> If the onboard meter _thought_ the K3 was making the requested > power, that would be one thing. But in this case the onboard > meter thinks it's putting out 2x the power, which it is.
It depends on what part of the system thinks what. In this case the MCU is reading a given value but interpreting it as something else thanks to TXG VCE. TXG VCE does not effect the peak power in SSB or AFSK A with single tone modulation. It does effect peak power in DATA A. If you are seeing about 2x the power called for, decrease TXG VCE by 3 dB and see if the situation does not resolve itself (at the expense of power output in USB/LSB). Although the wattmeter is peak reading according to Wayne, TXG VCE still provides an inappropriate "adjustment." 73, ... Joe, W4TV > -----Original Message----- > From: Steve Ward [mailto:[email protected]] > Sent: Monday, January 05, 2009 3:38 AM > To: [email protected] > Subject: Re: [Elecraft] K3: Still unable to set power > correctly in, DATA A(sigh) > > > Joe, > > If the onboard meter _thought_ the K3 was making the requested power, > that would be one thing. But in this case the onboard meter > thinks it's > putting out 2x the power, which it is. So, I dial in 40w and > I get 80w > both by the internal meter and by my admittedly less than lab-quality > MFJ dummy load+meter. > > It did not do this before the most recent firmware. > Something got broken... > > 73, > > Steve AD7OG > > Joe Subich, W4TV wrote: > > > >> The point is it was providing the correct power output levels > >> before the last couple of firmware revisions. Something > >> changed that made it go from putting out approximately the > >> right power level, to putting out WAY TOO MUCH (i.e. causing > >> splatter) power. > >> > > > > Not true ... in spite of careful calibration at both 5 and 50 > > watt levels neither of my K3s has ever produced exactly the > > power requested on any band other than 20 meters, on any mode > > other than CW and at any power other than 5 or 50 watts. The > > variations can be as much as 3 dB on SSB depending on the peak > > to average ratio of the driving audio and amount of compression > > used. > > > > Setting a power control calibrated for CW and expecting that > > level to be accurate for PSK31 or any other arbitrary digital > > modulation is complete folly and utter hubris. Among other > > issues the wattmeter does not know if you are setting peak > > or average power and it does not know what the average power > > should be for the arbitrary data and arbitrary modulation. > > > > For the K3 to accurately control the power level in all modes > > the its directional coupler would probably need to be improved > > by at least an order or magnitude. The response flatness would > > need to be improved by at least an octave and the detectors would > > need to be substantially more linear ... and that's just for CW. > > To handle arbitrary audio inputs takes some knowledge of the > > peak to average ratio as well as the peak duration (duty cycle) > > in order to select the proper detector time constants. Every > > voice every digital mode and every arbitrary data stream will > > have different peak to average ratios and duty cycles. Do you > > expect the DSP to calculate those values on the fly? Perhaps > > the power metering should be derived from a DSP based spectrum > > analyzer? > > > > Accept the fact that the power level control is relative. If > > Wayne and Lyle can improve on it that's great. However, trying > > to hold .1 dB or even 1 dB accuracy from 1 mW to 120 W, 1.8 MHz > > to 54 MHz with arbitrary modulation sources in a reasonably > > priced amateur transceiver is a fool's errand. > > > > 73, > > > > ... Joe, W4TV > > > > > > > > > > > >> -----Original Message----- > >> From: [email protected] > >> [mailto:[email protected]] On Behalf Of Steve Ward > >> Sent: Saturday, January 03, 2009 2:54 PM > >> To: [email protected] > >> Subject: [Elecraft] K3: Still unable to set power correctly > >> in, DATA A(sigh) > >> > >> > >> "Joe Subich, W4TV" Wrote: > >> > >> > >>> So? Reduce the power you request to get the required > output. What > >>> other radio has a "calibrated" power output control? > >>> > >>> The wattmeter in the K3 is relative ... there is a > documented power > >>> vs. frequency slope. Testing seems to indicate there are also > >>> nonlinearities with changes in peak to average ratio and as the > >>> power level moves away from the calibration points. The > directional > >>> coupler in the K3 does not have the high level of directivity and > >>> compensation of a product like the Telepost LP-100 nor > does it have > >>> the high quality detectors. > >>> > >>> If you want a bloody laboratory grade meter, buy a > laboratory grade > >>> power meter. > >>> > >> The point is it was providing the correct power output levels > >> before the last couple of firmware revisions. Something > >> changed that made it go from putting out approximately the > >> right power level, to putting out WAY TOO MUCH (i.e. causing > >> splatter) power. > >> > >> Setting TXG VCE to -3 dB gets DATA A output almost to where > >> it should be, but of course adversely affects SSB. > >> > >> This is NOT about the accuracy of the wattmeter, its about > >> overdriving the PA. > >> > >> 73, > >> Steve > >> AD7OG > >> K3 #1544 > >> _______________________________________________ Elecraft mailing list Post to: [email protected] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
