Joe W4TV wrote: > Closed loop power controls are not appropriate to SSB systems because time > constants sufficient to maintain constant power across the > IF passband for digital operation would result in frequency > dependent clipping and/or compression in voice operation.
Most digimode programs include a tune button which outputs a tone at the selected output; psk's idle is a simple two-tone. One option (and I expressed this a year or so ago to the Elecraft folks) would be to offer an IMD calibration at the IF level for a known two-tone response, to determine whether at least that stage is being overdriven. The DSP should have a fairly good idea at that point. If the two-tone signal used is a PSK idle tone at the selected AF on the waterfall display, a rig control command to read the IMD calculated would be just peachy. Digimode programs could then have a dedicated button to send an idle tone, read the IMD, and adjust the power. Regular communications could then commence. A further advantage of this approach is that the actual power out could be measured during this calibration period from either the built-in wattmeter or the rig control command, and reported in real time, and thus the knob could (or again, rig control) could be used to achieve the output power desired by the user. Elecraft's response was that perhaps the IMD calculation could be done on the computer side; I'm not clear whether the new monitor out function makes that possible or not, but if it does, that would be an approach that could be made to work today, modulo the limitation that the IMD calculated from the sound card will be a little worse due to the additional ADC of the sound card, whereas a digital report from the K3 IF would be accurate. (And not to mention that an overdriven line input would result in a drastically wrong IMD, but that's likely to have been already taken care of by the digimode RX setup.) In summary, I believe it's possible to provide closed loop control for both power and drive/IMD readings for modes such as PSK, but not during a QSO where the signal characteristics vary; instead provide enough CAT commands and signal quality measurements from the K3 RF OUT and IF OUT stages so that and digmode authors are willing to provide a "TX CAL" tune button. (Doing in the k3 utility wouldn't be helpful because the precise audio settings used by the digimode program for TX are important.) I'm willing to step up and try this for fldigi. Leigh/WA5ZNU _______________________________________________ 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
