz, the 15Khz addition from the audio is a much less significant number. The technology to oscillate and amplify signals at the UHF and microwave spectrum is much more complicated and expensive than the low frequency stuff. What would then be the point of broadcasting the simple, static-prone AM over these more sophisticated systems? Having said that, television broadcast (at about 50 Mhz) is a hybrid with the picture sent AM and the sound sent FM. That's all changing now with all TV stations required to go digital (not high definition) by I think 2007. What about FM at the low frequencies? Yes, it is possible. But can you imagine every radio station and every consumer having to throw out their old equipment and get all new. For no real benefit (since the audio response would still be limited to the 5 Khz). Hope this answers your question... Mike "Curious" wrote in message om... Why aren't there amplitude modulated stations in the high megahertz/gigahertz range? What artifacts would arise? |
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Microwave Spectrum - Amplitude Modulation
In the US commercial AM band, frequencies are allocated on 10kHz intervals,
but the transmitters themselves are allowed to modulate with audio frequencies up to 10kHz. That means the sidebands of adjacent channels will overlap, resulting in so-called "monkey chatter" that occurs when listening at night. You're hearing the inverted spectrum from stations on the adjacent channels. Furthermore, the carrier from the adjacent channels will "look" like 10kHz sidebands, which creates the familiar 10kHz whistle you hear on AM at night. There is no overlap between alternate channels, which are separated by 20kHz. The FCC tries to allocate frequencies on alternate channels between locally situated transmitters. During the day, when there is no "skip" from distant transmitters, you don't hear adjacent channel interference. "Jerry G." wrote in message ... The standard broadcast AM stations in the broadcast band are a total of 10 kHz wide (+- 5 kHz referenced to centre band of received broadcast station). The international short-wave broadcast stations are a total of 5 kHz wide (+-2.5 kHz referenced to centre band of received short-wave broadcast station). At the -3 Db point in reference to the centre of the carrier would be the determination of the bandwidth. -- Greetings, Jerry Greenberg GLG Technologies GLG ========================================= WebPage http://www.zoom-one.com Electronics http://www.zoom-one.com/electron.htm ========================================= "Mike Metzger" wrote in message .com... This isn't really an audio.tech question, but I'll give it a try anyway. Any experts out there jump in and correct me. The better question is "why aren't there FM stations in the lower frequency bands?" Here's a brief history as best I can piece it together. AM transmitters are very simple designs. Ditto on the receivers. A diode, a small resistor and capacitor, a good antenna, a pair of headphones and you've got an AM receiver. Early vacuum tubes limited oscillators and amplifiers to low frequencies, so that's how the AM band got started. With better technology in all areas came the more sophisticated and complicated FM transmitters and receivers. FM also has the nice feature of rejecting static from man made and natural sources, resulting in a much more pleasing listening experience. Naturally, there was the drive for higher fidelity with the full audio frequency response (I think AM is limited to 5 Khz max, FM is 15 Khz). To broadcast this higher fidelity takes up a lot more room on the spectrum. In fact, the entire AM radio band could only carry maybe 2 FM stations. However, in the higher broadcast frequencies, say 100 Mhz, the 15Khz addition from the audio is a much less significant number. The technology to oscillate and amplify signals at the UHF and microwave spectrum is much more complicated and expensive than the low frequency stuff. What would then be the point of broadcasting the simple, static-prone AM over these more sophisticated systems? Having said that, television broadcast (at about 50 Mhz) is a hybrid with the picture sent AM and the sound sent FM. That's all changing now with all TV stations required to go digital (not high definition) by I think 2007. What about FM at the low frequencies? Yes, it is possible. But can you imagine every radio station and every consumer having to throw out their old equipment and get all new. For no real benefit (since the audio response would still be limited to the 5 Khz). Hope this answers your question... Mike "Curious" wrote in message om... Why aren't there amplitude modulated stations in the high megahertz/gigahertz range? What artifacts would arise? |
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Microwave Spectrum - Amplitude Modulation
Hey Don, now *I'm* curious.
I designed a TV transmitter for a middle eastern operator. It worked at 12GHz and covered to the horizon in all directions with a power of only 3 watts. This was angle modulated. 1. Was this 12 Ghz a microwave uplink or what? Obviously your standard TV set isn't going to receive a 12 Ghz signal. 2. I have been told by TV engineers that the higher frequencies don't have near the coverage per watt that the low ones do. With this changeover in the US to digital the FCC is assigning new digital channels by lottery. There was a local TV station that had a VHF channel on analog and got assigned a UHF for the digital. They now are using twice the KWs and are spending twice the money on electricity running their new transmitter to get the same coverage area they had with the VHF. Can you clarify? Mike Metzger |
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Microwave Spectrum - Amplitude Modulation
Hey Don, now *I'm* curious.
I designed a TV transmitter for a middle eastern operator. It worked at 12GHz and covered to the horizon in all directions with a power of only 3 watts. This was angle modulated. 1. Was this 12 Ghz a microwave uplink or what? Obviously your standard TV set isn't going to receive a 12 Ghz signal. 2. I have been told by TV engineers that the higher frequencies don't have near the coverage per watt that the low ones do. With this changeover in the US to digital the FCC is assigning new digital channels by lottery. There was a local TV station that had a VHF channel on analog and got assigned a UHF for the digital. They now are using twice the KWs and are spending twice the money on electricity running their new transmitter to get the same coverage area they had with the VHF. Can you clarify? Mike Metzger |
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Microwave Spectrum - Amplitude Modulation
Hey Don, now *I'm* curious.
I designed a TV transmitter for a middle eastern operator. It worked at 12GHz and covered to the horizon in all directions with a power of only 3 watts. This was angle modulated. 1. Was this 12 Ghz a microwave uplink or what? Obviously your standard TV set isn't going to receive a 12 Ghz signal. 2. I have been told by TV engineers that the higher frequencies don't have near the coverage per watt that the low ones do. With this changeover in the US to digital the FCC is assigning new digital channels by lottery. There was a local TV station that had a VHF channel on analog and got assigned a UHF for the digital. They now are using twice the KWs and are spending twice the money on electricity running their new transmitter to get the same coverage area they had with the VHF. Can you clarify? Mike Metzger |
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Microwave Spectrum - Amplitude Modulation
Hey Don, now *I'm* curious.
I designed a TV transmitter for a middle eastern operator. It worked at 12GHz and covered to the horizon in all directions with a power of only 3 watts. This was angle modulated. 1. Was this 12 Ghz a microwave uplink or what? Obviously your standard TV set isn't going to receive a 12 Ghz signal. 2. I have been told by TV engineers that the higher frequencies don't have near the coverage per watt that the low ones do. With this changeover in the US to digital the FCC is assigning new digital channels by lottery. There was a local TV station that had a VHF channel on analog and got assigned a UHF for the digital. They now are using twice the KWs and are spending twice the money on electricity running their new transmitter to get the same coverage area they had with the VHF. Can you clarify? Mike Metzger |
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Microwave Spectrum - Amplitude Modulation
"Creative Music Synth [220]" wrote in message om... Considering that most electric/electronic equipment work in the lower-frequency range (e.g. 50-60Hz), wouldn't higher frequencies be less vulnerable to static? Not at all. Normally running equipment drawing even substantial amounts of power at the 50/60 Hz is no problem at all for radio reception. But when that current gets interrupted or reconnected substatial amounts of RF energy can be generated over a very wide spectrum. This was in fact the earliest radio transmitter, sending Morse code by a spark gap. All you needed was a battery and the ignition coil from a model T Ford and you could transmit. Even X-Rays are generated this way: electrons are accelerated to high speed then suddenly decelerated. In their deceleration they have to give up their energy and it comes out as X radiation. So, you can have a space heater in your room drawing 2000 Watts with your radio next to it and never hear a thing. But the little shop across the street with the blinking neon sign (drawing maybe 50 watts) will drive you absolutely insane with the buzz buzz buzz all the time. And it will cover the entire radio spectrum you're trying to listen to. The advantage of higher frequencies is the use of FM, which has a built in circuit (called a discriminator) that rejects AM signals, and that's what most noise is. HTH Mike Metzger |
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Microwave Spectrum - Amplitude Modulation
"Creative Music Synth [220]" wrote in message om... Considering that most electric/electronic equipment work in the lower-frequency range (e.g. 50-60Hz), wouldn't higher frequencies be less vulnerable to static? Not at all. Normally running equipment drawing even substantial amounts of power at the 50/60 Hz is no problem at all for radio reception. But when that current gets interrupted or reconnected substatial amounts of RF energy can be generated over a very wide spectrum. This was in fact the earliest radio transmitter, sending Morse code by a spark gap. All you needed was a battery and the ignition coil from a model T Ford and you could transmit. Even X-Rays are generated this way: electrons are accelerated to high speed then suddenly decelerated. In their deceleration they have to give up their energy and it comes out as X radiation. So, you can have a space heater in your room drawing 2000 Watts with your radio next to it and never hear a thing. But the little shop across the street with the blinking neon sign (drawing maybe 50 watts) will drive you absolutely insane with the buzz buzz buzz all the time. And it will cover the entire radio spectrum you're trying to listen to. The advantage of higher frequencies is the use of FM, which has a built in circuit (called a discriminator) that rejects AM signals, and that's what most noise is. HTH Mike Metzger |
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Microwave Spectrum - Amplitude Modulation
"Creative Music Synth [220]" wrote in message om... Considering that most electric/electronic equipment work in the lower-frequency range (e.g. 50-60Hz), wouldn't higher frequencies be less vulnerable to static? Not at all. Normally running equipment drawing even substantial amounts of power at the 50/60 Hz is no problem at all for radio reception. But when that current gets interrupted or reconnected substatial amounts of RF energy can be generated over a very wide spectrum. This was in fact the earliest radio transmitter, sending Morse code by a spark gap. All you needed was a battery and the ignition coil from a model T Ford and you could transmit. Even X-Rays are generated this way: electrons are accelerated to high speed then suddenly decelerated. In their deceleration they have to give up their energy and it comes out as X radiation. So, you can have a space heater in your room drawing 2000 Watts with your radio next to it and never hear a thing. But the little shop across the street with the blinking neon sign (drawing maybe 50 watts) will drive you absolutely insane with the buzz buzz buzz all the time. And it will cover the entire radio spectrum you're trying to listen to. The advantage of higher frequencies is the use of FM, which has a built in circuit (called a discriminator) that rejects AM signals, and that's what most noise is. HTH Mike Metzger |
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Microwave Spectrum - Amplitude Modulation
"Creative Music Synth [220]" wrote in message om... Considering that most electric/electronic equipment work in the lower-frequency range (e.g. 50-60Hz), wouldn't higher frequencies be less vulnerable to static? Not at all. Normally running equipment drawing even substantial amounts of power at the 50/60 Hz is no problem at all for radio reception. But when that current gets interrupted or reconnected substatial amounts of RF energy can be generated over a very wide spectrum. This was in fact the earliest radio transmitter, sending Morse code by a spark gap. All you needed was a battery and the ignition coil from a model T Ford and you could transmit. Even X-Rays are generated this way: electrons are accelerated to high speed then suddenly decelerated. In their deceleration they have to give up their energy and it comes out as X radiation. So, you can have a space heater in your room drawing 2000 Watts with your radio next to it and never hear a thing. But the little shop across the street with the blinking neon sign (drawing maybe 50 watts) will drive you absolutely insane with the buzz buzz buzz all the time. And it will cover the entire radio spectrum you're trying to listen to. The advantage of higher frequencies is the use of FM, which has a built in circuit (called a discriminator) that rejects AM signals, and that's what most noise is. HTH Mike Metzger |
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Microwave Spectrum - Amplitude Modulation
On Sun, 22 Feb 2004 01:20:49 GMT, "Mike Metzger"
wrote: Hey Don, now *I'm* curious. I designed a TV transmitter for a middle eastern operator. It worked at 12GHz and covered to the horizon in all directions with a power of only 3 watts. This was angle modulated. 1. Was this 12 Ghz a microwave uplink or what? Obviously your standard TV set isn't going to receive a 12 Ghz signal. No, this was the broadcast link, and it was received by the customers with an analogue satellite box and special dish and LNB. 2. I have been told by TV engineers that the higher frequencies don't have near the coverage per watt that the low ones do. With this changeover in the US to digital the FCC is assigning new digital channels by lottery. There was a local TV station that had a VHF channel on analog and got assigned a UHF for the digital. They now are using twice the KWs and are spending twice the money on electricity running their new transmitter to get the same coverage area they had with the VHF. Can you clarify? Mike Metzger Although coverage per watt is not really an issue, the problem comes with no line-of-sight coverage, particularly beyond the horizon. As you go higher in frequency you need more power to penetrate shadow areas. Certainly in cities that means really high frequencies need a lot of power. Satellite TV works because the elevation of the satellite is so high that just about anybody can get line-of-sight from somewhere on their house. d _____________________________ http://www.pearce.uk.com |
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Microwave Spectrum - Amplitude Modulation
On Sun, 22 Feb 2004 01:20:49 GMT, "Mike Metzger"
wrote: Hey Don, now *I'm* curious. I designed a TV transmitter for a middle eastern operator. It worked at 12GHz and covered to the horizon in all directions with a power of only 3 watts. This was angle modulated. 1. Was this 12 Ghz a microwave uplink or what? Obviously your standard TV set isn't going to receive a 12 Ghz signal. No, this was the broadcast link, and it was received by the customers with an analogue satellite box and special dish and LNB. 2. I have been told by TV engineers that the higher frequencies don't have near the coverage per watt that the low ones do. With this changeover in the US to digital the FCC is assigning new digital channels by lottery. There was a local TV station that had a VHF channel on analog and got assigned a UHF for the digital. They now are using twice the KWs and are spending twice the money on electricity running their new transmitter to get the same coverage area they had with the VHF. Can you clarify? Mike Metzger Although coverage per watt is not really an issue, the problem comes with no line-of-sight coverage, particularly beyond the horizon. As you go higher in frequency you need more power to penetrate shadow areas. Certainly in cities that means really high frequencies need a lot of power. Satellite TV works because the elevation of the satellite is so high that just about anybody can get line-of-sight from somewhere on their house. d _____________________________ http://www.pearce.uk.com |
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Microwave Spectrum - Amplitude Modulation
On Sun, 22 Feb 2004 01:20:49 GMT, "Mike Metzger"
wrote: Hey Don, now *I'm* curious. I designed a TV transmitter for a middle eastern operator. It worked at 12GHz and covered to the horizon in all directions with a power of only 3 watts. This was angle modulated. 1. Was this 12 Ghz a microwave uplink or what? Obviously your standard TV set isn't going to receive a 12 Ghz signal. No, this was the broadcast link, and it was received by the customers with an analogue satellite box and special dish and LNB. 2. I have been told by TV engineers that the higher frequencies don't have near the coverage per watt that the low ones do. With this changeover in the US to digital the FCC is assigning new digital channels by lottery. There was a local TV station that had a VHF channel on analog and got assigned a UHF for the digital. They now are using twice the KWs and are spending twice the money on electricity running their new transmitter to get the same coverage area they had with the VHF. Can you clarify? Mike Metzger Although coverage per watt is not really an issue, the problem comes with no line-of-sight coverage, particularly beyond the horizon. As you go higher in frequency you need more power to penetrate shadow areas. Certainly in cities that means really high frequencies need a lot of power. Satellite TV works because the elevation of the satellite is so high that just about anybody can get line-of-sight from somewhere on their house. d _____________________________ http://www.pearce.uk.com |
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Microwave Spectrum - Amplitude Modulation
On Sun, 22 Feb 2004 01:20:49 GMT, "Mike Metzger"
wrote: Hey Don, now *I'm* curious. I designed a TV transmitter for a middle eastern operator. It worked at 12GHz and covered to the horizon in all directions with a power of only 3 watts. This was angle modulated. 1. Was this 12 Ghz a microwave uplink or what? Obviously your standard TV set isn't going to receive a 12 Ghz signal. No, this was the broadcast link, and it was received by the customers with an analogue satellite box and special dish and LNB. 2. I have been told by TV engineers that the higher frequencies don't have near the coverage per watt that the low ones do. With this changeover in the US to digital the FCC is assigning new digital channels by lottery. There was a local TV station that had a VHF channel on analog and got assigned a UHF for the digital. They now are using twice the KWs and are spending twice the money on electricity running their new transmitter to get the same coverage area they had with the VHF. Can you clarify? Mike Metzger Although coverage per watt is not really an issue, the problem comes with no line-of-sight coverage, particularly beyond the horizon. As you go higher in frequency you need more power to penetrate shadow areas. Certainly in cities that means really high frequencies need a lot of power. Satellite TV works because the elevation of the satellite is so high that just about anybody can get line-of-sight from somewhere on their house. d _____________________________ http://www.pearce.uk.com |
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Microwave Spectrum - Amplitude Modulation
Don Pearce schrieb:
2. I have been told by TV engineers that the higher frequencies don't have near the coverage per watt that the low ones do. With this changeover in the US to digital the FCC is assigning new digital channels by lottery. There was a local TV station that had a VHF channel on analog and got assigned a UHF for the digital. They now are using twice the KWs and are spending twice the money on electricity running their new transmitter to get the same coverage area they had with the VHF. Can you clarify? Mike Metzger Although coverage per watt is not really an issue, the problem comes with no line-of-sight coverage, particularly beyond the horizon. As you go higher in frequency you need more power to penetrate shadow areas. Certainly in cities that means really high frequencies need a lot of power. Satellite TV works because the elevation of the satellite is so high that just about anybody can get line-of-sight from somewhere on their house. the issue are not shadow aereas, that is a question of the satellites transmitantenna beamwith. The problem is caused by the higher siganlpath attenuation which raises with the frequency. Beside, attenuation on dustparticles over big cities, reindrops, fog etc. is higher on higher frequencies regards Peter |
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Microwave Spectrum - Amplitude Modulation
Don Pearce schrieb:
2. I have been told by TV engineers that the higher frequencies don't have near the coverage per watt that the low ones do. With this changeover in the US to digital the FCC is assigning new digital channels by lottery. There was a local TV station that had a VHF channel on analog and got assigned a UHF for the digital. They now are using twice the KWs and are spending twice the money on electricity running their new transmitter to get the same coverage area they had with the VHF. Can you clarify? Mike Metzger Although coverage per watt is not really an issue, the problem comes with no line-of-sight coverage, particularly beyond the horizon. As you go higher in frequency you need more power to penetrate shadow areas. Certainly in cities that means really high frequencies need a lot of power. Satellite TV works because the elevation of the satellite is so high that just about anybody can get line-of-sight from somewhere on their house. the issue are not shadow aereas, that is a question of the satellites transmitantenna beamwith. The problem is caused by the higher siganlpath attenuation which raises with the frequency. Beside, attenuation on dustparticles over big cities, reindrops, fog etc. is higher on higher frequencies regards Peter |
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Microwave Spectrum - Amplitude Modulation
Don Pearce schrieb:
2. I have been told by TV engineers that the higher frequencies don't have near the coverage per watt that the low ones do. With this changeover in the US to digital the FCC is assigning new digital channels by lottery. There was a local TV station that had a VHF channel on analog and got assigned a UHF for the digital. They now are using twice the KWs and are spending twice the money on electricity running their new transmitter to get the same coverage area they had with the VHF. Can you clarify? Mike Metzger Although coverage per watt is not really an issue, the problem comes with no line-of-sight coverage, particularly beyond the horizon. As you go higher in frequency you need more power to penetrate shadow areas. Certainly in cities that means really high frequencies need a lot of power. Satellite TV works because the elevation of the satellite is so high that just about anybody can get line-of-sight from somewhere on their house. the issue are not shadow aereas, that is a question of the satellites transmitantenna beamwith. The problem is caused by the higher siganlpath attenuation which raises with the frequency. Beside, attenuation on dustparticles over big cities, reindrops, fog etc. is higher on higher frequencies regards Peter |