Hi Al > CESSB therefore provides you an additional 4-5dB > > (typical) of distortion free gain > > 73 Hans G0UPL > > It's not quite that much, Hans. The original CESSB article was in QEX, > Nov/Dec 2014, by Dave Hershberger, W9GR. According to his calculations he > was seeing approximately 2.6 dB increase in average power for a given > peak-envelope-power. For a KX3 running 13W PEP and, say, 4W average, a 2.6 > dB increase would result in an average power of about 7.2W for the same > PEP. That's still significant. >
2.6dB is the quoted benefit compared to a state of the art, fast look-ahead ALC system. İn other words the best ALC you can get. This is on the last page of the 2014 article and right before that they mentioned the 3.8dB measurement for that particular audio sample. Most radios have a less advanced ALC function which is why 4-5dB is more typical - but it does depend a lot on the nature of the speech. Well worth noting is that during the development of CESSB for QMX/QMX+ I was able to clearly demonstrate experimentally that the more compression you add, the more dB benefit you get when you switch on CESSB. This is important because often people are using compression and without realizing that due to the SSB overshoot problem, the ALC now has to reduce the gain even more to avoid the splatter. In other words some of the dB you got by using compression, you give back because the ALC had to more aggressively reduce it due to higher envelope overshoots; but with CESSB you get to keep all the compression dB advantages (plus the regular advantage of CESSB). This is also evident by theoretical analysis: in the first few pages of the 2014 Hershberger article the Hilbert Transform of a square wave is plotted; the overshoot is a little over 9dB. A square wave audio at the bottom end of the SSB passband would have enough harmonic content to somewhat approximate pretty close to a square wave and get perhaps close to this 9dB but of course in practice this doesn't happen. Nevertheless the theoretical hounds for the CESSB "advantage" are therefore 0dB (simple waveform such as a single tone or two-tone test signal), and 9dB (unlikely square wave). Ordinary speech night be 4dB with a lower advantage relative to the best fast look-ahead ALC systems (2.6dB is quoted). But as more compression is added to the audio, it goes in the direction of square waves (not claiming that it is anything close to getting there), and this is why the dB benefit of CESSB is higher for more compressed audio. Why I say well worth noting is that I think a lot of people miss this when considering the benefits of CESSB. A more compressed audio benefits EVEN more from CESSB. The advantage of CESSB increases. 73 Hans G0UPL http://qrp-labs.com https://buymeacoffee.com/g0upl ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [email protected]
