Comparing your S meter lights on the K3 with the P3 is comparing a length measured with your shoes with a length measured with a measuring tape, and that should include the fact that your left shoe is size 6 and your right shoe size 5, as S9 and down are 6 db increments and all above are 5 db. And just how much accuracy would one really be looking for in a 1.25 inch segment display that covers 108 dB.
If this were put on an analog meter with the same length of display which by some miracle were driven with a perfectly linear circuit, the needle would be 2 or 3 dB wide on the scale, not to mention parallax error. If you are properly calibrated on the K3, the S9 light will be turned on if the signal is anywhere between -73.0 dBm (when the S9 segment comes on) and -62.1 dBm (when the +5 segment comes on). The light should mean anything at least S9 but less than 5 over. When I calibrated mine carefully I was able to have the correct light come on in the correct dB advancing a precision attenuator dB by dB. The tenth of a dB spot wandered around a bit. This makes the segment display more accurate than the fictitious (and unattainable) analog meter above, if one ignores the fact that the segment display is "blind" for 4 or 5 dB spots between the flip points. There is a distinct usefulness to knowing the absolute noise level, and whether a signal is in fact 40 over 9, no kidding, no sh*t. Most people clearly and consistently recognize sound level changes at 3 to 6 dB levels, and 5 or 6 dB increments is a nice match to this general heel-to-toe order of magnitude scale. It's as accurate as measure by counting strides, which one relative can get to within a yard or two across the length of a football field. When I9*** is 40 over 9 on a calibrated K3 S meter, meaning his signal is -33 dBm, regardless of how good the 5 element 40m quad is, I know that he's as loud as the BC stations up above 7.2 MHz, and his power for the contest is the majority of his power bill for the month. I don't own one, but I believe that the W2 has the cute extension to the LED display of coming on weakly as the segments are crossed increasing to full brilliance as the next segment value is approached, which if that were possible on an LCD display would give the display perhaps 2 dB accuracy presuming the operator would perceive low, medium and high brightness. But this would only remove the blind spots between the flip points. The K3 S meter is an "order of magnitude" measure-by-stride indicator. The P3 is a ruler where you can see less than 1 dB increments on signals. 73, Guy. > Let's say you calibrated your S-meter to read S9 with a 50 uV input > signal. Fifty microvolts is -73 dBm in 50 ohms. > > A CW signal which is S9 on your S-meter should peak at around -73 dBm (plus or > minus 3 dB) on the P3. But an SSB signal which is S9 on your S-meter will not. > It will be several dB less than -73 dBm on the screen of the P3. Why? > ______________________________________________________________ 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
