[AMRadio] Trouble brewing ... |
Donald Chester
k4kyv at charter.net
Mon Dec 16 15:58:40 EST 2013
Bry Carling wrote: > 24KW PEP for parity? I think not. > > Bry Carling > http://af4k.com For parity in talk power, you would need the same total sideband power for both modes. 1500 watts of peak sideband power for AM translates to 3000 watts of fully modulated carrier power, since only on voice PEAKS does the modulation hit 100%. The modulating signal must be 50% of the carrier power to modulate 100%, or 1500 watts of power in the two sidebands combined at voice peaks to fully modulate the 3 kw carrier. 1500 watts of sideband power is 1500 watts of sideband power, regardless of whether all the power is concentrated into one sideband, or distributed into two sidebands. The carrier is just "there" for a reference; it neither adds nor takes away anything from the talk power With SSB, the receiver passband need be only one half as wide as with DSB, so you get a 3 dB s/n ratio advantage with SSB due to the narrower passband at the receiver, which lets in only half the random noise. That would represent a 3 dB improvement for SSB. But, with DSB, the voltages from two sidebands add vectorally, so that the peak voltage at the receiver detector from the two sidebands combined adds up to twice the peak voltage that would result from each one of the sidebands received individually. P = voltage squared X R. Doubling the voltage by vectorally combining the two sidebands gives twice the voltage or 4 times the power of each sideband taken individually, or 6 dB. But since the receiver passband allows in 3 dB more noise with DSB, the actual improvement in s/n ratio is only 3 dB. The net improvement from combining the upper and lower sidebands is 3 dB over each one of the sidebands transmitted alone, exactly what would be expected since the total sideband power of both the sidebands is twice that of each one. Don k4kyv --- This email is free from viruses and malware because avast! Antivirus protection is active. http://www.avast.com
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