Hi
Your numbers look normal to me. You may be able to improve the calibration
using a 100 and 25 ohm load. This is how I do the calibration.
First get it into the ball park with the manual calibration method
Then alternate with the 100 and 25 ohm load and adjust C55 to get the same
reverse reading
Increase the reverse pot to indicate 2.0 SWR and check at both loads for the
same reading tweak C55 if needed
Go back and adjust the forward power to agree with your external calibrated
meter with a 50 ohm load
Check the 25 and 100 ohm SWR readings again for a 2.0 value. The forward and
reverse settings will interact so you may need to do all of the above
several times to get it set up correctly.
Your loads should not have cables connected to them. They should connect
directly to the tuner connectors. I built my loads into standard UHF
connectors (PL-239) and use BNC adapters for the KAT2 or directly for the
KAT100. I used two 51 ohm in parallel for the 25 ohm, one 100 ohm for the
100 ohm load and two 100 ohm resistors in parallel for the 50 ohm load. The
resistors are 2 and 5 watt MOS types and mounted inside the connector. It is
OK to use a cable with the 50 ohm load when using the WM-2 but as a final
check I connect the 50 ohm load directly to the KAT2 and check for a 1.0:1
reading
Thanks
Don Brown
KD5NDB
K3 S/N 0575
--------------------------------------------------
From: "Michael Linden" <[EMAIL PROTECTED]>
Sent: Tuesday, April 08, 2008 7:02 AM
To: <elecraft@mailman.qth.net>
Subject: [Elecraft] KAT2: SWR Accuracy
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
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