[Elecraft] K3: LPF, bass audio, new DSP board: Stirring the pot?

[Jim Brown]

On Mon, 28 Dec 2009 21:09:46 -0500, DOUGLAS ZWIEBEL wrote:

Your post is excellent, and I agree with most of it. I do want to 
correct an important error. See below. 

>If the "noise" is not due to intermod (what Elecraft calls 
>"desense") 

Intermod and desense are VERY different things. Intermod is the 
generation of beat frequencies by a non-linear process (that is, 
amplitude distortion). Desense (short for desensitization) is the 
reduction in the gain of a system by such severe rectification of 
the input signal that the bias point is shifted enough (to either 
cutoff or saturation) to reduce the gain of the system. 

Yes, both are the result of overloading of a gain stage (usually 
the input), intermod simply produces trash and spurious responses, 
while desense can literally turn the input stage off. As an 
example, I once owned a very nice little Yaesu talkie that could 
be biased so strongly into cutoff in downtown Chicago that it 
couldn't hear a 100W repeater feeding a 9dB gain antenna on a 
1,000 ft building two miles away. 

>then what can cutting back on the
>total signal due in terms of making "less noise?"

EXACTLY! The vast majority of HF communications circuits are 
limited by noise that comes in on the antenna, not circuit noise 
in the receiver. This is definitely true on all ham bands below 
20M, no matter where you live, and it's usually true above 20M 
unless either the bands are dead or you live in a VERY quiet QTH. 
W8JI has often observed that if the noise in your headphones 
increases when you connect the antenna, noise in the electronics 
is NOT a problem. 

FWIW, I have ALWAYS used pro quality headphones with my ham gear, 
and certainly don't consider the K3 noisy. Of course, I'm 68, have 
been a ham for 54 years, and have worked in pro audio for the past 
40 years, so my hearing is down a bit on the high end. :)  YMMV. 

It should also be noted that while the K3 comes with multiband 
graphic RX EQ, there are no bands above 5kHz. That's something 
that the crew in Aptos might want to add to the "to do" list.  

73,

Jim K9YC