Sunday, November 16, 2008

ATSC peak-to-average

So I may be realizing that the peak-to-average ratio of ATSC may actually be closer to 5 dB rather than 3 dB. It is true that the maximum actual amplitude sampling point is 3 dB above average, but the signal over-swings beyond that, and attempting to clip it just forces the out-of-channel sidebands up.

In these views, the reference level is actually 20 db higher than listed, because there is a 20 dB attenuator on the input to the SA.

That's the output of the amplifier at minimum driver power - which results in about 6-7 watts of channel average power output. The skits that are visible at about -25 dBm were present in the output from the exciter, but were slightly lower (maybe 5 dB) relative to the main signal.

That's the output at one notch up from the minimum - which is about 10-12 watts of average power or so, but it's a bit uglier.

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