The RD06HHF1 used in the Low Power Amplifier in the K3 is NOT rated to only 30 MHz. It does carry a specification for 6 watts power output and 16dB gain at 30 MHz, perhaps for services at 27 MHz, but further down the data sheet are S parameters all the way to 1000 MHz indicating a much wider range of useful operation. The RD06HHF1 as used in the K3 operates at an output power of only about 1 watt. Furthermore, when the K3 is equipped with the 100 watt KPA3, the low power amplifier operates at about 5 watts output. At this level the contribution to total IMD is negligible.
73, Bob, N6CM On Mon, Jan 26, 2009 at 1:14 PM, Joe Subich, W4TV <[email protected]> wrote: > > 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 > _______________________________________________ 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
