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#1
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![]() snip Now AM works fine if you don't mind wasting power. This is because the audio is carried only in the sidebands, not the carrier. And because the two sidebands are mirror images of themselves, only one sideband is needed and the other is wasted. If we eliminate the carrier and one sideband (resulting in the mode called Single Sideband, or SSB), we are left with a 1 watt sideband that will work just as well as if we burned 6 watts to transmit two sidebands and a carrier. In other words, SSB is -AT LEAST- 6 times more efficient than AM. But remember that average modulation is more like 30%, which means that a 0.3 watt SSB transmission has the same effect as using 4.6 watts to transmit that very same sideband using AM. Therefore, with normal speech, SSB is closer to 15 times more efficient! snip You are wrong about SSB being 15 times more efficient. Your reasoning is flawed in that.............................................. ...... If speech modulates a AM signal to a average of 30% then the same speech will modulate a SSB to a similar reduced potential. ********************************** On A.M. , with a 4 watt carrier at 100% modulation , we have 2 watts of audio power used for the sidebands. One watt on each sideband. This duplication of sidebands is not necessary to convey intelligence. If we use the same transmitter and convert it to DSB ( double sideband ) by removing the carrier , we can now have 2 watts per sideband. If we now remove the other sideband , and concentrate all of the power into one sideband , we have a 4 watt sideband. With this method of removing the carrier and one sideband we can put 4 watts of intelligence out on SSB as compared to 1 watt on A.M.. This makes a SSB transmission 4 times as powerful as its A.M. counterpart. In addition to the above transmitting advantage , the SSB signal has a receive advantage also. Since only one sideband is transmitted , only 1/2 the bandwidth is needed. This means that twice the number of stations could operate in the same bandspace as A.M.. In addition to this , because the bandwidth needed is only 1/2 of A.M. , only 1/2 of the atmospheric noise is picked up with the signal. This gives you a 3db advantage over an A.M. receiver. So when you add it all up you have 6db gain on transmit , and 3db gain on receive. That's effectively 9db of total gain. |
#2
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#3
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![]() wrote in message ... snip Now AM works fine if you don't mind wasting power. This is because the audio is carried only in the sidebands, not the carrier. And because the two sidebands are mirror images of themselves, only one sideband is needed and the other is wasted. If we eliminate the carrier and one sideband (resulting in the mode called Single Sideband, or SSB), we are left with a 1 watt sideband that will work just as well as if we burned 6 watts to transmit two sidebands and a carrier. In other words, SSB is -AT LEAST- 6 times more efficient than AM. But remember that average modulation is more like 30%, which means that a 0.3 watt SSB transmission has the same effect as using 4.6 watts to transmit that very same sideband using AM. Therefore, with normal speech, SSB is closer to 15 times more efficient! snip You are wrong about SSB being 15 times more efficient. Your reasoning is flawed in that.............................................. ...... If speech modulates a AM signal to a average of 30% then the same speech will modulate a SSB to a similar reduced potential. ********************************** On A.M. , with a 4 watt carrier at 100% modulation , we have 2 watts of audio power used for the sidebands. One watt on each sideband. This duplication of sidebands is not necessary to convey intelligence. If we use the same transmitter and convert it to DSB ( double sideband ) by removing the carrier , we can now have 2 watts per sideband. If we now remove the other sideband , and concentrate all of the power into one sideband , we have a 4 watt sideband. With this method of removing the carrier and one sideband we can put 4 watts of intelligence out on SSB as compared to 1 watt on A.M.. This makes a SSB transmission 4 times as powerful as its A.M. counterpart. In addition to the above transmitting advantage , the SSB signal has a receive advantage also. Since only one sideband is transmitted , only 1/2 the bandwidth is needed. This means that twice the number of stations could operate in the same bandspace as A.M.. In addition to this , because the bandwidth needed is only 1/2 of A.M. , only 1/2 of the atmospheric noise is picked up with the signal. This gives you a 3db advantage over an A.M. receiver. So when you add it all up you have 6db gain on transmit , and 3db gain on receive. That's effectively 9db of total gain. While I can disagree with Frank when he's being a troll, even though is exact figures are a little off, basically he's correct. Landshark -- The happy people are those who are producing something; the bored people are those who are consuming much and producing nothing. |
#4
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![]() "Landshark" . wrote in message ... wrote in message ... snip Now AM works fine if you don't mind wasting power. This is because the audio is carried only in the sidebands, not the carrier. And because the two sidebands are mirror images of themselves, only one sideband is needed and the other is wasted. If we eliminate the carrier and one sideband (resulting in the mode called Single Sideband, or SSB), we are left with a 1 watt sideband that will work just as well as if we burned 6 watts to transmit two sidebands and a carrier. In other words, SSB is -AT LEAST- 6 times more efficient than AM. But remember that average modulation is more like 30%, which means that a 0.3 watt SSB transmission has the same effect as using 4.6 watts to transmit that very same sideband using AM. Therefore, with normal speech, SSB is closer to 15 times more efficient! snip You are wrong about SSB being 15 times more efficient. Your reasoning is flawed in that.............................................. ...... If speech modulates a AM signal to a average of 30% then the same speech will modulate a SSB to a similar reduced potential. ********************************** On A.M. , with a 4 watt carrier at 100% modulation , we have 2 watts of audio power used for the sidebands. One watt on each sideband. This duplication of sidebands is not necessary to convey intelligence. If we use the same transmitter and convert it to DSB ( double sideband ) by removing the carrier , we can now have 2 watts per sideband. If we now remove the other sideband , and concentrate all of the power into one sideband , we have a 4 watt sideband. With this method of removing the carrier and one sideband we can put 4 watts of intelligence out on SSB as compared to 1 watt on A.M.. This makes a SSB transmission 4 times as powerful as its A.M. counterpart. In addition to the above transmitting advantage , the SSB signal has a receive advantage also. Since only one sideband is transmitted , only 1/2 the bandwidth is needed. This means that twice the number of stations could operate in the same bandspace as A.M.. In addition to this , because the bandwidth needed is only 1/2 of A.M. , only 1/2 of the atmospheric noise is picked up with the signal. This gives you a 3db advantage over an A.M. receiver. So when you add it all up you have 6db gain on transmit , and 3db gain on receive. That's effectively 9db of total gain. While I can disagree with Frank when he's being a troll, even though is exact figures are a little off, basically he's correct. Landshark How the hell wouldyou know if he was off a little or not? you say this because tnom says he is off. You know **** about radios. |
#6
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In , "Landshark"
. wrote: snip While I can disagree with Frank when he's being a troll, even though is exact figures are a little off..... Here's a corrected version just for you, Hypocrite Landshark: =========== AM (Amplitude Modulation) is composed of three parts: The carrier, the lower sideband and the upper sideband. The carrier stays constant while the sidebands vary in power according to the modulation. When a 4 watt carrier is modulated to 100%, there will be 1 watt transmitted in each sideband, for a total of 6 watts of RF power that is being transmitted. But the voice can't modulate the carrier to 100% all the time -- speech does not have a constant amplitude. Average modulation of speech is generally accepted to be 33% (a peak-to-average ratio of 3 to 1), so under that standard the average RF power that is transmitted would be 4.67 watts. Now AM works fine if you don't mind wasting power. This is because the audio is carried only in the sidebands, not the carrier. And because the two sidebands are mirror images of themselves, only one sideband is needed and the other is wasted. If we eliminate the carrier and one sideband (resulting in the mode called Single Sideband, or SSB), we are left with a 1 watt sideband that will work just as well as if we burned 6 watts to transmit two sidebands and a carrier. In other words, SSB is -AT LEAST- 6 times more efficient than AM. But remember that average modulation is 33%, which means that a 0.33 watt SSB transmission has the same effect as using 4.67 watts to transmit that very same sideband using AM. Therefore, with normal speech, SSB is 14.15 times more efficient! Let's translate all this into watts. CB permits 12 watts for SSB. For speech communication, the average power is the same as the average modulation, or 33%. So using voice on SSB the average power will be 4 watts. Now since we already know that SSB modulated with normal speech is 14.15 times more efficient than AM. Therefore, 4 watts of SSB is equivalent to 56.61 watts of AM power, or 48.61 watts of carrier power with 4 watts in each sideband. And under 100% modulation the SSB power will be 12 watts, while it takes 72 watts to do the same job on AM (48 watts of carrier with 12 watts in each sideband). But SSB has another advantage: Because it only uses one sideband, it uses less than half the bandwidth of AM (6 KHz for AM vs 2.7 KHz for SSB). That means it receives 45% less noise than AM, thereby increasing the effective transmitted power by a factor of 2.22. All summed up, a CB radio capable of 12 watts PEP on SSB has the same range and talk-power as AM from an amplifier capable of 426.24 watts PEP (12 watts PEP is the power of one sideband from a 100% modulated AM signal with a carrier power of 48 watts RMS: Therefore, 48 watts RMS x 2.22 = 106.56 watts RMS (effective); 106.56 watts RMS x 4 = 426.24 watts PEP) -- and it's LEGAL! ================== Feel better? -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 80,000 Newsgroups - 16 Different Servers! =----- |
#7
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#8
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In , Swan Radioman
wrote: On Wed, 16 Jul 2003 22:08:34 -0400, wrote: snip Now AM works fine if you don't mind wasting power. This is because the audio is carried only in the sidebands, not the carrier. And because the two sidebands are mirror images of themselves, only one sideband is needed and the other is wasted. If we eliminate the carrier and one sideband (resulting in the mode called Single Sideband, or SSB), we are left with a 1 watt sideband that will work just as well as if we burned 6 watts to transmit two sidebands and a carrier. In other words, SSB is -AT LEAST- 6 times more efficient than AM. But remember that average modulation is more like 30%, which means that a 0.3 watt SSB transmission has the same effect as using 4.6 watts to transmit that very same sideband using AM. Therefore, with normal speech, SSB is closer to 15 times more efficient! snip You are wrong about SSB being 15 times more efficient. Your reasoning is flawed in that.............................................. ...... If speech modulates a AM signal to a average of 30% then the same speech will modulate a SSB to a similar reduced potential. The efficiency of SSB over AM increases as the modulation decreases, approaching infinity as the modulation and output approach zero. That's because even when there is 0% modulation in AM you still have carrier power. ********************************** On A.M. , with a 4 watt carrier at 100% modulation , we have 2 watts of audio power used for the sidebands. One watt on each sideband. This duplication of sidebands is not necessary to convey intelligence. If we use the same transmitter and convert it to DSB ( double sideband ) by removing the carrier , we can now have 2 watts per sideband. If we now remove the other sideband , and concentrate all of the power into one sideband , we have a 4 watt sideband. With this method of removing the carrier and one sideband we can put 4 watts of intelligence out on SSB as compared to 1 watt on A.M.. This makes a SSB transmission 4 times as powerful as its A.M. counterpart. You bring up an interesting point, even though you don't know what you are talking about. If the final is capable of 4 watts AM (or 16 watts PEP) then it's capable of 16 watts PEP, whether it's AM, DSB or SSB. That's assuming the final is linear, of course. If the final is Class C then you can't do SSB at all. In addition to the above transmitting advantage , the SSB signal has a receive advantage also. Since only one sideband is transmitted , only 1/2 the bandwidth is needed. This means that twice the number of stations could operate in the same bandspace as A.M.. In addition to this , because the bandwidth needed is only 1/2 of A.M. , only 1/2 of the atmospheric noise is picked up with the signal. This gives you a 3db advantage over an A.M. receiver. I said that already. So when you add it all up you have 6db gain on transmit , and 3db gain on receive. That's effectively 9db of total gain. Using a 100 watt AM transmitter SSB effective power= 1/2 of 25 watts in Each sideband, =12.5 watts 10*log 100/12.5 = 9.03 db -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 80,000 Newsgroups - 16 Different Servers! =----- |
#9
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![]() If speech modulates a AM signal to a average of 30% then the same speech will modulate a SSB to a similar reduced potential. The efficiency of SSB over AM increases as the modulation decreases, approaching infinity as the modulation and output approach zero. That's because even when there is 0% modulation in AM you still have carrier power. I stand corrected when running a mode below its maximum capability, but if you are horse racing with the transmitters power rating being equal between modes then this massive advantage disappears. This would occur in a hors race, and when it does a SSB transmission only has a 6db advantage over AM |
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