At 10:36 AM 2/6/2007, Jeff Anderson wrote: >I know that my LP-100 Power Meter is calibrated band >by band, and so I'm wondering...how flat across the >spectrum (from 2 to 30 MHz) is response of the >directional coupler within the SDR's PA? > >Per the algorithm listed in Eric's email, any changes >in frequency response of the directional coupler could >cause the power reading to be inaccurate at those >frequencies.
Before leaping into calibration, and hacks to get around the current calibration model, one might want to contemplate what your real calibration model is. There's a "detector calibration" (the directional coupler/detector that Jeff refers to) which is certainly band dependent. Then, there's a "amplifier gain" calibration curve that says what the PA gain is for a given frequency. Finally, there's a Audio Interface level calibration, which is presumably constant by band, but varies between I and Q channels. There's also some I/Q calibration issues which are RF frequency dependent and some which are audio frequency dependent. Just as a note.. I'd implement these sorts of things with floating point numbers, and only do the dB conversions in the UI (which would include configuration databases). At some point, you have to move from floating point to actual hardware which tends to be fixed point, but that transformation should be separated out, as well. James Lux, P.E. Spacecraft Radio Frequency Subsystems Group Flight Communications Systems Section Jet Propulsion Laboratory, Mail Stop 161-213 4800 Oak Grove Drive Pasadena CA 91109 tel: (818)354-2075 fax: (818)393-6875 _______________________________________________ FlexRadio mailing list [email protected] http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archive Link: http://www.mail-archive.com/flexradio%40flex-radio.biz/ FlexRadio Homepage: http://www.flex-radio.com/ FlexRadio Knowledge Base: http://kb.flex-radio.com/
