You CAN NOT make those tests at 50 Watts! The power calibration circuitry will be constantly changing the internal gain. If the ATU is enabled and/or your dummy load is not flat the changes invalidate the measurements.
Further, single tone power calibration is only accurate for the specific frequency within the IF filter on which the calibration is performed. If I calibrate power in CW mode that calibration point is approximately 300 Hz from one "corner" of the 2.8 KHz filter thanks to the way the K3 offsets the filters. When I switch to DATA A, and try to test the power level with a 1500 Hz tone, I can see 2 dB more power simply because my 2.8 KHz filter has a 4 dB slope across the passband and the K3 gain calculation includes compensation for the loss at the calibration frequency. If I check the power with a 1 KHz tone, the difference may be 3 dB (DATA A is USB, CW calibration is LSB so the slope changes direction with tone). If I switch to AFSK A (REV to stay with USB) and check power with a 2295 Hz (USB Mark) tone, the difference may be down to one dB or so. There are too many uncompensated variables to expect the K3 to maintain absolute control over the power output with changing antennas, power levels, modes, (relative) frequency within the IF passband and possibly even different filters. ALC controls the audio level into, and the RF level out of the DSP (modulator) process - it is an ALC (automatic LEVEL control) NOT an APC (automatic POWER control). The ALC is an open loop system - the loop gain is calibrated once at the 5 watt level and once at the 50 watt level for one specific frequency in the IF passband. Once that is done, ALC simply controls the DSP gain. If you change the system gain following the DSP, the output power level WILL CHANGE. I'm sure it would be theoretically possible to calibrate the system gain from 100 Hz to 2900 Hz offsets from the carrier (for both the USB and LSB cases) and apply that mask to the modulation process but does the DSP system have enough horsepower to do so and is it worthwhile simply so the operator can avoid the need to check his power level when changing mode or modulating frequency? 73, ... Joe, W4TV > -----Original Message----- > From: [email protected] > [mailto:[email protected]] On Behalf Of Julian, G4ILO > Sent: Saturday, February 14, 2009 11:58 AM > To: [email protected] > Subject: Re: [Elecraft] K3 Beta firmware rev. 2.82 > > > > > Steven.Zabarnick wrote: > > > > > > I installed the new beta last and tested the new output > power control. > > I don't see any improvement in PSK31 output power using > DATA A mode. I > > still get nearly twice the output power than I have dialed > in by the > > PWR knob. In the previous firmware, the measure output power in CW > > modes agreed with the > > PWR knob setting, but now the power output in CW is 20-30% > higher than the > > setting. > > > > I will try to redo the transmitter gain calibration to see if this > > helps. > > > > > I have just got round to testing this firmware release. > Before testing the power output in DATA A mode I did a power > calibration. > > It seems to me that there is still something wrong with the > power control in DATA A mode. To make a comparison, I > switched the input for SSB to LINE IN so I could compare the > power output when sending a pure tone in both modes. > > In DATA A the gain seems to have been reduced, and I had to > increase the LINE IN setting. With PWR set to 50W and the > input level set to give a steady 4 bars, I measured 80W on my > power meter. A slight improvement but still not enough. > > In SSB the power output was correctly controlled so that only > 50W output was produced. > > However, after switching between SSB and DATA a few times to > compare the results, and also changing bands, I found that > the output in DATA is not consistent. Currently I am getting > about 65W for 50 selected. At one point on 20m I actually got > 50W. On 30m I am actually getting 20W (yes, 20W) with 50W > selected, absolutely no change to the audio input compared to > the other bands, and 4 bars of ALC showing. > > Back to the drawing board? > > ----- > Julian, G4ILO. K2 #392 K3 #222. > http://www.g4ilo.com/ G4ILO's Shack > http://www.g4ilo.com/blog.html G4ILO's > Blog http://www.g4ilo.com/kcomm.html KComm for Elecraft K2 and K3 > -- > View this message in context: > http://n2.nabble.com/K3-Beta-firmware-rev.-2.80%3A-Improvement s-to-AFSK-A%2C-DATA-A%2C-SSB%2C-AM%2C-FM%2C-DVR-tp2305650p2326853.html Sent from the Elecraft mailing list archive at Nabble.com. ______________________________________________________________ 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
