Jim, Being one not to trust any instrument until it has proven its worth (and calibration), I would not trust either until calibrated.
OK, that brings up the question of how to do a meaningful calibration. I connect to a known good (precision) 50 ohm dummy load, and read the RF voltage at the dummy load with my oscilloscope equipped with an RF Probe. A coax TEE adapter placed at the dummy load will give you access to the center conductor. Make certain the 'scope and probe are rated for greater than 5 times the frequency at which you are doing the measurement. A quick and easy formula is to measure the peak to peak RF voltage, square it and divide by 400. Quicker and more accurate than doing conversion to RMS and then calculating - a lot of terms cancel out if you want to attempt to derive my formula yourself. Note that many analog wattmeters are only spec'ed for 20% of the full scale reading. On a 200 watt scale, that means it can be off by 40 watts at any point on the dial. Even the much revered Bird wattmeter is only to be trusted to 5% of the full scale reading, and that is only after lab calibration - so with a 100 watt slug, even the Bird can be in error by as much as 5 watts at any point on the scale. The precision dummy load and the 'scope can do 5% or better at the level being measured - i.e. at 5 watts, you may have a 0.25 watt error, and at 50 watts you may have a 2.5 watt error, but that is much better than a typical analog wattmeter. 73, Don W3FPR On 9/18/2011 8:58 AM, k2z...@aol.com wrote: > Hi, > > > > My KPA-500 watt meter and my Palstar watt meter read about the same at the > higher power readings. But at the 100 watt and lower ranges there is a > significant difference. My question is which is the more correct reading at > the lower ranges, the Elecraft or Palstar. If I want to calibrate my K3 which > one would be more accurate? Being that the Elecraft is a digital display > would that one be more accurate? > > > Thanks, > Jim Douglas K2ZF > > > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:Elecraft@mailman.qth.net > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
