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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. |
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