> I predict that the power supply claim will turn out to be > bogus. The K2 has voltage regulators all through it, and > runs well down to -- is it 10 volts?
Before making statements like that please look at the K3 schematics. Power for the KPA3 is taken from the power supply input immediately after the RF choke, to J67B/P67B, through R3 (the current sense resistor for the metering), to J78B/P68B and to the final amplifier transistors via an RF filter. There is absolutely no regulation of the Vcc applied to the push-pull 2SC2782 pair used in the KPA3. I can guarantee that running the KPA3 will result in low power output (80 watts?) with significant IMD at that level. 73, ... Joe, W4TV > -----Original Message----- > From: [email protected] > [mailto:[email protected]] On Behalf Of Peter Wollan > Sent: Tuesday, January 27, 2009 1:48 PM > To: [email protected] > Subject: Re: [Elecraft] SSB IMD > > > This is possible, but, as far as I know, it is untested. > I've read several anecdotes claiming poor SSB performance, > and several others claiming excellent SSB performance. > What's needed is for someone to take one of the "poor" K3's, > and change some factor that turns it into an "excellent" K3. > Such as, plug it into a better power supply, and show that > one power supply consistently produces good results and > another consistently produces bad results. > > I predict that the power supply claim will turn out to be > bogus. The K2 has voltage regulators all through it, and > runs well down to -- is it 10 volts? The K3 needs a bit more > oomph, but I'll bet Wayne designed it to be robust, too. I > further predict that the bad SSB performance will turn out to > be either an adjustment issue, or an external amplifier > issue. I'd love to see some experiments. > > Peter N8MHD > > On 1/27/09, Joe Subich, W4TV <[email protected]> wrote: > > > > > > > Is there something critical in the radio that > > > gives this outcome? Critical adjustment perhaps? > > > Is it very sensitive what PS we use (ala W4ZV)? > > > > Yes, it is very sensitive to power supply voltage. > > Look at any of the application notes - the one > > Craig mentions for the P-P RD100HHF FETs is a > > good example. Decreasing Vcc (or Vdd) by just > > one Volt will increase the IMD at 100 Watts by > > 10 dB and decrease the maximum output power by > > almost 20 Watts. > > > > Running the power supply at 14.0 - 14.5 Volts and > > using a power supply with good dynamic regulation > > will go a long way to keeping the K3 "clean." > > > > 73, > > > > ... Joe, W4TV > > > > > > > -----Original Message----- > > > From: [email protected] > > > [mailto:[email protected]] On Behalf Of > Jan Erik Holm > > > Sent: Tuesday, January 27, 2009 1:54 AM > > > Cc: [email protected] > > > Subject: Re: [Elecraft] SSB IMD > > > > > > > > > Yes I´ve seen those figures, there are are lot of > > > data from component manufactures however by the > > > time we see the finished product data doesn´t > > > even come close. > > > > > > I tried to look for the data on the FT-990 that > > > K6LL informed about but couldn´t find it. I was > > > thinking what reference level they used, I think > > > I remember ARRL changed their procedure, the -38 > > > prity well could be -32 in real life. > > > > > > However, something struck me, why is it we see > > > this big variation in data on the IMD3? We have > > > a spread between -38 to -24 dB. A number of > > > people has measured below -30 dB and as far as > > > I know "only" one around -38 dB. Who is right > > > and who is wrong? > > > Is there something critical in the radio that > > > gives this outcome? Critical adjustment perhaps? > > > Is it very sensitive what PS we use (ala W4ZV)? > > > > > > As I said before, here I am first time on 20m > > > SSB and people report trash around my signal, > > > i e bad IMD. However at that time I had K3 at > > > 120W, aftter I´ve made measurements and it > > > looks like something slowly starts to happen > > > at 80W. > > > Also I have myself heard K3´s on SSB with "trash" > > > around the signal "however" I have also heard > > > K3´s that did NOT have that. > > > So what´s going on here, I´m getting reel puzzled > > > and frankly quite tired of this. > > > > > > I wish there would be a "service manual" available, > > > like there is for any Japanese rice box. I mean > > > a manual that contains all data for all adjustments. > > > Why not?? > > > > > > / Jim SM2EKM > > > --------------------------- > > > Joe Subich, W4TV wrote: > > > > > > > >> Jan Erik Holm wrote: > > > >>> Bill and others, hold on and think about these > > > >>> figures. -35 to -38 dB IM3 !! We are dealing > > > >>> with 2SC2782 transistors operating at around > > > >>> 12V DC. I say no more, the knowledge and intelligent > individual > > > >>> will understand. > > > > > > > > I would be careful here ... the Toshiba 2SC2879 data > sheet clearly > > > > does -38dB IMD at 60 watts with VCC=12.5V. There are certainly > > > > devices capable of that level of performance means that > there are > > > > devices capable of that level just as there are devices > capable of > > > > similar levels of performance at 120-140 watts per device with > > > > Vcc=28V. > > > > > > > > I would expect the 2SC2879 to also be capable of this level of > > > > performance ... if not, I would have expected the design of the > > > > KPA3 to have been based on another device. > > > > > > > > 73, > > > > > > > > ... Joe, W4TV > > > > > > > > > > > > _______________________________________________ > > 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 > > > _______________________________________________ > 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 _______________________________________________ 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
