wayne, After you have the K4 fully put to bed, for your next project you might want to consider an amp that is directly driven by an I/Q stream. The amplifier will be much more efficient (less power consumption) and you start out with less IMD before any pre-distortion.
Sent from my iPad > On Sep 13, 2020, at 6:05 PM, Wayne Burdick <[email protected]> wrote: > > Hi JR, > > Virtually all class-AB-biased amplifier stages have worst-case 3rd-order IMD > in the range of -30 dBc (ARRL method) on some HF bands. This reflects a > limitation in the state of the art. Even with adequate feedback and bias, an > amplifier operated in the vicinity of its 1 dB compression point (where it is > most efficient) will exhibit such characteristics. > > To improve on this you either need to operate class A, which is highly > inefficient, or use predistortion. > > A small number of commercial transceivers are now providing predistortion, in > some cases as an optional/experimental setting (that not everyone uses, or at > least not all the time). There are constraints on predistortion power range > imposed by the headroom limit of the amplifier stage itself. Go over that > point and distortion will be worse than without predistortion. > > Predistortion, correctly applied, can reduce interference between adjacent > stations on a crowded band. This is a factor at least some fraction of the > time during typical amateur radio use. Beyond that, the motivation for a > “pure“ signal exemplifies the amateur spirit of cooperation, and is an > example of keeping the hobby on the forefront of electrical design. > > Wayne, > N6KR > > ---- > elecraft.com > >> On Sep 13, 2020, at 2:34 PM, JR <[email protected]> wrote: >> >> Why are so many ops obsessed with predistortion? >> >> The Elecraft K-Line already produces some of the cleanest, purest transmit >> signals around. Do we need predistortion ? If so, why, and how much >> better is it than what we already have? Should I wait to buy a new rig >> until that is available? >> >> Thanks and Happy Trails to all. K8JHR >> _________________________________ >> ______________________________________________________________ >> Elecraft mailing list >> Home: http://mailman.qth.net/mailman/listinfo/elecraft >> Help: http://mailman.qth.net/mmfaq.htm >> Post: mailto:[email protected] >> >> This list hosted by: http://www.qsl.net >> Please help support this email list: http://www.qsl.net/donate.html >> Message delivered to [email protected] > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[email protected] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > Message delivered to [email protected] ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [email protected]
