OK, I guess I need to repeat what I said. The 25H is SPECIAL order from Radiodan W7RF <<mailto:rfpo...@radiodan.com>rfpo...@radiodan.com>, who has the ability to run NBS traceable calibration on these elements.
Any Bird element can be modified to a different power range (if you do a search you should find some sites that talk to this). But most of us do not want to dig into one that far. I think the wrong impression has been taken of Bird's statement of accuracy. I doubt the inaccuracy is a fixed amount that is the same at any reading. More likely Bird does its calibrations at full scale and this is the accuracy that they will warrantee. Seem more reasonable that the error is relative to the level of the reading. The actual adjustment is a variable cap inside the element. That and a resistor determine the level the element functions at. But that being said, I have no proof the element in question is any better than reading 25w +/- 1.25w. Ideally, I would have sent the meter to Radiodan to be calibrated with the element. Then he could have specified what the accuracy was for the calibration. But this is a brand-new element, freshly calibrated. Should I doubt it in favor of my 35 year old 100H element? Especially since resolution of reading 12w is much worse on the 100 scale than on the 25 scale. There is only one way for me to determine what the accuracy is. That is by observing the waveform across the dummy load with my scope, calculating Vrms from the peak-peak voltage and using that to determine power using V^2/R, assuming the load is not reactive. Well I might do that out of curiosity. That is probably the most accurate way for most hams to measure power (unless you are very rich and own a calorimeter). I did power measurement at 500-KHz by using my scope since I have no elements that work below 2-MHz. My 100w 500-KHz transmitter is equipped with an RF ammeter for measuring/monitoring power. For normal daily ham measurements I am willing to assume that the new element is my most accurate. Will it matter much if I am off 1.25w? BTW it could be better than that. That is the worse-case specification. 73, Ed - KL7UW, WD2XSH/45 ====================================== BP40IQ 500 KHz - 10-GHz www.kl7uw.com EME: 50-1.1kw?, 144-1.4kw, 432-QRT, 1296-?, 3400-? DUBUS Magazine USA Rep dubus...@gmail.com "Kits made by KL7UW" http://www.kl7uw.com/kits.htm ====================================== ______________________________________________________________ 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
