Unfortunately neither the Toshiba or ASI datasheets for the 2SC2782 used in the KPA3 provide any IMD specifications. Unlike the information available for the 2SC2879.
The 2SC2879 has a distinct "sweet spot" at 60 Watts output with 12.5V and 100 mA idle current. A push pull pair of 2SC2879 (e.g., FT-990) would be expected to produce -38dB IMD at 120 watts at the collector (100 W from the LPF) with 8 - 10 W of drive and Vcc 12.5V at 28 MHz. Note that the 2SC2879 is also rated for -24dB IMD at 100 Watts per device (or 200 W PEP from a pair) ... there is no such specification for the 2SC2782. I haven't been able to find IMD data on the low level devices for either the FT-990 (2SC2166 predriver, 2SC3133 drivers) or K3 (RD06HHF1 predriver, RD15HVF1 drivers). However, I am a bit concerned that the K3 predriver is only rated for 30 MHz operation! 73, ... Joe, W4TV > -----Original Message----- > From: [email protected] > [mailto:[email protected]] On Behalf Of Dave > Hachadorian > Sent: Monday, January 26, 2009 11:42 AM > To: Elecraft reflector > Subject: Re: [Elecraft] TX IMD > > > There is something that has been puzzling me for the last 17 years. > > In November of 1991, QST reviewed the Yaesu FT-990, which > used a 13.8 vdc PA. Worst case measured 3rd order IMD > was -38 dB, 5th order was -47 dB. This measurement was at > 100 watts output. The review is available on ARRL's > members-only web site. > > ARRL had this comment, "It's refreshing to see that it's > possible to make a 100-W MF/HF radio with low voltage finals > AND such low-distortion transmitter performance". > > As far as I know, no ham 13.8 volt radio has even come close > to this TX IMD performance ever since. Looking at the 990 > PA, there's a 2sc2166 predriver, a pair of 2sc3133 > drivers, and a pair of 2sc2879 finals, all npn transistors, > nothing exotic. > > So what was Yaesu's secret, and why hasn't anyone else even > come close? > > Dave Hachadorian, K6LL > Yuma, AZ > > > > > > > > > > > > > > > > > > > > > > > > > > . > > _______________________________________________ > 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
