I've been reading the comments about Bird43 accuracy for awhile, but the claim that the error is fixed amount for all levels of power measured on a given element just does not agree with my experience. (Just about) ALL of my RF power measurements have been using the Bird and what I see is a scaled error and not a fixed one. If the full scale reading is off 5% then the quarter power is likewise 5% off. In other words 100w measured with a 100E element at 432-MHz might actually be 95w. If I measure 50w with the same element the actual power will be about 47.5w. 25w will be about 24w. I'm not saying the accuracy tracts exactly linearly with power level but it seems approximately so.
That being said, the accuracy for measurements at under 25% of the full power rating of the element is not of much value except as a relative number. I try to chose an element so the meter reads >70% full scale for best accuracy and resolution if I am trying to obtain absolute power measurements. If I want better accuracy I use calibrated attenuators with my HP432A microwave power meter (10-MHz-18-GHz) which measures -20 to +10 dBm. I have two high-power 20-dB coax attenuators: 100w NARDA (good to 4-GHz) and 10w Bird (good to 1-GHz). I measured the Bird on a steady 2m signal yesterday and it is exactly 20 dB within the 0.2 dB resolution of the HP meter. For measuring 300w on 1296 I have some 40 and 50-dB directional couplers from the cellular industry (rated for high power). That permits power measurements to be made with the HP power meter (300w = +55 dBm => -50 dB = +5 dBm) 2:1 SWR reflected power would be 30w (+ 45 dBm +> -40dB = +5 dBm). But this also allows me to check the accuracy of the Bird power meter. I suspect this is "good enough" for ham radio purposes. 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 [email protected] ====================================== ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
