KL7UW wrote: > 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.
The manufacturer's accuracy specification is what it is...not what you might think is "reasonable". Most analog meters are calibrated in % full scale due to the inherent error in visually interpreting a needle on an analog scale. This visual error is constant at all readings, hence the specification is a percentage of full scale. This is exactly why DMMs replaced analog meters (e.g. Simpson, Triplett, etc) decades ago. > 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. The LP-100A is factory calibrated (NIST traceable in 11 frequency bands) to 5% of reading (3% typical). As stated before, the key difference with the analog Bird is that accuracy is specified in % of reading...not % of full 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. This is essentially what the LP-100A does using an A/D converter and microprocessor. Besides being much more accurate, it provides many other useful features such as Z, R, X, SWR, SWR and phase versus frequency, Smith Chart output, translates coupler load Z to antenna load Z (for remote measurements), peak-to-average (useful for measuring SSB compression), etc. Measurement range is 1-3000 Watts over 1.8-54 MHz with the standard coupler (higher power available as options) at full rated accuracy. > 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. I can understand being locked in to Bird because of your significant investment in 16 slugs (typically $60-80 each on eBay not counting the Bird 43 itself). However, for anyone considering a truly state-of-the art Wattmeter, it's hard to beat N8LP's LP-100A because it does so much more than simply measuring power. If you add up the total cost of a Bird plus multiple slugs to cover the same power ranges, the LP-100A is a steal. Like all of Larry's products (LP-PAN, LP-Bridge, etc) the engineering and support for the LP-100A is first rate (e.g. providing a customer upgrade path from the original LP-100 to the LP-100A). http://www.telepostinc.com/ I have no connection with Larry other than being a very satisfied customer with several of his products. 73, Bill W4ZV -- View this message in context: http://elecraft.365791.n2.nabble.com/KX3-and-Data-modes-tp7368721p7371630.html Sent from the Elecraft mailing list archive at Nabble.com. ______________________________________________________________ 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
