Home |
Search |
Today's Posts |
|
#1
![]() |
|||
|
|||
![]()
Too many people are preoccupied with RF power; i.e, WATTS. What they don't
realize is that the MODE of operation is far more important than power... 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 is usually somewhere around 30%, so the average RF power that is transmitted is closer to 4.6 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 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! 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 about 30%. So using voice on SSB the average power will be about 4 watts. Now since we already know that SSB modulated with normal speech is 15 times more efficient than AM. Therefore, 4 watts of SSB is equivalent to 60 watts of AM power, or 52 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 half the bandwidth of AM (6 KHz for AM vs 3 KHz for SSB). That means it receives half the noise of AM, thereby doubling the all-important signal-to-noise ratio, and effectively doubling the power of the transmitted signal. All summed up, a stock CB with SSB has the same range and talk-power as the same CB using AM with a 100 watt linear -- and it's LEGAL! -----= 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! =----- |
#2
![]() |
|||
|
|||
![]()
Frank Gilliland wrote:
All summed up, a stock CB with SSB has the same range and talk-power as the same CB using AM with a 100 watt linear -- and it's LEGAL! True. -- GO# 40 ------------------------------------------------------------- http://NewsReader.Com/ 50 GB/Month |
#4
![]() |
|||
|
|||
![]()
jim wrote:
wrote: Frank Gilliland wrote: All summed up, a stock CB with SSB has the same range and talk-power as the same CB using AM with a 100 watt linear -- and it's LEGAL! True. as the brits would say, its the twig that matters..... Yea, I hear you dominate those Limey groups..hehe -- GO# 40 & Twistedhed ------------------------------------------------------------- http://NewsReader.Com/ 50 GB/Month |
#6
![]() |
|||
|
|||
![]() 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. |
#7
![]() |
|||
|
|||
![]() |
#8
![]() |
|||
|
|||
![]() 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. |
#9
![]() |
|||
|
|||
![]() "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. |
Reply |
|
Thread Tools | Search this Thread |
Display Modes | |
|
|
![]() |
||||
Thread | Forum | |||
FCC: Broadband Power Line Systems | Policy | |||
Wanted: Power Supply for TR-4C | Boatanchors | |||
Wanted: Power Supply for TR-4C | Equipment | |||
Wanted: Power Supply for TR-4C | Homebrew | |||
Wanted: Power Supply for TR-4C | Equipment |