Hi Mike, Thanks for the gain information. I am going to look at the the gain numbers and see if there is any correlation with the wildly different input impedances to the output lowpass filters.
For reference, I found the input Z to the filters to be as follows: 160: 63.8 +J1.6 80: 35.7 +J5.1 40: 42.0 +J5.8 20: 32.0 -J2.1 17: 51.0 +J3.1 15: 49.6 -J0.3 10: 60.4 -J2.9 6: 51.0 +J0.14 Looking at the component values of the output filters, it appears that the above impedances were by design. Which makes me wonder if it was an attempt to compensate for the poor saturation characteristics of the MOSFETs and leakage inductance of the output transformer of the MOSFET amplifier (KPA3A)? I am also finding in some cases that the K3s LPA (KLPA3A) has some problems of its own and does not like to play nicely with the input to the LDMOS K3s Retrofit Amplifier on 160 meters. I would however like to avoid redesigning LPA by compensating for its shortcomings in the LDMOS amplifier. Thanks again for your feedback. 73, Hal W7YNC > On 03/06/2024 3:07 PM PST Michael Carter via Elecraft > <elecraft@mailman.qth.net> wrote: > > > Hi Paul, > > For comparison, here are the 50 watt TX gain values from the > calibration I did last November when I installed > the KPA3A 100 watt PA in my K3 (s/n 67xx): > > 1900 kHz TXGain HP 10 > 3750 kHz TXGain HP 06 > 5336 kHz TXGain HP 08 > 7150 kHz TXGain HP 08 > 10125 kHz TXGain HP 08 > 14200 kHz TXGain HP 05 > 18110 kHz TXGain HP 05 > 21200 kHz TXGain HP 03 > 24930 kHz TXGain HP 03 > 29000 kHz TXGain HP 05 > 52000 kHz TXGain HP 04 > > Do you know if your 100 watt PA module > uses RF bipolar transistors or MOSFETs > (the KPA3A uses MOSFETs; the original KPA3 > uses bipolars)? > I don't know if the MOSFET version has higher gain > than the bipolars, but I suspect not. > > I've been in a separate conversation > with Hal, W7YNC, who is an LDMOS RF amplifier > designer professionally. There is some > uncertainty about whether the higher TX gain > parameters mean higher TX drive signal > amplitude or the converse. > > In any event, your TX gain values don't > have wild swings from band to band, > although the difference between 20 > meter and 30 meter gains is substantial. > > Perhaps some others who have done > TX gain calibrations recently (or could > repeat them) on K3 units with the > bipolar PA transistors could post > their results? > > 73, > Mike, K8CN > > ______________________________________________________________ > 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 dyno...@comcast.net ______________________________________________________________ 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
