Julian, G4ILO said: > I don't think it is anything to do with this revision. I first noticed this > a few months ago, after one of the updates that made some changes to the > ALC. Adjusting TXG VCE may be the answer, but the other change I made was to > avoid tuning at 5.0 or 50W. The K3 recalibrates the power when you press > TUNE at those exact power levels, and if it is looking into a mismatched (or > varying, as you adjust the ATU) load then it mucks up the calibration.
Except when performing a power calibration, I never set my requested power to 5.0W or 50W for the reason Julian describes. Actually, this is not a power calibration issue at all, but it is a difference in the radio's performance as a result of the firmware revision. Even after performing the power calibration at 50W into a dummy load to eliminate calibration as a concern, I find that version 2.73/1.98 delivers significantly higher power than 2.67/1.96 at the same PWR control setting. As AD7OG did, I observe that with a PWR control setting of 48 watts and TXG VCE at 0.0 dB I get a reading of 90 watts (9 bars) delivered power at an audio frequency of 1000 Hz in DATA A mode. The IMD in PSK31 is correspondingly bad (at 90W delivered power, the measured IMD is around -18 dB instead of the desired -24 dB or better). The delivered power is not quite this high at higher audio frequencies, but still well above the requested 48 watts. AFSK A mode behaves similarly to DATA A, but unlike PSK31 the consequences in RTTY are relatively minor (no IMD issues to worry about - if I were using low tones, I would hold the delivered power to 100 watts or less simply to avoid the possibility of transmitting audio harmonics, but with high tones this is not likely to be a problem). In order to hold the delivered power down to no more than 50 watts so as to give acceptable IMD values for PSK31, I must either adjust the PWR control down to a setting much lower than the power I actually want, or set TXG VCE to a value of -2.0 dB or so as suggested by NW8L. The precise power delivered varies somewhat with audio frequency, but settings of 48W for the PWR control and -2.0 dB for TXG VCE seem to deliver reasonable PSK31 performance here. I expect that these settings may continue to change with future firmware revisions. 73, Rich VE3KI K3 #1595 _______________________________________________ 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
