Hi All, Over the years I've seen Bird Wattmeters for sale at dozens of hamfests, as well as over the internet. Typically these are very "pricey", and require all sorts of accessories. I have no doubt that this is, more or less, "the standard" when it comes to wattmeters. However, my question is (and I ask this seriously), just how often am I apt to really need something that is so precise? I have an Elecraft W1, and several other wattmeters around the shack, including an OHR W-1. I think the two I specifically mention are relatively accurate, although perhaps not quite up to "Bird" standards. All wattmeters need to be calibrated, and need to be re-calibrated if you change ranges significantly. To be honest with you, the only time I have any real concern about being 99.9% accurate is if I'm crowding the 5 watt limit in a contest. My solution is to just set it for 4.5 watts, and my conscience is clear! Otherwise, whether it's 5 watts vs. 5.2 watts, or 100 watts vs. 101 watts, doesn't seem to make much difference. Should I care????
Dave W7AQK ----- Original Message ----- From: "Ron D'Eau Claire" <[email protected]> To: <[email protected]> Sent: Friday, May 29, 2009 9:10 AM Subject: Re: [Elecraft] K3 Watt-meter question! > 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 > ______________________________________________________________ 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
