My internal K3 readings of 14.3V idle and 14.0V at the 35w PEP out needed to drive my Alpha 8410 to 1200 or 1300 watts out, probably is pretty good IMD. The idle current is ~1.3 amps. Tune at 35 watts into 1:1 SWR is 8.7 amps. That's .04 ohms in the cabling. I don't have anything to directly measure that.
At that point, the tuning of the Alpha would has more to do with the over-the-air IMD than the K3. Wouldn't predistortion need to be external to the K3, dynamic based on sampling the output of the amp, and converted into some DSP friendly format fed to the K3 CPU? 73, Guy K2AV On Thu, Oct 29, 2015 at 3:52 PM, Joe Subich, W4TV <li...@subich.com> wrote: > > CW is just one mode and is the easiest to "get right" as far as the PA > is concerned. CW bandwidth is determined primarily by keying shape and > phase noise in the synthesizer (or D to A clock jitter). > > The K3/K3S is far from the cleanest rig when it comes to SSB on any of > the audio based digital modes. All of the rigs using 48V finals have > IMD products many dB less than the K3/K3S - particularly when the > K3/K3S is being run from a partially discharged battery. > > However, even rigs with 48V finals are notably more dirty than many of > the rigs that used tube type finals (particularly the 6146) of 40 years > ago. > > Amateur rigs need predistortion - particularly those with "12V" finals - > to get SSB (and data mode) IMD below -50 dBc (-44 dB PEP) as a starting > point or "12V" radios should be limited by their makers to 60-80W where > the IMD is much lower than at 100-120W levels. > > For ARRL to have silently watched transmit IMD degrade by nearly 20 dB > in the last 40 years and not raised the issue is unconscionable. > > Lest anyone think I'm picking on Elecraft ... the IMD issues are the > same in many solid state amplifiers, they are rated for saturated > conditions which drive up IMD. Most are significantly less dirty when > operated at 60-75% of rated PEP output unless the designer has built in > a significant amount of negative feedback. When a 1200W PEP amplifier > has only 8 150W transistors or or a 600 W amplifier has only two 300 W > transistors that's a good sign the amplifier can not possibly be clean > at its rated output. > > 73, > > ... Joe, W4TV > > On Thu, Oct 29, 2015 at 2:58 PM, Jim Brown <j...@audiosystemsgroup.com> >> wrote: >> >> According to ARRL measurements, the K3 produces the cleanest CW signal of >>> any current rig. See my summary of their published data in the following >>> link >>> >>> k9yc.com/TXNoise.pdf >>> >>> See my measurements of my K3 and several other rigs in this link >>> >>> http://k9yc.com/P3_Spectrum_Measurements.pdf >>> >>> 73, Jim K9YC >>> >>> ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:Elecraft@mailman.qth.net > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > Message delivered to k2av....@gmail.com > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
