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Power vs Mode (The fundamentals)
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! =----- |
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 |
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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 |
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. |
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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. |
"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. |
In , Swan Radioman
wrote: snip Frank; Statistical studies of the distribution of signals on the air versus the signal strength shows that the probability of successful communication will be the same if the SSB power is equal to one-half the power of one of the two AM sidebands. That's exactly what I said. Your 100 watt figure is pretty close to what the studies show. Whats the Peak Envelope Power of a Legal AM radio? Where did I say anything about PEP? I know what you are trolling for (if you're not trolling then somebody else will), and yes, the PEP of a 4 watt AM carrier that is 100% modulated is 16 watts. But that number is misleading because you are forgetting that an AM signal has a lot of excess baggage. This is one instance where less is more.... PEP is used when determining the maximum power handling capability of the final (output) amplifier. In other words, if the AM carrier is going to be 4 watts, the final must be capable of providing 16 watts. It means nearly the same with SSB, because the PEP rating of the output amplifier is the peak power level at which the signal will begin to distort, and since the peak-to-average modulation ratio is about 3 to 1, a transmitter capable of 12 watts should safely handle about 4 watts average power in SSB. But if a transmitter is capable of 16 watts, it seems foolish to use AM with it's 1 watt sidebands when you can transmit SSB with an effective power of almost 200 watts AM or better, depending on your average modulation. The FCC limits the radios to 12 watts PEP, but that's still much better than 16 watts PEP in AM. In other words, PEP does not represent "talk-power". For those who don't already know, Peak Envelope Power (PEP) is the RF power at the brief instant an audio cycle peaks the modulation. PEP is used to describe SSB power because the standard wattmeter can't measure the average power of an SSB signal. For example, if your radio is capable of 12 watts PEP, your average power will be somewhere around 4 watts, but you won't be able to tell because your wattmeter will be bouncing around with your modulation. So SSB is measured with a 'peak' value (PEP) instead of a 'real' value (RMS). So even though the needle is bouncing around, you just need to keep it below the maximum PEP rating of the radio. OTOH, AM power is measured in RMS (true) watts, and is a measurement of carrier power only. The modulation is detected (demodulated) and measured seperately as a percentage. Modulation -must- be measured seperate from the carrier because carrier power should remain steady while under modulation; and modulation is read directly so the operator doesn't have to perform carrier subtractions and square-root calculations on a PEP reading in order to find the modulation percentage. Of course you can always add a PEP meter if you really want, but what's the point of making things difficult and expensive when you already have all the information you need? Why is 12 watts the limit for a legal SSB radio? Because the FCC says so. -----= 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! =----- |
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! =----- |
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! =----- |
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 |
On Wed, 16 Jul 2003 20:58:17 -0700, Frank Gilliland
wrote: In , Swan Radioman wrote: snip Frank; Statistical studies of the distribution of signals on the air versus the signal strength shows that the probability of successful communication will be the same if the SSB power is equal to one-half the power of one of the two AM sidebands. That's exactly what I said. Your 100 watt figure is pretty close to what the studies show. Whats the Peak Envelope Power of a Legal AM radio? Where did I say anything about PEP? I know what you are trolling for (if you're not trolling then somebody else will), and yes, the PEP of a 4 watt AM carrier that is 100% modulated is 16 watts. But that number is misleading because you are forgetting that an AM signal has a lot of excess baggage. This is one instance where less is more.... PEP is used when determining the maximum power handling capability of the final (output) amplifier. In other words, if the AM carrier is going to be 4 watts, the final must be capable of providing 16 watts. It means nearly the same with SSB, because the PEP rating of the output amplifier is the peak power level at which the signal will begin to distort, and since the peak-to-average modulation ratio is about 3 to 1, a transmitter capable of 12 watts should safely handle about 4 watts average power in SSB. But if a transmitter is capable of 16 watts, it seems foolish to use AM with it's 1 watt sidebands when you can transmit SSB with an effective power of almost 200 watts AM or better, depending on your average modulation. The FCC limits the radios to 12 watts PEP, but that's still much better than 16 watts PEP in AM. In other words, PEP does not represent "talk-power". For those who don't already know, Peak Envelope Power (PEP) is the RF power at the brief instant an audio cycle peaks the modulation. PEP is used to describe SSB power because the standard wattmeter can't measure the average power of an SSB signal. For example, if your radio is capable of 12 watts PEP, your average power will be somewhere around 4 watts, but you won't be able to tell because your wattmeter will be bouncing around with your modulation. So SSB is measured with a 'peak' value (PEP) instead of a 'real' value (RMS). So even though the needle is bouncing around, you just need to keep it below the maximum PEP rating of the radio. OTOH, AM power is measured in RMS (true) watts, and is a measurement of carrier power only. The modulation is detected (demodulated) and measured seperately as a percentage. Modulation -must- be measured seperate from the carrier because carrier power should remain steady while under modulation; and modulation is read directly so the operator doesn't have to perform carrier subtractions and square-root calculations on a PEP reading in order to find the modulation percentage. Of course you can always add a PEP meter if you really want, but what's the point of making things difficult and expensive when you already have all the information you need? Why is 12 watts the limit for a legal SSB radio? Because the FCC says so. Thanks for being such an asshole, You never said anything about PEP. I figured someone else was going to bring it up so I asked. My post in now way flamed or attacked you, in fact I backed you up. Whats you damn problem? |
"Swan Radioman" wrote in message ... Thanks for being such an asshole, You never said anything about PEP. I figured someone else was going to bring it up so I asked. My post in now way flamed or attacked you, in fact I backed you up. Whats you damn problem? here is a hankie, douche bag |
On Wed, 16 Jul 2003 20:58:17 -0700, Frank Gilliland
wrote: In , Swan Radioman wrote: Why is 12 watts the limit for a legal SSB radio? Because the FCC says so. Why? |
In , Swan Radioman wrote:
snip Thanks for being such an asshole, You never said anything about PEP. I figured someone else was going to bring it up so I asked. And that's why I said, "if you're not trolling then somebody else will". My post in now way flamed or attacked you, in fact I backed you up. Whats you damn problem? The PEP question raised a point that I thought should be addressed. If you took it personally then that's your problem. -----= 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! =----- |
On Thu, 17 Jul 2003 08:58:27 -0700, Frank Gilliland
wrote: In , Swan Radioman wrote: snip Thanks for being such an asshole, You never said anything about PEP. I figured someone else was going to bring it up so I asked. And that's why I said, "if you're not trolling then somebody else will". My post in now way flamed or attacked you, in fact I backed you up. Whats you damn problem? The PEP question raised a point that I thought should be addressed. If you took it personally then that's your problem. Ok, I apologize for my response to you. |
In , Swan Radioman wrote:
On Wed, 16 Jul 2003 20:58:17 -0700, Frank Gilliland wrote: In , Swan Radioman wrote: Why is 12 watts the limit for a legal SSB radio? Because the FCC says so. Why? I can only speculate. Any CB radio capable of both AM and SSB would probably use the same final, which must be linear to allow SSB operation, and be capable of 16 watts PEP (4 watts AM, 100% mod). But the -average- power of SSB, if limited to 16 watts PEP, would be higher than that of AM with a carrier of 4 watts RMS (assuming a peak-to-average modulation ratio of 3 to 1), and could require a final with higher power dissipation. So my guess would be that the FCC adopted the lower limit of 12 watts PEP to put the average RF power of SSB -below- that of AM, therefore preventing the need for a CB design that would allow AM power greater than 4 watts carrier RMS. If you have a better explanation, please share it. -----= 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! =----- |
Swan Radioman wrote
On Wed, 16 Jul 2003 20:58:17 -0700, Frank Gilliland wrote: Swan Radioman wrote: Why is 12 watts the limit for a legal SSB radio? Because the FCC says so. Why? The short answer; to facilitate communication. To allow the greatest number of people to have equal access to the CB frequencies. If everyone decided their own power limit, high power stations would overwhelm low power stations. -Aaron- |
On Thu, 17 Jul 2003 09:58:13 -0700, Frank Gilliland
wrote: In , Swan Radioman wrote: On Wed, 16 Jul 2003 20:58:17 -0700, Frank Gilliland wrote: In , Swan Radioman wrote: Why is 12 watts the limit for a legal SSB radio? Because the FCC says so. Why? I can only speculate. Any CB radio capable of both AM and SSB would probably use the same final, which must be linear to allow SSB operation, and be capable of 16 watts PEP (4 watts AM, 100% mod). But the -average- power of SSB, if limited to 16 watts PEP, would be higher than that of AM with a carrier of 4 watts RMS (assuming a peak-to-average modulation ratio of 3 to 1), and could require a final with higher power dissipation. So my guess would be that the FCC adopted the lower limit of 12 watts PEP to put the average RF power of SSB -below- that of AM, therefore preventing the need for a CB design that would allow AM power greater than 4 watts carrier RMS. If you have a better explanation, please share it. The only one that I have seen is, they just took the 16 watts PEP for AM, subtracted the 4 watts for the carrier. Thats why I asked you earlier about PEP power for an AM radio. |
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: Frank Gilliland wrote:
: 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... What many of the technical heads don't realize is the simplicity of AM mode for the average joe. The average arm chair CB person doesn't want to crank a clarifier knob in SSB operation. AM remains popular for the average CB operation regardless of efficieny issues. : 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. Modulation percentage & duty cycle. In the real world, one must consider the radio service, operator and equipment. Speech processing (power mics into proper mic limiter circuits as an example) and background noise can lead to modulation percentages greater than 30%. You should qualify your statement to say something like the typical human voice might modulate an unprocessed AM CB about 20 to 30% on average. Throw in a typical power mic or some type of speech processor box (like the Heil type of of radio equipment) and that all goes out the window. [cut and paste a little bit of good theory] With 100-percent sine-wave modulation, a transmitter produces 1.5 units of RF power. The additional 0.5 unit of power is furnished by the modulator and is distributed equally between the two sidebands. This AM transmitter is compared with an SSB transmitter rated at 0.5 unit of peak-envelope power (PEP). Peak-envelope power is defined as the RMS power developed at the crest of the modulation envelope. Many of these rec radio cb technical posts fail to mention the source of the additional power which is furnished by the modulator. : Now AM works fine if you don't mind wasting power. Most people prefer to trade the "wasted power" for the simplicity of AM operation. Kind of the SUV of radio thing... just lacking the dam cell phone planted in your ear as you drive along. : 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. Lets add some more real information. When the RF signal is demodulated in the AM receiver an audio voltage develops which is equivalent to the sum of the upper- and lower-sideband voltages, in this case 1 unit of voltage. This voltage represents the output from a diode detector as normally used for AM reception. Such detection is called coherent detection because the voltages of the two sidebands are added in the detector. When the RF signal is demodulated in the SSB receiver, an audio voltage of 0.7 unit develops which is equivalent to the transmitted upper-sideband signal. If a broadband noise level is chosen as 0.1 unit of voltage per 6 kc bandwidth, the AM bandwidth, the same noise level is equal to 0.07 unit of voltage per 3 kc bandwidth, the SSB bandwidth. These values represent the same noise power level per kc of bandwidth, that is, 0.12 divided by 6 is equal to 0.072 divided by 3. The s/n ratio for the AM system is 20 log s/n in terms of voltage, or 20 dB. For the SSB system the s/n ratio is also 20 dB. Therefore the 0.5 power unit of rated PEP for the SSB transmitter produces the same signal intelligibility as the 1 power unit of rated carrier power for the AM transmitter . In summary it can be stated that, under ideal propagating conditions but in the presence of broadband noise, an SSB signal and an AM signal provide equal s/n ratios at the receiver if the total sideband power contained in each of the signals is equal. This means that, to perform under these conditions as well as an SSB transmitter of given PEP rating, an AM transmitter requires twice that figure in carrier power rating. : 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! I don't agree, but you be your own judge. Also those of you nit pick types notice the mention just above "stock CB". It's a big deal when assuming modulation percentages and duty cycle. Throw a typical power mic into the mix and the big picture quickly changes. Many CB'ers use power mics, most AM (and FM) Broadcasters use heavy Audio processing. A science unto itself which is also an it's own industry. Your results will probably vary... cheers skipp http://sonic.ucdavis.edu |
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In , Swan Radioman
wrote: On Thu, 17 Jul 2003 08:58:27 -0700, Frank Gilliland wrote: In , Swan Radioman wrote: snip Thanks for being such an asshole, You never said anything about PEP. I figured someone else was going to bring it up so I asked. And that's why I said, "if you're not trolling then somebody else will". My post in now way flamed or attacked you, in fact I backed you up. Whats you damn problem? The PEP question raised a point that I thought should be addressed. If you took it personally then that's your problem. Ok, I apologize for my response to you. No problem. It did make me think (ouch!), and because of that I came up with the following 'quick' explanation of the difference between the CB's modes of AM and SSB: ----- The average RF power transmitted by AM is about 4.7 watts, but 4 watts are wasted in the carrier, and half of the remainder is redundant. The average RF power transmitted by SSB is about 4 watts, and wastes nothing at all. ----- Accurate? -----= 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! =----- |
In , Swan Radioman
wrote: On Thu, 17 Jul 2003 09:58:13 -0700, Frank Gilliland wrote: In , Swan Radioman wrote: On Wed, 16 Jul 2003 20:58:17 -0700, Frank Gilliland wrote: In , Swan Radioman wrote: Why is 12 watts the limit for a legal SSB radio? Because the FCC says so. Why? I can only speculate. Any CB radio capable of both AM and SSB would probably use the same final, which must be linear to allow SSB operation, and be capable of 16 watts PEP (4 watts AM, 100% mod). But the -average- power of SSB, if limited to 16 watts PEP, would be higher than that of AM with a carrier of 4 watts RMS (assuming a peak-to-average modulation ratio of 3 to 1), and could require a final with higher power dissipation. So my guess would be that the FCC adopted the lower limit of 12 watts PEP to put the average RF power of SSB -below- that of AM, therefore preventing the need for a CB design that would allow AM power greater than 4 watts carrier RMS. If you have a better explanation, please share it. The only one that I have seen is, they just took the 16 watts PEP for AM, subtracted the 4 watts for the carrier. Thats why I asked you earlier about PEP power for an AM radio. The problem here is that AM PEP is not a simple sum. For example, if you start with 16 watts PEP (100% mod) and subtract the 4 watt carrier then you are left with 12 watts that must be split between two sidebands. So each sideband should have 6 watts, but that's wrong because we already know that each sideband has only 1 watt. That is also the reason why carrier and modulation must be measured seperately with AM power -- because it's not simple addition. -----= 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! =----- |
On Thu, 17 Jul 2003 10:58:16 -0700, Frank Gilliland
wrote: In , Swan Radioman wrote: On Thu, 17 Jul 2003 09:58:13 -0700, Frank Gilliland wrote: In , Swan Radioman wrote: On Wed, 16 Jul 2003 20:58:17 -0700, Frank Gilliland wrote: In , Swan Radioman wrote: Why is 12 watts the limit for a legal SSB radio? Because the FCC says so. Why? I can only speculate. Any CB radio capable of both AM and SSB would probably use the same final, which must be linear to allow SSB operation, and be capable of 16 watts PEP (4 watts AM, 100% mod). But the -average- power of SSB, if limited to 16 watts PEP, would be higher than that of AM with a carrier of 4 watts RMS (assuming a peak-to-average modulation ratio of 3 to 1), and could require a final with higher power dissipation. So my guess would be that the FCC adopted the lower limit of 12 watts PEP to put the average RF power of SSB -below- that of AM, therefore preventing the need for a CB design that would allow AM power greater than 4 watts carrier RMS. If you have a better explanation, please share it. The only one that I have seen is, they just took the 16 watts PEP for AM, subtracted the 4 watts for the carrier. Thats why I asked you earlier about PEP power for an AM radio. The problem here is that AM PEP is not a simple sum. For example, if you start with 16 watts PEP (100% mod) and subtract the 4 watt carrier then you are left with 12 watts that must be split between two sidebands. So each sideband should have 6 watts, but that's wrong because we already know that each sideband has only 1 watt. That is also the reason why carrier and modulation must be measured seperately with AM power -- because it's not simple addition. So what do you think power output of a average legal SSB CB is? 12 Watts? |
In , Skipp peaks into this mess
wrote: : Frank Gilliland wrote: : 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... What many of the technical heads don't realize is the simplicity of AM mode for the average joe. The average arm chair CB person doesn't want to crank a clarifier knob in SSB operation. AM remains popular for the average CB operation regardless of efficieny issues. I don't think it's a matter of the adjustment of one knob, since people seem to get their kicks out of having lots of knobs on their radios. I think it's more about the cost of the radios. You can pick up an AM rig at any flea market for pennies; but a working SSB rig, new -or- used (that hasn't been butchered), will cost you a few bills. : 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. Modulation percentage & duty cycle. Duty cycle is irrelevant since there is no modulation percentage to be measured when the radio isn't transmitting. In the real world, one must consider the radio service, operator and equipment. Speech processing (power mics into proper mic limiter circuits as an example) and background noise can lead to modulation percentages greater than 30%. You should qualify your statement to say something like the typical human voice might modulate an unprocessed AM CB about 20 to 30% on average. Throw in a typical power mic or some type of speech processor box (like the Heil type of of radio equipment) and that all goes out the window. I took the peak-to-average modulation ratio from the ARRL handbook (as well as several other textbooks). Take up your argument with it's author. [cut and paste a little bit of good theory] With 100-percent sine-wave modulation, a transmitter produces 1.5 units of RF power. ....."units"? The additional 0.5 unit of power is furnished by the modulator and is distributed equally between the two sidebands. This AM transmitter is compared with an SSB transmitter rated at 0.5 unit of peak-envelope power (PEP). If the "additional 0.5 unit of power" is distributed equally between the two sidebands, don't you mean 0.25 unit for a single sideband? Peak-envelope power is defined as the RMS power developed at the crest of the modulation envelope. Many of these rec radio cb technical posts fail to mention the source of the additional power which is furnished by the modulator. I didn't. Read my post again. : Now AM works fine if you don't mind wasting power. Most people prefer to trade the "wasted power" for the simplicity of AM operation. Kind of the SUV of radio thing... just lacking the dam cell phone planted in your ear as you drive along. And I prefer to believe that "most people" are uneducated as to the benefits of SSB, which is why I wrote that post. : 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. Lets add some more real information. When the RF signal is demodulated in the AM receiver an audio voltage develops which is equivalent to the sum of the upper- and lower-sideband voltages, in this case 1 unit of voltage. This voltage represents the output from a diode detector as normally used for AM reception. Such detection is called coherent detection because the voltages of the two sidebands are added in the detector. Holy Smoked Oysters, Skip! That's called "envelope detection" and has nothing to do with sidebands! And the "coherer detector" was an ancient method of detection that was used long before tubes, even before galena crystals! It used iron filings that magnetized and 'cohered' to each other under modulated RF currents, changing the overall resistance with the modulation. You are WAY, WAY out in yonder pasture with THAT one, Skip. When the RF signal is demodulated in the SSB receiver, an audio voltage of 0.7 unit develops which is equivalent to the transmitted upper-sideband signal. If a broadband noise level is chosen as 0.1 unit of voltage per 6 kc bandwidth, the AM bandwidth, the same noise level is equal to 0.07 unit of voltage per 3 kc bandwidth, the SSB bandwidth. A bit obtuse, but ok.... These values represent the same noise power level per kc of bandwidth, Wrong. Noise voltage level is NOT noise power level, the latter being the sum of all the noise within the bandwidth. Narrowing the bandwidth does not reduce the noise voltage level but it DOES reduce the noise power level, and it does so in direct proportion to the bandwidth. IOW, cut the bandwidth in half and you cut the noise power level in half. snip faulty explanation based on your lack of understanding : 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! I don't agree, but you be your own judge. Also those of you nit pick types notice the mention just above "stock CB". It's a big deal when assuming modulation percentages and duty cycle. Throw a typical power mic into the mix and the big picture quickly changes. Many CB'ers use power mics, most AM (and FM) Broadcasters use heavy Audio processing. A science unto itself which is also an it's own industry. Overmodulation is next week's lesson. Your results will probably vary... cheers skipp http://sonic.ucdavis.edu -----= 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! =----- |
In , Swan Radioman
wrote: snip So what do you think power output of a average legal SSB CB is? 12 Watts? If you mean the average power output of a legal SSB CB, and based on a peak-to-average modulation ratio of 3 to 1, I would have to say 4 watts. -----= 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! =----- |
Hell with it all ,LETS go to the FM mode.
No BS about PEP, Just plain power, no linear amp required. No clipping of the modulation diodes and screwing up the radio. No forward swing or splatter, Oh that's right if it sounds good, and does not **** up the radio it couldn't be a CB radio. Service techs would not like it also as they would have nothing to do to except to screw them up. |
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They have done it in Europe on CB why not here.
Sounds much better, cuts most of the multi carrier wine out, and all the other services have done it since the 1940s. I guess we are stuck with the AM mode, that sucks. OK, OK I know its wider in the required bandwidth, SO. |
: Frank Gilliland wrote:
: I don't think it's a matter of the adjustment of one knob, since people : seem to get their kicks out of having lots of knobs on their radios. I : think it's more about the cost of the radios. You can pick up an AM rig : at any flea market for pennies; but a working SSB rig, new -or- used : (that hasn't been butchered), will cost you a few bills. AM vs SSB operation for the average evening arm chair talker (not living in a congested area) is probably going to be based a lot on simplicity and fidelity. The reduced bandwidth of an SSB signal is not as plesant to the ear for some people. Add that with the clarifier knob requirement of SSB round table group chat and AM remains popular. One must consider the practical part of radio operation after they've spent the money. :Modulation percentage & duty cycle. : Duty cycle is irrelevant since there is no modulation percentage to be : measured when the radio isn't transmitting. Hard to have one without the other... all the given examples were of a transmitted signal. : I took the peak-to-average modulation ratio from the ARRL handbook (as : well as several other textbooks). Take up your argument with it's author. There is no argument, but many reference values are thrown out by various texts based on many qualifiers. Said qualifiers should probably be mentioned in various examples. Older texts I've seen often throw out the 20% number. :[cut and paste a little bit of good theory] :With 100-percent sine-wave modulation, a transmitter produces 1.5 :units of RF power. : ...."units"? Yep, when no specific description is used, units work very well. Kind of like the unit circle often described in mathematics "with a radius of 1." Should be rather intuitive to most people... : The additional 0.5 unit of power is furnished by the :modulator and is distributed equally between the two sidebands. This AM :transmitter is compared with an SSB transmitter rated at 0.5 unit of :peak-envelope power (PEP). : If the "additional 0.5 unit of power" is distributed equally between the two : sidebands, don't you mean 0.25 unit for a single sideband? Same thing isn't it..? wait a minute... you used "unit" Frank... see how well that works. :-) :Many of these rec radio cb technical posts fail to mention the source of :the additional power which is furnished by the modulator. : I didn't. Read my post again. No one said you did... though as stated "many" people have. :Most people prefer to trade the "wasted power" for the simplicity of AM :operation. Kind of the SUV of radio thing... just lacking the dam cell :phone planted in your ear as you drive along. : And I prefer to believe that "most people" are uneducated as to the : benefits of SSB, which is why I wrote that post. Many people have SSB mode and prefer the simplicity of AM operation. "Life is box of chocolatte." Sometimes the technical candy is a hard chew. :When the RF signal is demodulated in the AM receiver an audio voltage :develops which is equivalent to the sum of the upper- and lower-sideband :voltages, in this case 1 unit of voltage. This voltage represents the :output from a diode detector as normally used for AM reception. Such :detection is called coherent detection because the voltages of the two :sidebands are added in the detector. : Holy Smoked Oysters, Skip! That's called "envelope detection" and has : nothing to do with sidebands! And the "coherer detector" was an ancient : method of detection : that was used long before tubes, even before galena crystals! It used iron : filings that magnetized and 'cohered' to each other under modulated RF currents, : changing the overall resistance with the modulation. You are WAY, WAY out in : yonder pasture with THAT one, Skip. For the example, compare the described coherent detection to envelope detection. In the classic example are they not similar..? :When the RF signal is demodulated in the SSB receiver, an audio voltage :of 0.7 unit develops which is equivalent to the transmitted :upper-sideband signal. If a broadband noise level is chosen as 0.1 unit :of voltage per 6 kc bandwidth, the AM bandwidth, the same noise level is :equal to 0.07 unit of voltage per 3 kc bandwidth, the SSB bandwidth. : A bit obtuse, but ok.... The actual word you should have used is "accurate." :These values represent the same noise power level per kc of bandwidth, : Wrong. Noise voltage level is NOT noise power level, the latter being the sum of : all the noise within the bandwidth. Narrowing the bandwidth does not reduce the : noise voltage level but it DOES reduce the noise power level, and it does so in : direct proportion to the bandwidth. IOW, cut the bandwidth in half and you cut : the noise power level in half. : snip faulty explanation based on your lack of understanding Convenient that you cut out the entire example... no one wrote that noise voltage is noise power... notice the word "represent" Frank. Also notice the example has values worked through to demonstrate the signal intelligibility. Are any of those values or the end result summary wrong Frank..? The desciption and the summary are accurate. How about you plugging in a similar example and going through it here on the news group. : Overmodulation is next week's lesson. Let's get this one done first... skipp http://sonic.ucdavis.edu |
In , Skipp has regular no decafe fake stuff
wrote: : Frank Gilliland wrote: : I don't think it's a matter of the adjustment of one knob, since people : seem to get their kicks out of having lots of knobs on their radios. I : think it's more about the cost of the radios. You can pick up an AM rig : at any flea market for pennies; but a working SSB rig, new -or- used : (that hasn't been butchered), will cost you a few bills. AM vs SSB operation for the average evening arm chair talker (not living in a congested area) is probably going to be based a lot on simplicity and fidelity. The reduced bandwidth of an SSB signal is not as plesant to the ear for some people. SSB has the same audio bandwidth as AM, but SSB has less noise. For fidelity, SSB has AM beat. Add that with the clarifier knob requirement of SSB round table group chat and AM remains popular. I haven't had to move my clarifier in quite a while, mainly because most of the people I talk to are using radios that haven't been modified. One must consider the practical part of radio operation after they've spent the money. :Modulation percentage & duty cycle. : Duty cycle is irrelevant since there is no modulation percentage to be : measured when the radio isn't transmitting. Hard to have one without the other... all the given examples were of a transmitted signal. Duty cycle is the ratio of transmit time to receive time. Modulation percentage doesn't use receive time as a factor. : I took the peak-to-average modulation ratio from the ARRL handbook (as : well as several other textbooks). Take up your argument with it's author. There is no argument, but many reference values are thrown out by various texts based on many qualifiers. Said qualifiers should probably be mentioned in various examples. Older texts I've seen often throw out the 20% number. Power microphones, audio processors, modulation limiters... things that change the peak-to-average modulation ratio... all will be discussed soon. :[cut and paste a little bit of good theory] :With 100-percent sine-wave modulation, a transmitter produces 1.5 :units of RF power. : ...."units"? Yep, when no specific description is used, units work very well. Kind of like the unit circle often described in mathematics "with a radius of 1." Should be rather intuitive to most people... You might have said that the carrier power is the base unit. : The additional 0.5 unit of power is furnished by the :modulator and is distributed equally between the two sidebands. This AM :transmitter is compared with an SSB transmitter rated at 0.5 unit of :peak-envelope power (PEP). : If the "additional 0.5 unit of power" is distributed equally between the two : sidebands, don't you mean 0.25 unit for a single sideband? Same thing isn't it..? That depends: what's one half of 0.5? wait a minute... you used "unit" Frank... see how well that works. :-) :Many of these rec radio cb technical posts fail to mention the source of :the additional power which is furnished by the modulator. : I didn't. Read my post again. No one said you did... though as stated "many" people have. Then how is it relevant to this discussion? :Most people prefer to trade the "wasted power" for the simplicity of AM :operation. Kind of the SUV of radio thing... just lacking the dam cell :phone planted in your ear as you drive along. : And I prefer to believe that "most people" are uneducated as to the : benefits of SSB, which is why I wrote that post. Many people have SSB mode and prefer the simplicity of AM operation. "Life is box of chocolatte." Sometimes the technical candy is a hard chew. I didn't say they are Gumps, I said they are uneducated about the benefits of SSB. And I should rephrase that: "Many CBers are UNDER-educated about the benefits of SSB." :When the RF signal is demodulated in the AM receiver an audio voltage :develops which is equivalent to the sum of the upper- and lower-sideband :voltages, in this case 1 unit of voltage. This voltage represents the :output from a diode detector as normally used for AM reception. Such :detection is called coherent detection because the voltages of the two :sidebands are added in the detector. : Holy Smoked Oysters, Skip! That's called "envelope detection" and has : nothing to do with sidebands! And the "coherer detector" was an ancient : method of detection : that was used long before tubes, even before galena crystals! It used iron : filings that magnetized and 'cohered' to each other under modulated RF currents, : changing the overall resistance with the modulation. You are WAY, WAY out in : yonder pasture with THAT one, Skip. For the example, compare the described coherent detection to envelope detection. In the classic example are they not similar..? No, they aren't similar at all, because I have never heard of a detection scheme where the "voltages of the two sidebands are added in the detector". Care to reference that one? Time for another lesson: You can look at AM in two ways. One way is in the frequency domain, with a carrier of constant amplitude and the modulation carried in the sidebands. The other way is in the amplitude domain, in which the carrier varies in amplitude according to the modulation (which is where the term "Amplitude Modulation" originated). Envelope detection works in the amplitude domain by passing the rectified RF or IF signal through a low-pass filter. And in case you didn't notice, a diode detector blocks half the modulation power! :When the RF signal is demodulated in the SSB receiver, an audio voltage :of 0.7 unit develops which is equivalent to the transmitted :upper-sideband signal. If a broadband noise level is chosen as 0.1 unit :of voltage per 6 kc bandwidth, the AM bandwidth, the same noise level is :equal to 0.07 unit of voltage per 3 kc bandwidth, the SSB bandwidth. : A bit obtuse, but ok.... The actual word you should have used is "accurate." The description is accurate in fact but not in reason. :These values represent the same noise power level per kc of bandwidth, : Wrong. Noise voltage level is NOT noise power level, the latter being the sum of : all the noise within the bandwidth. Narrowing the bandwidth does not reduce the : noise voltage level but it DOES reduce the noise power level, and it does so in : direct proportion to the bandwidth. IOW, cut the bandwidth in half and you cut : the noise power level in half. : snip faulty explanation based on your lack of understanding Convenient that you cut out the entire example... no one wrote that noise voltage is noise power... notice the word "represent" Frank. All right, if you really want: These values represent the same noise power level per kc of bandwidth, that is, 0.12 divided by 6 is equal to 0.072 divided by 3. Where did you get the values of 0.12 and 0.072? Regardless, 0.12 / 6 = 0.02 0.072 / 3 = 0.024 0.02 0.024 The s/n ratio for the AM system is 20 log s/n in terms of voltage, or 20 dB. For the SSB system the s/n ratio is also 20 dB. Again, where did you get your values of 0.12 and 0.072? Time for ANOTHER lesson: The intelligibility of an audio signal is defined by the signal-to-noise ratio of the audio, which is done by measuring the POWER of the signal and noise, NOT just their voltage. Why? Because sound requires POWER. Simple, huh? Also, when determining the S/N ratio at the RF input of a receiver, the signal and noise are measured as VOLTAGE because the input impedance is common to both. Therefore the 0.5 power unit of rated PEP for the SSB transmitter produces the same signal intelligibility as the 1 power unit of rated carrier power for the AM transmitter . Your "1 power unit of rated carrier power" doesn't carry any intelligence. But I know what you are trying to say, and you're still wrong. Your detection-adder scheme doesn't work here because, even if such a detector existed, the RF noise would be detected by the same process, negating the effect you are claiming actually occurs. In summary it can be stated that, under ideal propagating conditions but in the presence of broadband noise, ....which is a contradition in terms... an SSB signal and an AM signal provide equal s/n ratios at the receiver if the total sideband power contained in each of the signals is equal. Only with your sideband-adding detector. This means that, to perform under these conditions as well as an SSB transmitter of given PEP rating, an AM transmitter requires twice that figure in carrier power rating. Even if that were true (and it isn't), SSB is still more efficient than AM. Also notice the example has values worked through to demonstrate the signal intelligibility. Are any of those values or the end result summary wrong Frank..? Your values are not "worked through". It's like you pulled them out of thin air. Where did you get your values of 0.12 and 0.072? The desciption and the summary are accurate. How about you plugging in a similar example and going through it here on the news group. How about you learning the concepts before making invalid examples? How about assigning proper labels to your arbitrary values instead of generic "units"? How about not skipping steps to hide your mathematical mistakes? : Overmodulation is next week's lesson. Let's get this one done first... As far as I'm concerned, it's done. The only problem here is that you don't fully understand the concepts involved. Demonstrate that you have learned something and I'll move on. -----= 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! =----- |
In , Skipp
wrote: : Frank Gilliland wrote: : SSB has the same audio bandwidth as AM, but SSB has less noise. For fidelity, : SSB has AM beat. I and others would probably disagree. But to each his own. My AM bandwidth is not the same as my SSB bandwidth. For the most part, regular AM bandwidth is wider than SSB. Good grief.... The audio bandwidth (for CB) is the same -- 0.3 to 3 KHz. The RF bandwidth of AM is more than twice the witch of SSB because it covers from 3 KHz below to 3 KHz above the carrier, and therefore picks up more than twice the noise as SSB. : Add that with the clarifier knob requirement of SSB :round table group chat and AM remains popular. : I haven't had to move my clarifier in quite a while, mainly because most of the : people I talk to are using radios that haven't been modified. No two unmodified radios are on the same exact frequency. Given a group of stock radios, some will be either side of the assumed channel center. You don't need the radios to be on the -same exact- frequency, just really close. And the DEVIATION from that center frequency in an unmodified radio isn't significant as long as the radio has been properly aligned and maintained. Ever hear of a 'bell curve'? You and Tnom should get together and form a study group on that subject. And if you -really- want to pick some nits, you two should also study some things about temperature compensated crystal oscillators (TCXO's), PLL frequency synthesis using dual-modulus prescalers, the frequency response of the human ear and it's variation between different people, the psychology of sensory perception, etc. : Duty cycle is the ratio of transmit time to receive time. Modulation percentage : doesn't use receive time as a factor. It's more than than just Tx and Rx times... But receive time has NOTHING to do with modulation percentage! Is that so hard to understand? Sheesh....! : Power microphones, audio processors, modulation limiters... things that change : the peak-to-average modulation ratio... all will be discussed soon. Opinions will vary quite a bit... Opinions are like assholes -- everyone has one and they all stink. I don't plan on discussing opinions. Just facts. And when people have the -facts- they can make their -own- opinions based on the -facts- instead of relying upon the uneducated opinions of some wannabe-tech keyclowns. :: ...."units"? : :Yep, when no specific description is used, units work very well. Kind of :like the unit circle often described in mathematics "with a radius of 1." :Should be rather intuitive to most people... : You might have said that the carrier power is the base unit. But I did not... No you didn't. At least we agree on something! ::Many of these rec radio cb technical posts fail to mention the source of ::the additional power which is furnished by the modulator. :: I didn't. Read my post again. : :No one said you did... though as stated "many" people have. : Then how is it relevant to this discussion? You want to get the information out... might as well lay the proper foundation. Nice thought, but you didn't build anything on that foundation! ::Most people prefer to trade the "wasted power" for the simplicity of AM ::operation. Kind of the SUV of radio thing... just lacking the dam cell ::phone planted in your ear as you drive along. : :: And I prefer to believe that "most people" are uneducated as to the :: benefits of SSB, which is why I wrote that post. : :Many people have SSB mode and prefer the simplicity of AM operation. "Life :is box of chocolatte." Sometimes the technical candy is a hard chew. : I didn't say they are Gumps, I said they are uneducated about the benefits of : SSB. And I should rephrase that: "Many CBers are UNDER-educated about the : benefits of SSB." No one mentioned Forest Gumps... just playing devils advocate, one should compare the benefits with the trade offs. And the person that is making such a comparison should have all the facts available, such as the power and efficiency benefits of SSB over AM. Gee, we agree on something else! : No, they aren't similar at all, because I have never heard of a detection scheme : where the "voltages of the two sidebands are added in the detector". Care to : reference that one? su http://dj4br.virtualave.net/ssb3e.htm Next time you plagiarize a ham you better verify his 'facts' first -- here is a site that does an excellent job of explaining 'coherent detection': http://www.qsl.net/dj7hs/ccwtheo.htm BTW, did you notice where he talked about SSB and how the frequency of the reinserted carrier "may be in error by 100 cycles or more without serious loss of intelligibility"? That kinda puts the crimp on your "same exact frequency" complaint. : Time for another lesson: You can look at AM in two ways. One way is in the : frequency domain, with a carrier of constant amplitude and the modulation : carried in the sidebands. The other way is in the amplitude domain, in which the : carrier varies in amplitude according to the modulation (which is where the term : "Amplitude Modulation" originated). Envelope detection works in the amplitude : domain by passing the rectified RF or IF signal through a low-pass filter. And : in case you didn't notice, a diode detector blocks half the modulation power! Depends on the detector type... there are more than single diode detectors, even for AM operation. When was the last time you saw a full-wave AM detector? : All right, if you really want: :These values represent the same noise power level per kc of bandwidth, :that is, 0.12 divided by 6 is equal to 0.072 divided by 3. : Where did you get the values of 0.12 and 0.072? Regardless, : 0.12 / 6 = 0.02 : 0.072 / 3 = 0.024 : 0.02 0.024 http://dj4br.virtualave.net/ssb3e.htm God damn, Skip, how dumb can you be? You just copy the stuff without any comprehension of what it means? His figures of 0.12 and 0.072 are just typos; they are supposed to be 0.1 squared and 0.07 squared: 0.1^2 = 0.01 0.01 / 6 = 0.00167 0.07^2 = 0.0049 0.0049 / 3 = 0.00163 And they STILL aren't equal because his 'arbitrary' level of noise voltage wasn't picked arbitrarily -- it was cooked and rounded from the intended result! Didn't I suggest a long time ago that you should quit relying solely on the internet for your education? I'm pretty sure I did.... : The s/n ratio :for the AM system is 20 log s/n in terms of voltage, or 20 dB. For the :SSB system the s/n ratio is also 20 dB. : Again, where did you get your values of 0.12 and 0.072? http://dj4br.virtualave.net/ssb3e.htm : Time for ANOTHER lesson: The intelligibility of an audio signal is defined by : the signal-to-noise ratio of the audio, which is done by measuring the POWER of : the signal and noise, NOT just their voltage. Why? Because sound requires POWER. : Simple, huh? Also, when determining the S/N ratio at the RF input of a receiver, : the signal and noise are measured as VOLTAGE because the input impedance is : common to both. http://dj4br.virtualave.net/ssb3e.htm "Electronic Communication" by Shrader, McGraw-Hill "Applied Electronic Comminucation" by Kellejian, SRA http://www.epanorama.net/documents/a...oisetypes.html http://www.laidback.org/~daveg/acade...tml/comms.html http://www.isr.umd.edu/CAAR/papers/m...ysis/model.pdf Try again, Skip. : Therefore the 0.5 power unit of :rated PEP for the SSB transmitter produces the same signal :intelligibility as the 1 power unit of rated carrier power for the AM :transmitter . : Your "1 power unit of rated carrier power" doesn't carry any intelligence. But I : know what you are trying to say, and you're still wrong. Your detection-adder : scheme doesn't work here because, even if such a detector existed, the RF noise : would be detected by the same process, negating the effect you are claiming : actually occurs. http://dj4br.virtualave.net/ssb3e.htm Well, let's see... If the sidebands are added in the detector, then so is the broadband noise with each sideband. So you have twice the noise bandwidth, and therefore twice the noise power. above references, but if those are too complicated try this one: http://www.geocities.com/w4jbm/noise.html :In summary it can be stated that, under ideal propagating conditions but :in the presence of broadband noise, : ...which is a contradition in terms... http://dj4br.virtualave.net/ssb3e.htm That's right, blame it on the person you plagiarized. : an SSB signal and an AM signal provide :equal s/n ratios at the receiver if the total sideband power contained in :each of the signals is equal. : Only with your sideband-adding detector. : This means that, to perform under these :conditions as well as an SSB transmitter of given PEP rating, an AM :transmitter requires twice that figure in carrier power rating. : Even if that were true (and it isn't), SSB is still more efficient than AM. No one disputes SSB being more efficient, just less practical for the average real world CB radio operator. http://dj4br.virtualave.net/ssb3e.htm http://dj4br.virtualave.net/ssb4e.htm :Also notice the example has values worked through to demonstrate the :signal intelligibility. Are any of those values or the end result :summary wrong Frank..? : Your values are not "worked through". It's like you pulled them out of thin air. : Where did you get your values of 0.12 and 0.072? http://dj4br.virtualave.net/ssb3e.htm :The desciption and the summary are accurate. : :How about you plugging in a similar example and going through it here on :the news group. : How about you learning the concepts before making invalid examples? How about : assigning proper labels to your arbitrary values instead of generic "units"? How : about not skipping steps to hide your mathematical mistakes? http://dj4br.virtualave.net/ssb3e.htm Now you are just being lazy. :: Overmodulation is next week's lesson. : :Let's get this one done first... : As far as I'm concerned, it's done. The only problem here is that you don't : fully understand the concepts involved. Demonstrate that you have learned : something and I'll move on. http://dj4br.virtualave.net/ssb3e.htm I like the example description shown, have a look and get back to us with what ever gets your motor sideways... you might also cc the author if you have specific questions about his statements. You might do that yourself to notify him of his mistakes in both theory and mathematical notation. Then spend a few hours at your public library reading some -qualified- material on these subjects. You might start with the ARRL's "Radio Amateur's Handbook", which disagrees in every topic you have referenced from your source. -----= 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! =----- |
In , Frank is a bitter man
wrote: Frankie, It used to be a lot of fun to pull your chain, but like Michael Savage, you are now mostly a bitter mean jackass. So I'm done having a bit of fun jacking you up... Your ratings are way down... back to O'Riley on Fox. maybe next time... skipp What a cop-out! I disprove your BS, and instead of opening your mind (and a few books) to the facts, you run away with your tail between your legs and call me a "bitter mean jackass". Why? I didn't use any name-calling -- I didn't even call you 'Skippy' in this thread! But you turn and call me a "bitter mean jackass" because I point out that your technical information is seriously faulty? Well, kiss my ass, Skippy! BTW, you never did reply to my last post in our previous exchange. Remember this one? http://groups.google.com/groups?hl=e...40news.cet.com Just like the last time, you have proven that you know far less about radio than you claim. And just like the last time, you are backing away using the "I don't care" attitude. Go away, Skippy. Go try and impress your amp-gods, because you aren't impressing anyone here. -----= 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! =----- |
IP Daily, more then once, wrote: Skipp, Landshark, and a few of the other turd burglars from the group have a question for you regarding your changing of your name,nic email every post, god knows it bothers them when I do it. The difference is, Skipp gives a place for him to be contacted, not pretending he is who is he isn't. While this isn't on every post, it's on enough for a legal ID: cheers skipp http://sonic.ucdavis.edu Try clicking the link... |
I thought we had to ID every 10 minutes...
:-) s. : Scott Unit 69 wrote: : The difference is, Skipp gives a place for him to be contacted, : not pretending he is who is he isn't. : While this isn't on every post, it's on enough for a legal ID: : cheers : skipp : http://sonic.ucdavis.edu : Try clicking the link... |
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