[Elecraft] Understanding the KX3 Block Diagram

[Mike WA8BXN]

Hi Dave, 
 
I'll try to give you some perspective on it. First, have you used a direct
conversion receiver? If they are decently designed, you don't get much
problem from out of band signals. The problem is selectivity. You can use an
audio filter, but they don't do anything for opposite sideband rejection.
You hear each signal above and below zero beat. 
 
Now add that back end you mention. There is so much "magic" that can be done
there. Of course, its not really magic. Its digital signal processing. Its
not like an analog audio filter. Coming out of the detector there are two
audio signals, referred to as I and Q. Software is able to use those two
audio signals to get opposite sideband rejection.That is accomplished by
digital methods much like SSB generation using the phasing method if you
understand that. Also very sharp filtering can be done, in effect somewhat
like audio filtering. Other processing can be done including carrier nulling
(useful on SSB when someone is tuning up) and noise reduction. 
 
Bottom line, its a very sound way to implement a rig these days. 
 
73 - Mike WA8BXN 
 
 
 
-------Original Message------- 
 
From: David Stratton 
Date: 3/7/2012 10:20:05 PM 
To: Elecraft Reflector 
Subject: [Elecraft] Understanding the KX3 Block Diagram 
 
Hoping that I may not be the only Ham puzzled by the block diagram of the 
KX3 I am asking that someone please explain it because it is so different 
>From the superheterodyne radio concept I have become accustomed to in 
Current amateur radios. I understand direct conversion radios but what is 
All the stuff that's there besides the mixer-oscillator and audio amplifier 
Needed by a direct conversion radio? It seems to me the KX3 block diagram 
Looks a lot like radios put forth some time ago by Rick Campell KK7B. Pardon

My saying so but the KX3 radio looks like it has a weak front end and a 
Heavy back end that hopes to make up for the weak front end! 
 
Dave - KO4KL 
 
 
 
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