On 8/6/2013 5:51 AM, Lyle Johnson wrote:
It is always best to use headphones or external speakers that have limited response above 5 kHz with the KX3. The radio will not pass audio information above this frequency, so the only thing wide response headphones or speakers will provide is additional noise.
Horsepucky. This is nothing more than an excuse for poor design. There are several possible solutions, perhaps in combination, but using lousy headphones or speakers is not one of them -- headphones and speakers with poor HF response are also likely to have very bumpy amplitude and phase response in midrange.
First, the audio bandwidth ought to be limited in the radio -- a few poles of low pass around 6 kHz would make a nice dent at 12 kHz. Second, if there's that much ripple, it sure sounds to me like the power supply is either inadequately filtered or poorly regulated, or there's insufficient decoupling somewhere in the audio chain.
Or perhaps even a circuit layout issue. On several occasions, I've urged the Elecraft engineering team to attend one of Henry Ott's excellent EMC workshops. Henry talks about keeping track of where the current is flowing -- ALL of the current, not just the "intended" current, and he talks about the invisible schematic hidden behind the "ground" symbol, which is one of the most common ways we lose track of the return current. If, for example, the current associated with that 12 kHz clock happens to share a return current path with an audio gain stage, it gets added to the audio. It's the same sort of mechanism that if it's at the junction of the box and the outside world we call a "Pin One Problem."
73, Jim 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
