Roger, You should see the crummy "DC" waveforms put out by typical laptop switching supplies. I bought a bunch at a recent hamfest. Put each one on a 'scope to observe the output. One had a 0.5 volt sawtooth superimposed over the DC value. Another have ringing with introducing a swing of over a volt in magnitude around the DC value. I tested at zero and full load. None of these problems went away. The rest were far from clean. Some were IBM branded.
No way would I put my rig on one of these beasties. I don't know how laptops manage to tolerate them. The only other thing is yes were hamfest items and could have all been rejects or something. For what it is worth, I did find one good supply but it was for a Kodak printer. However, it put out 25 volts. The output was very clean at all levels of load. 73 de Brian/K3KO On 5/10/2011 19:35, Ross Primrose N4RP wrote: > On 5/10/2011 3:13 PM, Jim Brown wrote: >> If it were my radio, I would add one or two silicon diodes in series >> with the positive lead to reduce the voltage to about 14 volts. For a >> 10W K3, I'd guess that 5A diodes would be just fine. > > I'd thought about that as a possibility. Heat could be an issue, > especially if I want it to be easily portable, at 5A, that's about > 3.5W/diode assuming a 0.7V drop. > >> If it's a laptop supply, I would also be concerned about RF noise that >> it might produce. > > I'm concerned about it too, but the laptop supply is already in hand, > and without a laptop, so it's worth a try. I know the old desktop PC > supply I'm using now has broadband noise at 7.070-7.080, so maybe this > one will be better (and definitely a lot smaller!). > > 73, Ross N4RP > ----- No virus found in this message. Checked by AVG - www.avg.com Version: 10.0.1325 / Virus Database: 1500/3628 - Release Date: 05/10/11 ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
