Hi Jerry, The setup for the K3 in PSK31 is quite different from the way you set up most other radios. See <http://n2.nabble.com/K3-Transmit-IMD-td466326.html#a466329> for an explanation. There was a discussion about this just over a month ago on this reflector, as a result of which I personally changed my practices considerably from what I had been doing before with another radio.
As I understand it, the first 5 bars on the K3's ALC meter are not really ALC readings, at least not in the same sense they are on other radios. Provided your power control is set properly, you can have 5 bars reading on the ALC meter without any significant increase in IMD (as measured at my station with a PSKmeter in passive measurement mode). It appears as if the first 5 bars on the ALC meter are really just audio level readings (like a VU meter), and it's only after that point that the ALC actually kicks in. Even after the K3's ALC kicks in at 5 bars, it does not seem to introduce non-linearity, which is a drastic change from how many other radios behave. The appropriate way to set up for PSK31 appears to be the following: First, set the power control to the desired power setting. For PSK modes, I'd suggest making sure it is no higher than 50 watts. I believe this may actually be the most critical setting. If your power is set higher than 50 watts average, then if your Line In level is high enough so that your average power can exceed 50 watts, you could have instantaneous peaks that exceed 100 watts. If these instantaneous peaks go into clipping, you will have IMD regardless of the ALC meter reading. By setting the requested power to 50 watts or less (5 watts if you don't have a KPA3), you prevent the signal from going into clipping on instantaneous peaks. Next, adjust the Line In level with the Mic gain control until you get four to five solid bars on the ALC meter. This should allow you to get your average power on PSK31 up close to the desired power setting without IMD. Actually, in my experiments I could push the Line In setting higher without any apparent ill effects, but without increasing power either. There doesn't seem to be any point to doing this, though. As for AFSK RTTY, that is not sensitive to non-linearity - it's like CW. You can quite happily run AFSK RTTY at 100 watts power with 5 bars showing on the ALC meter and still have a clean RTTY signal. I have my digital mode software set up to switch the K3 automatically into DATA A mode with a power setting of 50 watts for PSK31, and to AFSK A mode with a power setting of 100 watts for RTTY. My sound card volume control is set low enough to avoid non-linearity in the sound card, and the Line In setting is set just high enough to reach 5 bars on the K3's ALC meter (LINE 8 in my case). So far that seems to be working just fine. The biggest limitation may well be heat dissipation. I often operate with the PA temperature display showing in the VFO B readout. For short contest-style overs in RTTY, the finals hardly even get warm, but for longer overs such as ragchews in PSK31, they heat up quite a bit even at 50 watts, and the fans seem to work a lot harder than they do in CW. One peculiarity I notice is that while I am transmitting, the temperature reading seems to be lower than during receive. I suspect that this may be due to the drop in supply voltage at higher current draws (even with a stiffly regulated power supply, resistance in the supply cable will result in a drop in voltage at the radio). Anyway, the net result is that in RTTY the fans may be on while the radio is receiving, then turn off when the radio goes into transmit, only to come back on again as soon as the transmission ends(!) My 2c worth. 73, Rich VE3KI K3 #1595 _______________________________________________ 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
