[Elecraft] K3 6/10M pre-amp

[Edward R Cole]

Been a lot of discussion on this topic so I decided to make some 
"real" MDS measurements comparing my K3/10 (4340) and KX3 (475).  I 
hope the columns read clear for everyone (I can create some charts on 
my website, if not):

Test set up:  XG3 + JFW 30-dB step attenuator + 6-inch of RG-58 w/BNC's
The XG3 is installed in a Hammond "diecast aluminum" enclosure with 
BNC feedthru adapter so the unit is fully shielded (I have made MDS 
measurements using additional 20-dB coaxial attenuator to -157 dBm 
+/- 2 dB.  That was using double-shielded coax whereas today's tests 
were using ordinary RG-58 (so adds a little uncertainty on the 
minimum signal).  MDS detector are my "ears" so that makes a bit more 
subjective for absolute measurements.

Both radios tuned with 2.8 KHz bw in USB, Elecraft's MDS spec is done 
at bw = 500-Hz.

50.120 MHz
Level (dBm)     K3+PRE         KX3+PRE(30-dB)     K3 (no preamp)
XG3 off            S1                  S0                          S0
-73                  S9+5              S9                          S8
-107                S3                  S4
-123                ---                   S1/S2
-130                S1                   below MDS
ANT                S2                   S2/S3                    S0 
(slight rise in noise in speaker)

28.200 MHz
Level (dBm)      K3+PRE        KX3+PRE(30-dB)
XG3 off             S1                 S0
-73                   S9+5             S9
-107                  S4                S3
-123                  ---                 S0
-133                  S1                 Below MDS

I also checked frequency using the K3 as reference (has EXREF) and 
the KX3 was 50-Hz higher than the K3 on 6m and 40-Hz higher on 10m (I 
have not done the temperature calibration for the KX3).  I did not 
measure freq drift after transmitting.

One would state that the K3 looks better than the KX3 for receiver 
sensitivity (yet the KX3 hears 6m much better - hmmm?)

73, Ed - KL7UW
http://www.kl7uw.com
dubususa at gmail.com
"Kits made by KL7UW"