[Elecraft] K3 H Mode Mixer

[ik8tng]

Thank you very much for your comments.



Wayne recognized  interesting results when we reported yhe MDS, DR and IP3
comparison figures. We have to appreciate his comment “A few K3 users in
extremely high-signal environments might benefit   from a few extra dB of
dynamic range, at the cost of a mixer add-on  module like you described”,
this may reply to your question.



The K3 is a *high performance radio *and for this is very interesting. We
are *amateur radio *and we like to “squize” equipment to see if we can get
dome extra functionalities. With a radio like the K3 we cannot expect to
have improuvements of tens of dB/dBm, like it is possible with other
commercial equipment, following similar mods. As you can see we can still
squize out something. We are not doing business, only enjoying radio and we
like to share our findings with others Hams.



We went into the K3 1st mixer mod because it is really the easiest we can
apply to a radio…real swap with no soldering iron.   
http://elecraft.365791.n2.nabble.com/file/n6891521/hmodemixerelecraft.jpg  


We tried to measure spuries as suggested by Wayne but we were not sure about
differences. We decided to do other tests that may help to understand if the
improuvements are beneficial or not. Please see the second table figures.
The improuvements are not only instrumental but also detectable by ears. The
nearly 6dB in noise drop at the loudspeaker is something valuable and can be
felt.



K3 ORIGINAL MIXER AND 2T H-MODE MIXER COMPARISON



TABLE 1  Measurements 
RF in 14.220 MHz                             Original K3 Mixer originale          
2T H-Mode Mixer FSA3157 
MDS (Sensibilita’)                                  -126dBm                                    
-128dBm * 
Dynamic Range 2T                                    98dB                                       
101dB 
3rd Order Intercept IP3                            +21.0dBm                                 
+23.5dBm 

(*Audio Noise at output dropped <6dB)  
 
TABLE 2
Frequency RF in 14.220MHz               Original K3 Mixer originale           
2T H-Mode Mixer FSA3157 
RF in                                                        -40dBm                                   
-40dBm  
IF out 8.215 MHz                                        -44.5dBm                                
-44dBm 
30MHz noise level line                                  -80dBm                                    
-83dBm 
RF feedthrough/leakage                               -72.0dBm                              
Into the noise level
LO feedthrough/leakage 22.415MHz                -49.0dBm                               
-62.8dBm 
RF+LO 36.615MHz                                       -57.0dBm                                
-69.0dBm 
2xLO 44.830MHz feedthrough/leakage             -54.0dBm                                
-63.6dBm 
53.045MHz feedthrough/leakage                    -62.0dBm                              
Into the noise level


(The 2T H-Mode Mixer has a diplexer termination)


What else?....This is the spirit of amateur radio and nothing more
Saluti (73)

Sergio, IK8TNG
 

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