Not doubting your TX IMD report in PSK. But I typically see ~-32dB IMD when checking PSK at 50W.
------------------------- 73, Greg - AB7R Whidbey Island WA NA-065 On Mon Jan 26 7:58 , "Julian, G4ILO" sent: > > > >David Cutter wrote: >> >> Is there a "sweet spot" to which one can adjust the power output for >> minimum IMD, if so, how would you do it easily? I presume you would need >> another rx or spectrum analyser. And I bet it changes with antenna >> reflections, ie from one end of the band to the other. >> >> I dare say a lot of K3s are followed by linears which add even more IMD, >> so, it might be tricky to optimise for the station as a whole and not just >> at minimum drive from the K3; perhaps a power pad is needed, but who would >> bother ? >> >> It is hoped that the Elecraft linear might take this into account. >> >> > > >TX IMD just goes on getting worse as you increase the power. It starts >getting worse much more quickly as you approach and then exceed the maximum >rated power. So your "sweet spot" would be "as little power as possible." :) > >The issue with the K3 is that the transmitter does not seem to be as clean >as is possible with the "state of the sart", even given the restrictions >imposed by having a 13.8VDC supply. I am only able to make PSK31 IMD >measurements which are not directly comparable with two tone measurements >usually used for SSB transmitters, but I assume that they both reflect upon >the TX amplifier linearity, or lack of it. > >My K3 goes from -30dB at 2W to -22dB at 12W. > >My K2 goes from -29dB at 2W to -27dB at 14W (both measured on 30m). > >Therefore it seems to me that my K2 has a cleaner transmitter (at least as >far as IMD goes) than my K3, which I find surprising since the K2 was built >my me nearly 10 years ago using only the barest minimum of test equipment, >whereas the K3 low power PA module was aligned and tested by Elecraft with a >lab full of equipment. > >It seems to be the way on this reflector that anyone who makes any criticism >of anything Elecraft makes comes in for a lot of abuse and ridicule. But I >wonder whether those who claim the TX IMD of the K3 is poor actually have a >valid point, but their K3s are just not as well set up as those belonging to >people who don't see anything wrong with them? > >It seems unlikely to me that Elecraft would deliberately choose a worse >design of PA for the K3 than that used successfully for years in the K2. Yet >the figures I just gave seem to suggest that considerably better performance >is possible. Obviously, my test results are for the QRP version. But if the >signal going in to the 10W PA is not as good as it could be, the output is >certainly not going to be any better. > >----- >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/6-Meters-tp2213777p2218679.html >Sent from the Elecraft mailing list archive at Nabble.com. > >_______________________________________________ >Elecraft mailing list >Post to: Elecraft@mailman.qth.net >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: Elecraft@mailman.qth.net 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
