[TenTec] AM, was "Just noticed ..."

[Ken Brown]

Joel,

Yes I see what you mean. Using the same amount of power in the remaining 
sideband as was in that sideband before would result in the same SNR. I 
wonder about doubling the power in one sideband and eliminating the 
other. Same total amount of sideband power, just not two sidebands. 
Would the same carrier level be sufficient for demodulation? It may be 
that with DSB the two opposite sideband's power peaks occur in opposite 
phases of the modulating audio, not simultaneously. If all that power 
were put into a single sideband the total instantaneous peak power level 
in that one sideband would be twice what you had with DSB, requiring 
twice as much carrier for proper demodulation. Someone better versed in 
the mathematics of modulation could clarify this.

DE N6KB

joel hallas wrote:
> Ken,
>
> I guess it depends on what you assume about the way the signal power is 
> generated. You assume that the sideband power will be twice as high as 
> the power in each sideband of a DSB-AM signal. I assumed that the signal 
> power in the remaining sideband would be the same as it was in the 
> DSB-AM case, that is that the DSB-AM signal was generated at 100% 
> modulation and then one sideband was loped off by the filter. Thus the 
> noise power (by going from 6 kHz to 3 kHz BW) and signal (sideband) 
> power are both cut in half so the SNR remains the same.
>
> I guess if the transmitter were peak power limited, you could increase 
> the remaining sideband power by a factor of two and keep the same 
> carrier, but I suspect that the receiver would have some problems 
> demodulating without distortion.
>
> Regards, Joel
>
>
>   
>