Re: KPA-1500 power reading?
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I trust my Bird 43 wattmeter that's in line with the amplifier output,
so I recalibrated the KPA-1500 wattmeter reading per band to correlate more closely with it. See WMTR ADJUST in the KPA-1500 menu. Jim W6YA ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [hidden email] |
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Trust the Wattmeter Only if it is seeing a 50 Ohm Dummy Load.
WA6VAB Ray From: Jim McCook Sent: Saturday, February 6, 2021 11:35 AM To: Elecraft Reflector Subject: Re: [Elecraft] KPA-1500 power reading? I trust my Bird 43 wattmeter that's in line with the amplifier output, so I recalibrated the KPA-1500 wattmeter reading per band to correlate more closely with it. See WMTR ADJUST in the KPA-1500 menu. Jim W6YA ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [hidden email] ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [hidden email] |
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On 2/6/2021 12:05 PM, Ray wrote:
> Trust the Wattmeter Only if it is seeing a 50 Ohm Dummy Load. Bird slugs have a tolerance of 5% of full scale, and the reading is only valid into a 50 ohm resistive load. The LP100A is 5% of the reading at any power level and into complex loads (i.e, not only 50 ohms resistive). Years ago, Electraft used an LP100A for final test of their rigs. Don't know if they still do. About five years ago, I bought W6OSP's LP100A from his estate and added a second coupler for my SO2R station, and had both calibrated at his factory. It auto-switches with signal from the amplifiers for the two radios. 73, Jim K9YC ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [hidden email] |
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In reply to this post by Jim McCook W6YA
Good points, Ray and Jim, I should have been more detailed with what I
posted. I checked The Bird 43 with two other Bird 2500w slugs from friends and they were all reading the same with a dummy load at 1500w. I did the KPA1500 calibration using the Bird with a high power dummy load, then checked again with my antennas in band segments where they present no significant reflected power and near 1:1 SWR. At those points they were in sync. Most of my antennas are flat on CW segments at specific spots without using the tuner in the KPA1500. I operate 99% CW and realize that when the load changes from 50 ohms the Bird reads wildly high and cannot be trusted. - Jim W6YA ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [hidden email] |
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The meter itself can be off too. Using more slugs does help things,
but to be really sure, test equipment needs to be periodically calibrated, which Hams never do. Dummy loads should be measured with a VNA. So, what you did is a big help, but still can't provide 100% assurance that it is accurate. I understand that is the best most Hams can do and probably better than most. An LP-100A does come with a NIST traceable calibration from the factory and it can be recalibrated, again something Hams never do. I have one fancy scope / spectrum analyzer that I do get calibrated yearly and I use that for a reference. I have a VNA with a set of calibration standards and use that to measure attenuators / taps that I put between my transmitter and the analyzer. I admit I do not calibrate anything else, but I use the calibrated stuff as transfer standards. I also have a couple GPSDOs as frequency standards to compare to. 73, Mark W7MLG On Sat, Feb 6, 2021 at 4:55 PM Jim McCook <[hidden email]> wrote: > > Good points, Ray and Jim, I should have been more detailed with what I > posted. I checked The Bird 43 with two other Bird 2500w slugs from > friends and they were all reading the same with a dummy load at 1500w. > I did the KPA1500 calibration using the Bird with a high power dummy > load, then checked again with my antennas in band segments where they > present no significant reflected power and near 1:1 SWR. At those > points they were in sync. Most of my antennas are flat on CW segments > at specific spots without using the tuner in the KPA1500. I operate 99% > CW and realize that when the load changes from 50 ohms the Bird reads > wildly high and cannot be trusted. - Jim W6YA > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[hidden email] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > Message delivered to [hidden email] Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [hidden email] |
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