It is nice to see that screen updating really fast. It looks cool and helps to see transient events. If you have the CPU resources, go for it. But it turns out that, for any given set of DSP buffer parameters and sample rate, there is a maximum frame rate.
The Panadaptor display is created by doing a Fast Fourier Transform (FFT) on the sampled data. Each FFT is performed on the data collected in the most recent DSP sample buffer. We can determine the time this represents by dividing the buffer size in sample by the sample rate. That will give you the amount of time represented by each FFT. If you do the reverse, i.e. sample rate divided by DSP buffer size, you get the number of FFTs per second (frame rate). Setting the display frame rate to a value greater than this does nothing but waste CPU time as you are just displaying the same information over again. Here are the maximum frame rates (FFTs per second) for various standard settings: Sample Rate Buffer Size FFT rate 48000 2048 23.4/s 96000 4096 23.4/s 96000 2048 46.8/s 192000 4096 46.8/s 48000 4096 11.7/s I threw in the last one because that is what I am using with WSPR on my Flex 5000. Since the WSPR signal is so slow, approximately 1.5 baud, the narrow bin-width gives me the ability to see weak WSPR signals on the waterfall of PSDR. I would use even longer integration times if possible but this is the best that PSDR gives me. Still, the original point was to suggest that you look at your sample rate and DSP buffer size and then set the frame rate accordingly. There is no advantage to setting the frame rate any higher than the rate at which PowerSDR does the FFTs that drive the display. BTW, if you are looking for signals that come and go very quickly, e.g. CW and some other digital modes, you actually need to increase sample rate and/or reduce buffer size. Remember that the FFT is averaging the power in each bin giving you a picture of the total energy in each bin for the duration of the FFT. If your FFT goes on too long, a transient event will just get lost in the noise energy. Hopefully this gives you some things to think about when adjusting the settings of PowerSDR when trying to optimize for various modes. *THIS* is what SDR is really all about and why SDR really is the wave of the future. -- Brian Lloyd, WB6RQN/J79BPL 3191 Western Dr. Cameron Park, CA 95682 [email protected] +1.767.617.1365 (Dominica) +1.931.492.6776 (USA) (+1.931.4.WB6RQN) _______________________________________________ FlexRadio Systems Mailing List [email protected] 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.flexradio.com/ Homepage: http://www.flexradio.com/
