I get that in general given all the various TRX out there. But for the K3, the digital functions in firmware do a far better job of signal management before the signal is ever analog, much less RF, which can include pre-compensating for issues in the analog circuits. Much of the talk seems to assume that level control can only take place in analog circuits with their limited portfolio of tricks. The digital effects all of those, and others not possible in analog, accomplishing it all before DAC.
While over time some number of K3 TX level issues have been reported and fixed by Elecraft, none of those have been solved by analog circuit changes, all done in firmware. It seems that the STRATEGY of using a feedback voltage from the amplifier is obsolete. The Expert amp has a very quick protection circuit that kicks in before damage can occur. If the protection function of AGC feedback voltage is handled well by the amplifier using other means, there is nothing to be done by AGC using a TRX like a K3. 73, Guy On Wed, Apr 21, 2010 at 8:54 PM, Paul Christensen <w...@arrl.net> wrote: >> 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
