One big issue with switching power supplies is their dynamic performance. An SSB transmission requires the power supply to be happy with a load that randomly varies between maximum current and the resting current of the PA. If the power supply does not have good dynamic regulation, that can cause distortion.
With a linear supply, the output filter capacitors have to be big enough to filter the 100 Hz or 120-Hz ripple anyway, so they automatically do a good job of smoothing out the variations due to the 300-3000Hz audio of the SSB signal. However, the filter capacitors in a switching supply can be much smaller since they only have to filter out the high-frequency ripple from the switcher. So the dynamic regulation depends on the feedback circuitry in the switching regulator. If it isn't designed in such a way as to provide low output impedance in the audio range, considerable distortion can result. Al N1AL On Thu, 2011-05-12 at 19:06 +1000, Gary Gregory wrote: > I would not be surprised to hear Eric and Wayne state that price was not > that big a consideration with regard to the power supply even though it > would have been one of the considerations. My bet is that IMD performance, > reliability, durability and maybe stable performance played a significant > role in their final decision. > > I have to say that given the testing I have done here the amplifier works > better than I expected. The quality I expected, but I still got a surprise > with the performance. > > I don't find the amplifier heavy but of course a switcher would have reduced > some weight but I doubt it would have provided any further benefit...ymmv > > 73's > Gary > > > > > > On 12 May 2011 18:45, David Cutter <d.cut...@ntlworld.com> wrote: > > > That's not to say that they didn't try. Unlike manufacturers who only make > > linears, Elecraft has a vested interest in making their product line > > friendly to all their products and a switcher would have to pass muster > > against their own sensitive receiver. So, Elecraft internal standard for > > noise is probably much higher than in the general market place. > > > > David > > G3UNA > > > > > > > Hello George, > > > > > > From my reading of all the replies both on and off-the-list, the main > > > reasons are: > > > > > > 1. it is cheaper to use linear PSU so that the price of KPA500 should be > > > competitive; > > > 2. maintenance and repair will be easier for a linear PSU; > > > 3. RFI is so often found in the switching PSU > > > > > > I put this question up in the reflector because I find ICPW-1, VL1000 and > > > TL933 are all using switching PSU. I think items 1 & 2 above have > > > explained the reason of using linear PSU in KPA500. > > > > > > Voltage fluctuation in the AC mains will affect the linearity of the PSU > > > in KPA500. However, this will not border me because the reliability of AC > > > power supply in Hong Kong is over 99.9%. We have never suffered from any > > > power interruption in the past years. > > > > > > See you all next week in Dayton. > > > > > > TNX & 73, > > > > > > > > > Johnny VR2XMC > > > > > > > I can not believe hams who do not want switching mode supplies in their > > > shack. This precludes the use of a computer in the shack. It also means > > no > > > TVs, printers, and a host of other products. There is also a false notion > > > that so called linear supplies do not cause RFI. Study Dirac's delta > > > function and you will understand why they can. > > > Love my two K3s > > > George, W6GF > > > > > > > > > > > > > One of the inviolable rules in the W6LX shack is: NO SWITCHING POWER > > > SUPPLIES. > > > > > > Not to make an incendiary statement, but *all* of them generate RFI. Many > > > people > > > will tell you that they've never heard RFI from their switching power > > > supplies, > > > but often it's just because they don't know what it sounds like or they > > > haven't > > > tuned across the right frequency. > > > > > > > > > Why raise the noise floor by even half a dB if you can help it? > > > > > > Nothing beats a old-fashioned, big, beefy, and quiet linear power supply. > > > > > > Al W6LX > > > > > ______________________________________________________________ > > 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 > > > > > ______________________________________________________________ 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
