It's kinda' hard to beat numerical digits when you want the best possible resolution displayed. By the way Phil, I should re-phrase my earlier statement when I referred to a resolution "deficiency." I really meant to imply a resolution "limitation." There's nothing wrong with that form of wattmeter display, even with the set limitation on resolution. I prefer a bargraph display as a quick indicator of what's going on rather than interpolating quickly flashing numbers on a display.
Here's a link to N8LP's article in QEX. Accuracy is highly dependent on directional coupler design and construction technique as well as detector design. http://www.telepostinc.com/Files/phipps-1.pdf Paul, W9AC ----- Original Message ----- From: "Phil Hystad" <[email protected]> To: "Paul Christensen" <[email protected]> Cc: "Elecraft" <[email protected]> Sent: Wednesday, December 09, 2009 8:37 PM Subject: Re: [Elecraft] W2 Questions Paul, Thanks for your comments. And, in followup, if Elecraft were to make a meter with reasonably high accuracy I presume that another display method, other then LEDs, would be required. I think a high-resolution LCD with nice color graphic renditions of power information. OK, sort of kidding here, I presume that a computer interface could handle that kind of information display. peh On Dec 9, 2009, at 5:23 PM, Paul Christensen wrote: > Phil, > > With each LED representing 100-watts on the 2KW scale, it may be of some > help to go from 10% to 5% in accuracy, but in the case of the W2, the > display resolution is limited to 50-watts in between mid power ranges > (e.g., > 250-watts) but a display of 200-watts with two LEDs showing may actually > mean 151 watts or 249 watts. > > 50-watts is mid-way between any two LEDs at the 2KW range and I'm making > an > assumption that levels less than any 50-watt range (e.g., 240-watts) will > result in the preceding element being lit which shows 200-watts. If it's > more than the mid point (e.g., 260-watts) then the next LED should be lit. > So, at the low-end of the W2's range at say the 200-watt level, the meter > can at best resolve to only 50/200 = 25% and seemingly 100/200 = 50% at > worst (using the 149W to 249W example). I don't want to confuse > resolution > with accuracy but the two parameters go hand-in-hand. That said, I see no > real benefit of going from 10% to 5% in accuracy when resolution > deficiencies can easily mask the error in accuracy. I may be completely > wrong with the manner in which the W2 resolves, so someone set me straight > if my assumptions aren't correct. > > You asked the question about what it takes to achieve better accuracy. > You > may want to read N8LP's excellent article in QEX from a few years ago, > along > with articles from Warren Bruene, Roy Lewallen, John Grebenkemper, and > others who have published on the accuracy subject. > > Paul, W9AC > > > ----- Original Message ----- > From: "Phil Hystad" <[email protected]> > To: "Elecraft" <[email protected]> > Sent: Wednesday, December 09, 2009 7:51 PM > Subject: [Elecraft] W2 Questions > > >> A few questions about the W2 meter: >> >> 1. The posted accuracy is +- 0.5 dB which I calculate as about +- 12 %. >> Is this full scale accuracy and if so is half scale possibly more >> accurate >> or is this the most accurate the meter is likely to be. I am not even >> sure if it makes a difference for full scale or half scale for a digital >> meter so that part of my question may be moot. >> >> 2. What does it take to achieve an accuracy better then 5 % (for >> example), and is it possible to achieve an accuracy of 1 % or better? I >> am curious as to where the money needs to be spent in achieving such >> accuracy. Is it in the directional coupler? >> >> 3. I am thinking that the company that can build the best receiver on >> the >> market (the K3) can also build the best meter. So, would Elecraft >> principles consider a future super-accurate, best on the planet, amateur >> radio RF/SWR power meter? Oh, I think a current meter would be cool too. >> >> And, I know that having meter accuracy is of little importance in ham >> radio but there is some kind of deep seated quirk in me that wants >> accuracy just for the heck of it. Certainly 5 % is achievable, right? >> >> 73, >> phil, K7PEH >> ______________________________________________________________ >> 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 ______________________________________________________________ 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
