Carl, You may want to re-calibrate your KPA100 wattmeter (and also check the calibration of your other meters). If you have a good non-reactive dummy load, it is really easy, but check your dummy load with an antenna analyzer first to be certain that it will do th ejob properly at the frequency where you will do the calibration.
Wattmeter calibration is a subject for extended discussion - just be aware that no matter what the advertizement implies, many wattmeters can be off by a great deal. Look at the specs and you will normally see something like +/-10% of full scale - what that means is on a 200 watt scale, the reading can be off by as much as 40 watts!!! and that applies to the entire scale too, not just the upper end. Most are not really that bad, but some are, and SWR can be proportionally incorrect. I calibrate the forward power in a wattmeter by driving a non-reactive 50 ohm dummy load and measuring the RF Voltage across that load - my calculator then tells me what the K2 display should be showing for forward power - adjust until it agrees with the actual power calculated. I would be willing to wager that the resulting setting will be as accurate as the best external wattmeter you can find on the ham market (Bird included). After setting the forward power, I calibrate SWR on the KPA100, KAT2 and KAT100 wattmeters with my pair of 2:1 SWR dummy loads - I have a non-reactive 25 ohm dummy load and a 100 ohm dummy load. I switch between them and to check the null capacitor adjustment first, the SWR reading should be the same for both loads - if not, I adjust it slightly until it is the same - then I set the REF pot so the K2 displays the SWR as 2.0. This method works fine, and I believe it was first suggested by Don Brown. The settings for the KPA100 and KAT100 will not be veery far away from th einitial setting suggested in the manual, but for some reason that I have yet to explain, every KAT2 requires that the REF pot be set much higher than the FWD pot to achieve a 2:1 display with the SWR=2 loads. Since the KPA100 reduces power when an SWR>2 is encountered, it is informative to know when that is likely to happen and take steps to avoid it. 73, Don W3FPR > -----Original Message----- > > My K2/100, SN 3777 works great. No complaints > > However, I am a bit leery of the indicated SWR. > > The indicated SWR seems to tell me that my antenna match is better in > nearly all cases than several other SWR and power meters I have > laying around. > > When SWR is measured using a MFJ 962 tuner, a Daiwa 101N meter, a Bird > 43, Autek RF-1, or a MFJ 249 analyzer, the indicated SWR is always higher > than that shown on the K2. > > For example, pressing TUNE on the K2 may indicate a 1.0:1, but the other > meters all consistently indicate a value significantly higher - lets > say 1.4:1 > > If I happily ignore the other SWR measurement tools, and only use the K2 > SWR indications, everything still works great, I make lotsa contacts and > all is well. > > However, at the home QTH, I do have a fairly well matched antenna, and I > do know that it is resonant in the band segments that I work. > > Taking he K2 into the field is another question altogether. At this > point, I don't trust the K2 SWR readings and have been dragging along > other SWR meters when loading a temporary or unknown antenna. > > Please advise. > > Carl > WA7CS > > _______________________________________________ Elecraft mailing list Post to: Elecraft@mailman.qth.net 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
