> Perhaps I'm just being dim, but why is TXG necessary at all? > Why can't you just turn the mic gain up until you have plenty > of drive, and then use the power control to set the output > power using the ALC?
Traditional ALC operates by overdriving the final amplifier. It senses grid current Which is an indication of overdrive and uses that to turn down the drive. Previous generations of solid state radios turned to sensing output power for the level reference. However, those "after the fact" ALC circuits have two serious issues ... first overdrive must have already occurred to generate an ALC signal and overshoot is certain but there is also no protection against overdrive and distortion in the low level intermediate stages. The K3 generates its ALC in the early stages (the DSP) using a feed forward technique that delays the RF to allow the control signal proper effect. By controlling the level early in the transmission chain, the K3 ALC prevents overshoot, protects against distortion due to RF compression or clipping after the "masking filter" or "channel filter" and eliminates distortion due to ALC "hunting" (the effects of ALC constantly overcorrecting then under correcting). Instead of using a short ALC time-constant (which causes the "hunting" distortion in conventional designs), the K3's power level control can almost have a fixed gain with only a slow time constant for fine adjustment. However, since the power control really sets the average power (e.g. CW), there must be some compensation for differences in the peak to average power ratios of various voices, the level of compression/clipping in use and different modulation types (particularly some data modes with very high peak to average ratios) so that operations with minimal clipping or modes with high peak to average power ratios do not overdrive the driver and PA on peaks even though the "average" power is well below the level that has been set. > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of Julian, G4ILO > Sent: Saturday, October 25, 2008 6:17 PM > To: [email protected] > Subject: RE: Re: [Elecraft] K3 Beta firmware rev. 2.57 > > > > > > Joe Subich, W4TV-3 wrote: > > > > > > I don't know ... it seems to work properly here. If you elect > > to not make it global, it may be necessary to provide separate > > TXG settings for voice (SSB), AM and AFSK A/DATA A (DTA) ... or > > at least SSB/Data and AM. > > > > > Perhaps I'm just being dim, but why is TXG necessary at all? > Why can't you just turn the mic gain up until you have plenty > of drive, and then use the power control to set the output > power using the ALC? That's all I recall having to do on other radios. > > ----- > Julian, G4ILO. K2 #392 K3 #222. > http://www.g4ilo.com/ G4ILO's Shack > http://www.ham-directory.com/ Ham > Directory http://www.g4ilo.com/kcomm.html KComm for > Elecraft K2 and K3 > -- > View this message in context: > http://n2.nabble.com/Re%3A-K3-Beta-firmware-rev.-2.57-tp137495 4p1377026.html Sent from the Elecraft mailing list archive at Nabble.com. _______________________________________________ Elecraft mailing list Post to: [email protected] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com _______________________________________________ Elecraft mailing list Post to: [email protected] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
