Thanks Bob, Yet another variable! I just measured my dummy load at 54 ohms (cold). Maybe I should just declare victory and move on!
73, Jim KO5V -----Original Message----- >From: Bob McGraw K4TAX <rmcg...@blomand.net> >Sent: Nov 9, 2018 8:51 PM >To: Jim KO5V <k...@earthlink.net>, donw...@embarqmail.com, Elecraft List ><elecraft@mailman.qth.net> >Subject: Re: [Elecraft] K2: KPA100 fan issue + current question > >Not at all unusual for the currents to be different on different bands. > >Since most power meters are voltage sensing devices, the value of the >dummy load will affect the power indication. Thus as the R value >increases the voltage across the R increases for a given power value and >thus the meter will indicate more power than actually exists. And the >better power meters are typically +/- 5% full scale, i.e. Bird 43. >Many ham meters are +/- 10%. The LP-100 is +/- 3% with NIST factory >calibration. > >As to dummy loads, I have 3 and they all say 50 ohms on the label. In >fact they measure between 48 ohms and 54 ohms when cold. The value goes >up as the element and radiator heats. While that's not much, in fact >it is approaching 10%. That throws another variable in power >measurements. > >I stopped frettin' over power values a long long time ago. > >73 >Bob, K4TAX > > > >On 11/9/2018 4:56 PM, Jim KO5V wrote: >> Don and Bob, >> >> The K2 and amp are both powered from the amp's supply. >> >> I used a known good DVM to measure the voltage across R7, and it agrees with >> old Beckman. I now think my old kit-built Ten Tec power meter may be badly >> out of calibration. I have a dead LP-100 that is on its way back to Larry >> for upgrade and calibration, so I'll just wait until it is back to finish >> calibrating the KPA's power setting. >> >> Here are what I measured and calculated at the approximate center of each >> band, in cw, when the K2's LCD read 100W: >> >> 10M: .067V, 13.4A >> 12M: .049V, 9.8A >> 15M: .064V, 12.8A >> 17M: .065V, 13A >> 20M: .048V, 9.6A >> 30M: .056V, 11.2A >> 40M: .052V, 10.4A >> 60M: .056V, 11.2A >> 80M: .054V, 10.8A >> >> The current seems to vary significantly between bands, but maybe that's >> normal? >> >> Thanks again. 73, >> >> Jim KO5V >> >> >> >> -----Original Message----- >>> From: Don Wilhelm <donw...@embarqmail.com> >>> Sent: Nov 9, 2018 11:37 AM >>> To: Jim KO5V <k...@earthlink.net>, Bob McGraw K4TAX <rmcg...@blomand.net>, >>> Elecraft List <elecraft@mailman.qth.net> >>> Subject: Re: [Elecraft] K2: KPA100 fan issue + current question >>> >>> Jim, >>> >>> That 11 amps would sound more reasonable to me if you can say that the >>> base K2 is being powered separately, but I would expect something closer >>> to 50% efficiency rather than 66%. >>> >>> 73, >>> Don W3FPR >>> >>> On 11/9/2018 12:42 PM, Jim KO5V wrote: >>>> Thanks Bob, >>>> >>>> That makes me feel a bit better. I'm still going to remeasure it with a >>>> newer meter and see if the measurements check. >>>> >>>> 73, Jim KO5V >>>> >>>> >>>> -----Original Message----- >>>>> From: Bob McGraw K4TAX <rmcg...@blomand.net> >>>>> Sent: Nov 9, 2018 10:29 AM >>>>> To: Jim KO5V <k...@earthlink.net> >>>>> Cc: Elecraft List <elecraft@mailman.qth.net> >>>>> Subject: Re: [Elecraft] K2: KPA100 fan issue + current question >>>>> >>>>> At 13.8 volts, 11amps is about 152 watts input. 100/152 = .658 * 100 for >>>>> about 66% efficiency. >>>>> >>>>> All in all , looks about right to me. AKA - I wouldn't be concerned. >>>>> >>>>> >>>>> Bob, K4TAX >>>>> >>>>> > > ______________________________________________________________ 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
