From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Brian Lloyd Sent: Friday, September 05, 2008 8:57 AM To: Dudley Hurry Cc: Don Sachnoff; flexradio@flex-radio.biz Subject: Re: [Flexradio] Issue with V1.14.0
On Sep 4, 2008, at 9:08 PM, Dudley Hurry wrote: > Don, > > Using VAC, you use the VAC TX Gain to regulate your output, if you > are using the conventional method of physical cables to and from the > computer sound card, use the TX gain. (mic gain) as you would with > any regular radio. > > In VAC I used the default values. I can send you my values if you > would like. Normally I would peruse the schematics to try to understand how things work in a radio. Not being able to do that with the F5K, it would be nice to understand how signal levels are managed in the transmit chain. --- You can peruse (and that is the correct word.. Lots of detailed examination required) the equivalent of the schematics: the source code for PowerSDR and dttsp. There is no "power control" per-se inside the physical radio. The output of the QSE (vector mod) gets amplified in an essentially fixed gain chain, so the thing that determines output power level is the audio level fed to the modulator, which in turn is probably entirely determined by the digital data stream. (I don't recall seeing any code to change the DAC gain, but, OTOH, I haven't looked for it) In more traditional SSB radios one has no choice but to control transmit power level by varying the mic (low-level) gain. Gain settings for the rest of the stages are fixed. With the Elecraft K2 we have, I found it works better to optimize the baseband signal level (audio) and then use the power output control to vary the transmitter power. So, how does the F5K work? I would naturally lean toward fixing the baseband signal level and then use the transmitter power level control to set the TX power output but now you are saying that we should manage power using the mic gain. ----- Frank or Bob would be the ideal folks to answer the details, but, I suspect it doesn't make much difference. All the DSP is floating point, so it's not like you have the traditional analog problem of "saturating an amplifier". There are almost certainly some interesting interactions with things like compressors and limiters, though. In general, you want enough (analog) gain on the mic input to get the signal well up into the dynamic range of the audio A/D that's digitizing it, but after that, it's all floating point. _______________________________________________ FlexRadio Systems Mailing List FlexRadio@flex-radio.biz http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archives: http://www.mail-archive.com/flexradio%40flex-radio.biz/ Knowledge Base: http://kb.flex-radio.com/ Homepage: http://www.flex-radio.com/
