KAT2: SWR Accuracy
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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 _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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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" <[hidden email]> Sent: Tuesday, April 08, 2008 7:02 AM To: <[hidden email]> 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 > _______________________________________________ > Elecraft mailing list > Post to: [hidden email] > You must be a subscriber to post to the list. > Subscriber Info (Addr. Change, sub, unsub etc.): > http://mailman.qth.net/mailman/listinfo/elecraft > > Help: http://mailman.qth.net/subscribers.htm > Elecraft web page: http://www.elecraft.com > Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by Michael Linden
I found my WM-2 -very- difficult to calibrate accurately.
The pots are far too "touchy". Someday, I'll replace them with 10 or 20 turn Trimpots. I have several Birds w/50W elements and two Bird loads, but remember, their accuracy isn't what we all seem to think they are. I found the best accuracy came from using an Elecraft 50 ohm load and my DVM's voltmeter. Of course, the ultimate accuracy then becomes that of the DVM. Use -much- caution when using watt meters to calibrate RF-measuring devices. 73! Ken Kopp - K0PP [hidden email] _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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