Hi Jack and Don, As Ron says, VFWD and VRFL are related to forward and reflected power. Actually, they are roughly proportional to forward and reflected *voltage*. I say roughly because there is some nonlinearity from the rectifier diodes, especially at low power. The constant of proportionality is somewhat dependent on frequency, power level *and * has some unit to unit variability. That's the stated reason why Elecraft chose not to make any estimation of actual power levels. But SWR is easily calculated b y the formula:
VSWR = (VFWD+VRFL) / (VFWD-VRFL) This formula factors out all the variability mentioned above except the diode nonlinearity. In your case this works out as (225+3) / (225-3) = 1.03 Since SWR is all that is required to be known in an autotuner, that's all the KAT500 is calculating. Actually the calculated SWR doesn't even have to be very accurate as long is it a monotonic function (no dips or peaks) of the actual SWR. To be fair, the KAT500 does need an estimate of forward power since that is being used to fault if it is too high, but it doesn't have to very accurate. The forward power is proportional to VFWD squared. AB2TC - Knut Don Wilhelm wrote > Jack, > > For any wattmeter (the one in the KAT500 included), the VFWD and VRFL > values are related to forward power and reflected power. Those are raw > numbers and some math is required to calculate the actual power and SWR. > > VRFL subtracted from VFWD can be used to computer the power into the > load (in this case the input to the KAT500), but you need to know the > scaling factor that may be unique to the wattmeter. > > Similarly, if you divide VRFL by VFWD, you will obtain a result that is > related to the SWR. > > See the formulas associated with SWR in most any book dealing with > antennas and transmission lines. > > 73, > Don W3FPR > > On 1/11/2018 7:07 AM, Jack Satterfield wrote: >> Can someone explain the VFWD and VRFL readings in the bottom right of >> screen? >> >> When I put out a 15w tune signal, VFWD reads 225 and VRFL reads 2 to 3 >> >> Just trying to make sense of the readings >> >> >> >> Jack >> >> W4GRJ >> >> >> >> ______________________________________________________________ >> Elecraft mailing list >> Home: http://mailman.qth.net/mailman/listinfo/elecraft >> Help: http://mailman.qth.net/mmfaq.htm >> Post: mailto: > Elecraft@.qth >> >> This list hosted by: http://www.qsl.net >> Please help support this email list: http://www.qsl.net/donate.html >> Message delivered to > donwilh@ >> > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto: > Elecraft@.qth > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > Message delivered to > lists+1215531472858-365791@.nabble -- Sent from: http://elecraft.365791.n2.nabble.com/ ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
