On Sun, Jul 4, 2010 at 7:01 PM, Ed Wilson <ed.wil...@ymail.com> wrote:
> > > Colleagues, > > I have had a Flex-3000 since January and recently purchased a Flex-5000. I > have always wondered, but never asked anyone, why the multimeter reading > seems to be about 20 dB higher than what the Panadapter shows. > > I assume that the multimeter shows true RMS power in the passband as > described in the manual. > That is correct. What the pan display shows is an FFT of the whole spectrum. Basically it is broken down into lots of little slices called 'bins'. If there are 2048 bins covering 20480 Hz of spectrum, each bin is therefore 10Hz wide. If you reduce the passband to the width of a single bin then the level of the pan display and the multimeter at that frequency will show the same thing. To get a feeling for how that works, keep cutting the BW in half. Each time the power display will decrease by 3dB. When you get down to the width of one FFT bin the power display will be equal to the pan level display. > > I also assume that when the AVG button is selected, the Panadapter shows > average power over a slice of spectrum, depending upon the sampling rate. I > also know that average power is not necessarily the same as true RMS power. > It just averages the FFT bin values over time. If you have a signal that is not changing in amplitude nothing will be different. If you have a signal that is changing in amplitude the value in the pan display will be averaged over time. -- Brian Lloyd, WB6RQN/J79BPL 3191 Western Dr. Cameron Park, CA 95682 br...@lloyd.com +1.767.617.1365 +1.931.492.6776 (+1.931.4.WB6RQN) _______________________________________________ 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://kc.flex-radio.com/ Homepage: http://www.flex-radio.com/
