[Elecraft] K3 external speakers

[Jim Brown]

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