On 12/21/2010 10:11 AM, George A. Thornton wrote: > Amplified computer speakers have been a problem for me. They are not > well screened for RF and on occasion I have had bad feedback problems.
Yes, amplified loudspeakers (that is, speakers with built-in amplifiers) are notorious for serious RFI problems, thanks to poor shielding, poor circuit board layout, poor input filtering, and Pin One Problems. I work in the world of pro audio, and take a VHF/UHF talkie with me to trade shows to test for RFI immunity in various products. Over a period of about ten years, I've seen only a couple of RFI-proof loudspeakers, and they were in the $3K range. And I've seen lots of loudspeakers in that range (or even higher) with nasty RFI problems. :) The loudspeaker output stages in the K3 are sufficient to drive an external passive (unamplified) loudspeaker of reasonable efficiency to a more than enough level for those who aren't seriously hearing impaired. A number to look for in loudspeaker specs is 85dBSPL or more for 1 watt at one meter into 8 ohms. Most of us would set a loudspeaker within 20 inches or so, which increases the level by 6dB, and, as I recall, the K3 has a 1 watt output stage. That puts a peak loudness of 91 dB in our ear for CW, and about 10dB less for SSB. 73, Jim Brown K9YC ______________________________________________________________ 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
