++++++++++++++++++++++++++++++++++++++ Date: Sun, 22 Oct 2000 08:05:10 -0400 From: "Bob Lewis" Subject: Re: [Elecraft] PSK-31 Mod > Keep in mind that the ALC is no more than a gain control. It is not a > clipper or compressor. I disagree. The ALC decay time on the K2 is fast enough that it does provide some "compression" of the audio signal and it does (or at least mine does) flatten the peaks of the PSK waveform and introduce IMD. How much flattening and how much IMD depends on how much ALC reading you have. For PSK there should be *no* ALC reading on the K2. Turn down the audio drive from the sound card (or insert additional attenuation in the mike line) until there is no ALC action. Yes, the ALC provides automatic control of the gains on SSB but you must not let it do so on PSK if you want a clean signal. The total gain of the K2 transmitter changes from band to band so if you want to operate with maximum clean power output (just before any ALC action) you will need to readjust the sound card output for each band. If you set the level correctly on 10 meters, you'll be overdriving on 80 meters. The better solution is probably to set the levels on 80 meters and accept less power output on 10 meters. The difference between 5 watts peak output and 3 watts peak output doesn't matter much on PSK anyway and you don't have to remember to readjust things when changing bands From: "Bob Lewis" Subject: Re: [Elecraft] PSK-31 Mod Just for info on how I came to the conclusion that K2 ALC does indeed impact the IMD here are the tests I ran: 1) The K2 is connected to a sound card via a pot so I can adjust the audio drive level without changing any sound card or computer settings. The K2 is transmitting into a dummy load. Across the room is an IC761 with a second computer and sound card. The S-meter reading on the IC761 is an S2 - S3 so I'm sure that I'm not overdriving the IC761. With the audio drive set below any ALC reading on the K2 it read the IMD on the receiving station (using digipan). As I increase the audio drive and begin to see an ALC reading on the K2, the IMD reading gets worse. 2) I put a scope across the dummy load on the K2 setup. As I increase the drive and begin to see an ALC reading I can see the PSK waveform peaks flattening on the scope. 3) I put the scope on the K2's ALC line and can see a small PSK-like waveform, proving that the ALC voltage is changing in response to the waveform. +++++++++++++++++++++++++++++++++++++ Date: Sat, 21 Oct 2000 15:04:50 -0700 From: "Ron D'Eau Claire" Subject: RE: [Elecraft] PSK-31 Mod J. Ellis asked: "When you run the radio on PSK, do you turn the power all the way up and only drive it to 5 watts or so? That is the way I have been doing it and it seems happy. I guess I am concerned that if I set the power level to 5 watts or so, that when driving it to 5 watts, I'm going to start clipping. Is that correct or not?" No. The K2 will not clip or compress the audio unless you massively overdrive the microphone input, or you turn the audio compressor on. The audio compressor is controlled by the SSBC menu selection. 1-1 is no compression and that's what you should use for PSK. It's easy to forget and leave it on if you work SSB, since normal SSB operation seems best at 1-2 or above, where the compressor is active. I set the audio input from my PC so the K2 puts out the same RF power in PSK idle that I see in TUNE. The K2's internal power meter displays the 'peak' RF output power in SSB mode, so it will read much higher than an 'averaging' meter. Checking the ALC display, the first bar is just barely flickering. That doesn't mean that it is clipping, but just that there is enough audio coming in to let the automatic level control start adjusting the audio gain. Elecraft says that normal ALC control is indicated by 1 to 3 bars flickering with the bargraph display in ALC mode. Keep in mind that the ALC is no more than a gain control. It is not a clipper or compressor. There is no manual 'mic' gain adjustment in the K2, the ALC circuit takes care of that for you. One to three bars flickering means that there is enough audio at the mic connector for the ALC to be monitoring and controlling the audio gain for normal, undistorted modulation. I do limit the output power to 10 watts. According to the Elecraft folks, the K2's IMD deteriorates above 10 watts. Be listening (watching?) for your sig! Ron AC7AC K2 # 1289 +++++++++++++++++++ RE: Adjusting K2's Signal Power for PSK31 when changing frequencies........ --------- Date: Tue, 20 Nov 2001 09:33:55 +0000 From: "Julian, G4ILO" Subject: Re: [Elecraft] K2 as main station? I use a software approach for this, not hardware. I leave the Windows mixer output panel on the desktop so I can adjust the audio level with the mouse. To make it easily accessable, create a shortcut on the desktop containing the command "C:\WINDOWS\SNDVOL32.EXE /p" . - -- Julian, G4ILO. (RSGB, ARRL, K2 #392) Homepage: http://www.qsl.net/g4ilo "bob baxter" wrote: I haven't found that they change considerably from band to band -- maybe from 80m to 10m. However, I replaced the fixed resistor in my transmit interface with a pot and, when I change bands, it just takes a couple seconds to re-adjust the output to just extinguish the first ALC bar. Bob Baxter AA7EQ Bisbee, Az. +++++++++++++++++