> set the power control to the proper drive, and forget the ALC? ALC > doesn't fix leading spikes anyway, so what's it good for?
Arguably, ALC helps to function as a time-averaging RF level control that can protect against ongoing over-drive but not necessarily peak power busts. What I don't like about traditional ALC are the unknown side-effects (e.g., non-linearity) that can occur as a result of level-setting and timing differences between the transmitter and amp. Dynamic monitoring for amp SSB non-linearity can be accomplished with reasonably good accuracy using a scope in trapezoid mode. However, once transceivers began introducing delay as result of DSP, it's become nearly impossible to use the trapezoid method to look at system linearity of both the transceiver and amp, and the corresponding ALC effect. Other methods for measurement are probably beyond the cost and effort at most stations. Since the input Z of most solid-state amps is well-controlled at 50-ohms, that the input Z should not appreciably change as output Z changes, then can't we simply use a feed-forward ALC system instead of feedback ALC? A fast RF voltage peak detector can be bridged across the amp's input Z. When the RF voltage exceeds ~ 70.7Vpk, correction bias is applied to the solid-state PA. Simultaneously, a 3dB pad could then be inserted at the amp input until average input power drops below 50W. With the exception of the pad, the SPE amp works like this -- only it has a fault summing network that looks at half a dozen other parameters, all of which instantly apply MOSFET bias through the summing network to cut-off RF, and place the amp in bypass when any one of the non-ALC faults occur. Paul, W9AC ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
