I have just completed the Power Calibration (R26 andf R27) on my KPA100. The SWR shows 1.0-1 on 40 and 80M, but then goes up from there. It is 1.5-1 on 10m and power output as indicated on my external power meter shows power declining as the SWR is increasing. I am using an MJF 264 dummy load which is not the best. Any thoughts? Could I just be seeing a poor load?
Jonathan Gottlieb WA3WDK _______________________________________________ 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 |
Jonathan,
Those indications may be indeed correct. To properly answer the question, check your dummy load with an antenna analyzer first. 73, Don W3FPR > -----Original Message----- > > I have just completed the Power Calibration (R26 andf R27) on my > KPA100. The SWR shows 1.0-1 on 40 and 80M, but then goes up from > there. It is 1.5-1 on 10m and power output as indicated on my > external power meter shows power declining as the SWR is > increasing. I am using an MJF 264 dummy load which is not the > best. Any thoughts? Could I just be seeing a poor load? > > Jonathan Gottlieb > WA3WDK > No virus found in this outgoing message. Checked by AVG Anti-Virus. Version: 7.0.323 / Virus Database: 267.6.6 - Release Date: 6/8/2005 _______________________________________________ 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 |
In reply to this post by Gottlieb, Jonathan
It's possible that those indications are accurate and related, but not
necessarily so. Most wattmeters show total forward (including reflected) power, so if the reflected power goes up as the incident power goes down, the total remains the same. If your external wattmeter shows actual delivered power (forward minus reflected), then you would expect the displayed power to drop as SWR increases, although at 1.5:1 the effect would be minimal. It is more likely that the SWR increase you are seeing on your MFJ is real, and the lower power reading is just the KPA-100 delivering less power on 10m into the higher SWR. BTW, I have been doing a lot of work lately, along with a friend, to determine just how accurately power can be measured. We have determined that manufacturers' claims about absolute power measurement accuracy are extremely optimistic. We have access to tens of thousands of dollars of precision loads and measurement equipment, and find it terribly difficult to measure absolute power within .2dB accurately (~5%), and sticking a Bird 43 in line with typical ham dummy loads is definitely not the way. The Bird is a good example of misleading ratings. It is rated at 5% of full-scale with a high quality dummy load. In other words, if you had a dummy load with >40 dB return loss, the Bird would only be within 5% at full scale. At half-scale it would be 10% at best. And even if your load is 50 ohms exactly, the makeup of that 50 ohms plays a part... if part of the 50 ohm Z is reactance, the accuracy typically suffers as well. To make a long story short, I think most hams are lucky to have 10% accuracy, which is OK if you realize it. Larry N8LP Gottlieb, Jonathan wrote: >I have just completed the Power Calibration (R26 andf R27) on my KPA100. The SWR shows 1.0-1 on 40 and 80M, but then goes up from there. It is 1.5-1 on 10m and power output as indicated on my external power meter shows power declining as the SWR is increasing. I am using an MJF 264 dummy load which is not the best. Any thoughts? Could I just be seeing a poor load? > >Jonathan Gottlieb >WA3WDK > > >_______________________________________________ >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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