Hi Brian, Great info - thanks!
That is so amazing to think that the radio can know when it has a problem like that and adapt to it - wow. Man, these guys at Flex are awesomely smart! Best regards, Michael Jones SCSI Toolbox LLC www.scsitoolbox.com 303-972-2072 -----Original Message----- From: br...@lloyd.com [mailto:br...@lloyd.com] On Behalf Of Brian Lloyd Sent: Wednesday, January 13, 2010 12:43 PM To: mi...@scsitoolbox.com Cc: flexradio@flex-radio.biz Subject: Re: [Flexradio] "SR" button On Wed, Jan 13, 2010 at 10:13 AM, Michael Jones <mi...@scsitoolbox.com> wrote: > I know the "SR" button stands for Spur Reduction, but I'm not certain > what that means in practical terms. > > Is a spur like an image signal? Not really. The local oscillator (VFO) is a DDS oscillator that is programmed to generate a certain frequency. Normally the Flex uses an IF frequency of 9kHz. So if you want to receive a signal at 14,009 kHz normally the VFO would generate 14,000 kHz. 14,000 kHz when mixed with 14,009 kHz produces the IF at 9kHz. But sometimes a programmed value in the DDS VFO produces an internal divisor that results in not only the desired output but one or more additional low-level spurious outputs (spurs). Flex has identified which values do this and change the behavior of the radio slightly. If the DDS VFO were to produce spurs at a VFO frequency of 14,000kHz but not at 13,999 kHz then PowerSDR commands the radio to use 13,999kHz for the VFO frequency but then changes the IF to 10kHz. Now 14,009kHz - 13,999 kHz = 10kHz. So, in short, PowerSDR changes both the VFO frequency and the IF frequency behind the scenes so that the spurs do not show up. Pretty clever those Flexians. > What got me thinking about this is the fact that CW Skimmer wants this > to be turned off. I can see that Skimmer sees things differently with > it on or off, but I don't know why that is. It is because of the magic hand-waving above. CW Skimmer always uses the same IF so the DDS VFO *must* produce the expected frequency or the frequency calculated in CW Skimmer would be incorrect. > Also - is this something that has to do with receive only? No, this is done for transmit as well. > What's really on my mind is - when I stop using Skimmer is it very > important that I turn SR back on? Yes. It not only avoids spurs but it makes tuning much faster because PowerSDR doesn't need to change the frequency of the VFO for every 1Hz of frequency change. -- 73 de Brian, WB6RQN/J79BPL _______________________________________________ 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/ Message delivered to arch...@mail-archive.com
