The original military specification document, to which the bird43 was built only requires 10% accuracy (to accomodate "field usage"?)
I did some checking with a power attenuator and an hp436 power meter my k3 power meter agrees within 1% on the hf bands with the same 100H element in 2 different bird "bodies" i see errors of +3% and -4% Dave ww2r ---------------------------------------------------------------------- Message: 1 Date: Fri, 29 May 2009 09:10:56 -0700 From: "Ron D'Eau Claire" <[email protected]> Subject: Re: [Elecraft] K3 Watt-meter question! To: <[email protected]> Message-ID: <001001c9e078$0f538940$2dfa9b...@biz> Content-Type: text/plain; charset="us-ascii" Jim, you said "supposedly accurate". A Bird wattmeter is accurate only if it's been properly calibrated and handled carefully - especially the "slugs". Bumps and bangs can easily ruin the calibration (That's why all Birds used in critical applications carry calibration stickers showing when it was last checked - normally no less often than annually - and is carefully handled and stored in approved containers). Let's assume the Bird is recently calibrated and treated kindly: 1) Its calibration is then dependent upon using the right slug. You probably know better, but a surprising number of Bird owners think the frequency range on the slug isn't very important. I believe the proper Bird 43 element for 6 meters is the type A slug spec'd for 25-60 MHz. 2) Are you allowing for the normal error in even a perfectly-calibrated Bird? That's +/- 5% of *full scale*. IIRC the Bird 6 meter slugs have full scale ranges of 25 or 250 watts. If you're measuring 100 watts with the 250 watt slug, the possible error in a properly-calibrated Bird is +/- 5% of 250 watts *anywhere* in the scale. So at 100 watts indicated, the actual power may be anywhere between 87 and 112 watts. That's plenty good enough accuracy for nearly all field use, including for showing that transmitter power levels comply with FCC regs (although when I demonstrate a marine transmitter to FCC engineers, it's *their* Bird that is the final word ;-) Now, the K3 has simply another wattmeter built in, so it's normal for the two wattmeters to disagree by the sum of their possible errors. You asked, "Which one is more accurate?" One of the Elecraft engineers would have to answer that, but let's assume the K3's built in wattmeter is as good as the Bird. In that case a perfectly calibrated Bird on a perfectly calibrated K3 may disagree by as much as 15 watts at 100 watts giving you an indication of anywhere between 85 and 115 watts on the Bird when the K3 meter says 100 watts. And don't forget that assumes everything is in perfect calibration. In the real world, it's not unusual to see a greater error. That's why it's not normally considered important for owners to worry about the K3's power calibration. Unless you have some laboratory standards to compare to each other and to the K3, it's almost impossible to improve on the default factory settings. Ron AC7AC -----Original Message----- Gentlemen, How accurate is the built-in watt meter indicator in the K3??? I'm asking because when I've used a supposed;y accurate "Bird 43" while measuring the K3's various outputs on the various HF bands there seems to be a slight discrepitancy between what the K3 is showing and what's actually there according to the "BIRD!!!" I'm particularly interested in the output readings as concerns "6 metres!" Which is MORE ACCURATE??? Regards, Jim/nn6ee S/N 2406 ______________________________________________________________ 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
