[Elecraft] KAT2: SWR Accuracy

[Michael Linden]

  I've just completed alignement of my KAT2 and am a bit dismayed by its SWR accuracy.
   
    I feel pretty confident that I found the true dip in C55 at a value of 12. I then aligned the forward power (R1) using an OHR WM-2 that was aligned on 40m against test equipment. The 50 Ohm dummy load I'm using reads a flat 1.0:1 up into the 2m region on an MFJ-259B. I'm fairly happy with the forward calibration which yielded the following results:
   
  BAND  K2    WM-2
  160      4.4   5.0
  80        4.6   5.0
  40        4.9   5.0
  30        5.2   5.0
  20        4.9   4.9
  17        5.0   5.0
  15        5.1   4.9
  12        5.5   5.0
  10        5.6   5.0
   
    I initially calibrated reflected power (R2) by measuring the wiper-to-ground resistance on R1 and setting R2 for the same wiper-go-ground resistance. The reflected calibration results range from 1.0:1 on 160m to 1.2:1 on 10m into the 50 Ohm dummy load. However, the SWR readings I see when using a 25 Ohm dummy load (confirmed on MFJ-259B) aren't very good. The KAT2's 25 Ohm dummy load readings range from 1.7:1 on 160m to 1.2:1 on 10m.
   
    Given the preceding results, I decided to set the reflected adjustment (R2) to show 2.0:1 on 40m into the 25 Ohm dummy load. This time, the results varied from 2.1:1 on 160m to 1.3:1 on 10m. I have considered going back and readjusting R2 to show an average reading of 2.0:1 across the bands into the 25 Ohm load (higher than 2.0:1 on 160m, lower than 2.0:1 on 10m -- a compromise).
   
    Is the accuracy displayed above typical of the KAT2? If not, maybe I need to go back and reevaluate my C55 calibration (although I felt pretty confident that it is correct).
   
    Thanks, Michael N9BDF, K2 #4137