I have a Codan 6924 lunch box radio that does just this. ( http://www.hfradiosales.com.au/codan_%20barrett_hf_radio_information/RADIOS/files/6924%20MK2-2.jpg )
It takes in 10-15V and boosts it to 28V to feed a 25W PA, it does so only on TX. This radio was designed in 1969 and released to market in 1971, I got mine given to me in 1979. So this concept is not new. Way back when the 28V RF transistors of the day did not operate well with low collector voltages at 12V, IMD was way too high. For reference the 6924 IMD is better than -40dB PEP for a 38 yr old radio. I believe we will see a return of the 50V MOSFET PA's in commercial equipment again, especially with the explosion of LDMOS devices and the ever decreasing availability of 16-18V bi-polar RF transistors. 73 Matthew VK5ZM On 21 February 2017 at 09:10, Mel Farrer via Elecraft < elecraft@mailman.qth.net> wrote: > I have long wondered why some manufacture did not think of it. That is a > amp with built in 12 VDC boost PS. With all of the new switching tech, it > should be a KISS solution and make the amp SOUND GREAT all of the time.... > Just my opinion hi. > Mel, K6KBE > > From: Bill Frantz <fra...@pwpconsult.com> > To: elecraft@mailman.qth.net > Sent: Monday, February 20, 2017 2:08 PM > Subject: [Elecraft] Boost power supplies for RF amps > > The short answer is they can. It is only a matter of engineering > time, cost, resulting price, number of customers and competing > projects. In other words, the usual business considerations. > > Lets work the idea through for several of the Elecraft RF amplifiers: > > The 10-15W K3(s) amp: This amp can have significant IMD at low > voltages as we have discovered with our QRP, all Elecraft, field > day operation. The KX3 seems to do better, so reengineering the > amp may be a better solution. For field day, we try to have > fresh batteries available. > > The 100W K3(s) internal amp: This amp also has low voltage IMD > as we found during our 100W California QSO party expeditions. > But, consider the K3(s)'s construction. The front of the radio > is the digital portion, including the DSPs and the front panel > computer. All of this digital noise is isolated from the analog > circuits in the back of the radio. If Elecraft were to include a > boost power supply with the internal amp, that high-current > switcher would be in the analog section, and probably impossible > to quiet. Solution: Get an external boost power supply. > > The KXPA100 external amp: This form factor would be an ideal > place to include a boost power supply. The use profile includes > portable battery operation and designing isolation for the power > supply into the package seems straight forward. > > The KPA500 external amp: The amp setup procedure sets the > voltage to to 65v to 85v and the specifications call for about > 1000 VA of power or about 13A at 75v. That would be nearly 75A > at 13.5 volts assuming 100% efficiency, so it would be a good > idea to put the boost power supply next to the battery and run > 75v to the amp. It would make a nice high power mobil rig. > > 73 Bill AE6JV > > In thread "Re: [Elecraft] Chinese ebay amps for KX3", on 2/20/17 > at 5:47 AM, pin...@erols.com (Charlie T, K3ICH) wrote: > > >So now, tell me why a mid-sized radio can't have a built in 12 V to say, > 50 > >V converter to drive some HV FETs for cleaner output specs like the Yuge > >radios. > ----------------------------------------------------------------------- > Bill Frantz |The nice thing about standards| Periwinkle > (408)356-8506 |is there are so many to choose| 16345 > Englewood Ave > www.pwpconsult.com |from. - Andrew Tanenbaum | Los Gatos, > CA 95032 > > ______________________________________________________________ > 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 farrerfo...@yahoo.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 vk...@bistre.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
