David, Bandwidth might not be a good argument. I'm not convinced ALC transients are a major universal problem with SSB signals when they are compared to other reasons for bandwidth problems. This isn't the appropriate forum for that discussion.
I have looked at ALC overshoot because of my connection with amplifier designs and failures in semiconductors and other sensitive components caused by ALC problems, and the pulse duration is very short. That short pulse repeats only after the ALC has discharged significantly, so the transmitter's gain is high. The problem is a great deal like automatic bias, where the leading edge always causes some distortion as the circuitry changes states. The deeper the bias, the more time it takes to remove it and the stronger the unwanted off-channel energy. ALC is a little worse because the control signal is sampled after some delay and has to wrap back around to the start. This means no matter what they do in the amplifier the cannot cure the leading edge problem. The one exception would be if they held the ALC voltage high and then pulled it down to a level that allowed proper drive. They may be doing that, but an indicator would be a slow power rise on the leading edges. It is a mirror of normal ALC. As for bandwidth measurements, I'm not convinced the WaveNode is good at transient analysis. With FFT analysis, the window where waveform is sampled has to be present at the same time as the transient, and the processing cannot average the power. It has to calculate to provide bandwidth information of the very short duration peaks. The problem is much like the reason a conventional spectrum analyzer will miss ALC problems in all but a few really severe cases. If it isn't sampling the transient frequency when it is there, the extra bandwidth doesn't show. I'm not convinced at all, because the overshoot is so short, it is the major problem we hear on the air....or even a significant one. I'm not convinced, and actually think it unlikely, the WaveNode could measure such a short burst. All that aside, because it is a big discussion, we are left with the fact Elecraft has clearly warned to NOT do 100% power control with an external ALC source. That warning is 100% understandable based on the unique way the K3 ALC works. It is absolute common sense the K3 ALC should not be replaced with a traditional external ALC for primary power level control. Even without Wayne's warning, I would not do it now that I understand how the K3 ALC works. To prevent splatter, the K3's internal pre-filter ALC must have primary control of power limits. The amplifier should only provide a fail-safe control that pulls back or kills the exciter drive if limits are reached. By the way, I'm testing new PA module designs with an IC706. It has terrible ALC overshoot. It has "100-watt plus" transients when I have it set at 20 watts to drive the PA modules. The K3 does not. Fortunately the MRF-150's are able to handle the 600% overdrive bursts from the IC706 without failure. I keep a couple ICOM's around just for that reason. I cannot test for PA module survival with a bad ALC system in the exciter using the K3, unless I ran the K3 power on full and used an external ALC detector system. Then I could make the K3 emulate the IC-706. Why would people not testing things want to do that???? 73 Tom ______________________________________________________________ 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
