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#1




AM vs. SSB technical question
In short, how does a 5watt CB produce 12W PEP in the SSB mode?
Once the carrier and one sideband are filtered out of the signal to produce a SSB signal, and this is fed to the CB's RF amplifier (which would generate 45W of AM), why wouldn't the result just be 45W of SSB? It is often described as the power being focused into one sideband, and the increased bandwidth efficiency is clear, but: if the power input to the final amplifier is the same as with AM, where do the "extra watts" come from? Or is the amplification somehow applied in a different way to the SSB signal? Not sure how to conceptualize this. Thanks! 
#2




AM vs. SSB technical question
JWG wrote:
In short, how does a 5watt CB produce 12W PEP in the SSB mode? Once the carrier and one sideband are filtered out of the signal to produce a SSB signal, and this is fed to the CB's RF amplifier (which would generate 45W of AM), why wouldn't the result just be 45W of SSB? It is often described as the power being focused into one sideband, and the increased bandwidth efficiency is clear, but: if the power input to the final amplifier is the same as with AM, where do the "extra watts" come from? Or is the amplification somehow applied in a different way to the SSB signal? Not sure how to conceptualize this. Thanks! A 4 watt AM signal sends out 4 watts when there is no modulation (A0) To fully modulate an AM signal to 100%, you mix 50% more to it, in this case, your audio. This creates 2 identical mirror image sidebands, each being 1 watt. Added together, this would show 6 watts on an RMS (average) reading meter. Ohms law being what it is, and power being related to ohms law, when you increase the voltage 50% to a fixed resistance (your antenna), the current also increases by 50%, and now your PEAK TO PEAK power is now 16 watts. The allowed increase from 4 to 12 comes from the fact that the FCC allows the power of the selected sideband to be the amount of peak power that 80% AM modulation would put out. That is part of the increase. The other part of the increase is that the receiver is more sensitive when it only has to listen to half the bandwidth of an AM signal. All told, sideband is a much more efficient use of power and radio spectrum. 
#3




Quote:
If we could see one individual radio wave, we would be able to draw a line ( carrier ) though the center and the upper side band ( the radio wave above the carrier ) would be above the carrier and the lower side band ( the radio wave below the carrier ) would be below the carrier. When we subtract one of the carriers, the forward power is transferred into the other band. Now the carrier is a power hog and probably wastes 60% of the transmitted power. So at that rate  if both side bands combined had 5 watts and you removed one of the side bands  you would effectively double the transmit power. However, you have to account for losses, the loss of the connectors, the loss in the coax, the values of all the components in the radio, to be conservative lets say it is 12 watts PEP when it is new. PEP stands for Peak Envelope Power. http://en.wikipedia.org/wiki/Peak_envelope_power The PEP output of an AM transmitter at full modulation is four times its carrier PEP; in other words, a soldstate, 100watt amateur transceiver is usually rated for no more than 25 watts carrier output when operating in AM When you turn on a vac cleaner, at the initial start up, you have a power spike which is needed to start the motor turning, that can be considered a peak power level. When manufactures sells a vac cleaner, they include the PEP power level to make the motor seem more impressive. On the other hand, a VOM meter reads Root Mean Square  RMS power. http://en.wikipedia.org/wiki/Root_mean_square Because of their usefulness in carrying out power calculations, listed voltages for power outlets, e.g. 120 V (USA) or 230 V (Europe), are almost always quoted in RMS values, and not peak values. Peak values can be calculated from RMS values from the above formula, which implies Vp = VRMS × √2, assuming the source is a pure sine wave. Thus the peak value of the mains voltage in the USA is about 120 × √2, or about 170 volts. The peaktopeak voltage, being twice this, is about 340 volts. A similar calculation indicates that the peaktopeak mains voltage in Europe is about 650 volts. It is also possible to calculate the RMS power of a signal. By analogy with RMS voltage and RMS current, RMS power is the square root of the mean of the square of the power over some specified time period. This quantity, which would be expressed in units of watts (RMS), has no physical significance. However, the term "RMS power" is sometimes used in the audio industry as a synonym for "mean power" or "average power". 
#4




AM vs. SSB technical question
THANKS Scott and Channel Jumper, I really appreciate the clear and
thoughtful replies. Extremely helpful! What I could find in texts and online has either been too technical or just glosses over this without stating "why" the increased wattage level is achieved on SSB. JG 
#5




You are welcome.
One thing I did not mention was the fact that since AC  alternating current  is harder to measure then DC current / so when we talk about RMS power. ( Root Mean Square ) we are talking about the amount of power necessary to produce a certain amount of heat into a resistor of a known value at X Volts DC. This type of measurement is what keeps us from mistaking one countries voltage  at the wall outlet, from another. 
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