Hmmm. Your advice to: "...*please* set it to 4 bars in soundcard "digital" modes..."
contradicts the direction given here (in step 7): http://www.elecraft.com/K3/k3_operating_tips.htm#psk%20audio viz. "You should not see any ALC bars on the K3 display (when set to CMP/ALC)" This always confused me since it didn't agree with the manual, but your explanation helps a lot, and I'll do it that way now. Bob NW8L On Sun, Apr 6, 2008 at 1:06 PM, Lyle Johnson <[EMAIL PROTECTED]> wrote: > There is apparently some confusion about how the K3 ALC works. Just to help > muddy the waters a bit, I'll toss in what little I know about it. > > We recommend setting the Mic (or LINE IN) Gain so you get 5 bars of ALC, > with possibly the 6th bar occasionally flickering, with CMP set to 0. > > No, this is not to ensure you have Tx distortion! Just the opposite, in > fact. > > In this case, the ALC meter display is acting as a "VU Meter" and is being > used to help you set the Tx audio path gain correctly. It is not showing > you how much you are over-driving the PA. This is why you can set it up in > Tx test mode, when you are not transmitting any RF at all. > > If you have a little too much drive, the DSP will scale things back at the > output of the mic amp. Thus at the 5th ALC bar, the DSP is at the threshold > of gain compression. At the 6th bar, it is cutting back gain by 6 dB or so. > > Assuming SSB, after the Tx signal is created from the audio, it optionally > goes through an IF clipper. This is engaged by setting CMP to a value other > than 0. > > After the optional clipper, the signal goes through a 15 kHz IF filter > followed by a gain section in the DSP, and is then output as a 15 kHz signal > to the rest of the Tx strip. > > From this point, the MCU watches things and if it sees power levels going > awry, severe mismatch, etc., it cuts back the drive to the Tx strip in the > DSP. Thus, the Tx strip is running at nominal gain regardless of the power > level. OK, if you go below 12 watts you are using the LPA and not the HPA, > so the Tx strip gain is less, but you get the idea. What we are *not* doing > is varying the bias on an IF amplifier somewhere that might change its > operating point and possibly introduce additional distortion. The point in > the DSP path where the change in drive is commanded is linear to the limits > of 32-bit floating point math and the resolution of the Digital to Analog > converter. > > Enjoy! > > 73, > > Lyle KK7P > > [ Note: For PSK and other operation, you want to set things to the level > where the 5th bar just comes on -- or just doesn't. If you have only 4 bars > in digital modes, that's OK. With less than 4, you are under- driving things > and the ALC will kick in to bring up the power level to the amount you > requested. If you try and trick the system and run with *zero* ALC bars in > PSK31, the ALC has to work hard to give you your requested power - or maybe > it will think there is insufficient signal to work with - and your Tx S/N > may suffer. So, *please* set it to 4 bars in soundcard "digital" modes. ] > > _______________________________________________ > 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
