George, The VFO / DDS error can be computed, based on the PSDR settings and radio's clocking design. I do not know anything about the F5K or F3K designs. I developed my correction spreadsheet with the help of Analog Devices' datasheet and simulation tool for their AD9951 DDS chip.
>From what I have read, the Spur Reduction does (sometimes) change the frequency tuning word sent to the DDS; so I keep it off during FMT's. 6 months ago I too was a newbie; finished 6th from last in my first FMT. I'm a retired measurement engineer, and now realize that "measurement" wasn't just a job I enjoyed very much, it was a passion! John Stuart, KM6QX _____ From: geo...@gloria.us [mailto:geo...@gloria.us] Sent: Monday, April 18, 2011 8:02 AM To: John Stuart Cc: FlexRadio@flex-radio.biz Subject: Frequency Errors in the F5K and F3K I have both an F5K and an F3K. Where do I get information regarding the errors that you mentioned. Must these errors be measured or can they be computed? I did use the Rubidium standard as my external reference into the F5K. I did not turn off spur reduction, however. How does spur reduction interact with the measurements? Please excuse my lack of knowledge regarding making measurements. Am a newbie for FMT. I am not even sure how to ask the right questions. Thanks George K2CM (who did miserably on 40M in the last FMT.....80 meters was <1hz.) -------- Original Message -------- Subject: Re: [Flexradio] [Bulk] FMT Results From: "John Stuart" <j.w.stu...@comcast.net <http://j.w.stu...@comcast.net%3e> >; Date: Sun, April 17, 2011 7:16 pm To: <FlexRadio@flex-radio.biz> (OK Brian Lloyd, I'm jumping in with both feet) With my Flex-1500, and a 'perfect' 10 MHz external reference oscillator, and PSDR set for CWU mode, a 600 Hz "Pitch Freq.", Spur Reduction turned off, Clock Offset set to 0, IF set to 0 Hz, and the VFO set to 10.000 000 Hz; the Flex's QSD (Quadrature Sampling Detector) will be receiving at 9,999,999.958 Hz, i.e. 42 mHz low. (Actually it's 41.822 mHz low, if your still paying attention) That's a one sentence summary of what I have learned about my Flex-150 over the past few months. With some test equipment, needle pointed probes, and a magnifying glasses, I have figured out the Flex-1500's clocking scheme and discovered some DDS control 'anomalies' (software error?). I then developed an Excel spreadsheet that calculates the exact DDS output frequency, which I have confirmed with 1) direct DDS chip output measurements, 2) mHz resolution signal generator reception tests, and 3) GPS locked radio station reception tests. I doubt that my Excel worksheet would apply directly to the Flex 5k or 3k, but it should in principle. The DDS chips are not 'exact', and if you need to know your VFO frequency to better than 1 Hz, then you need to know how much the DTW (Digital Tuning Word) is truncated. For the Flex-1500, the error can be between -0.004 to -0.042 Hz. Then there is the analog to digital sample rate correction that may also need to be made. For the Flex-1500 this is controlled by another crystal oscillator, which is not referenced to the external 10 MHz oscillator. I plan to write all of this up into some Wiki technical notes (with everyone's help, of course). Finally, to answer Jim's question below; Given all of the settings in my first paragraph above, when I 'receive' my 10 MHz Rb oscillator signal, I measure a 600.042 Hz audio tone at the Phones jack. John Stuart, KM6QX Lafayette, CA -----Original Message----- From: flexradio-boun...@flex-radio.biz [mailto:flexradio-boun...@flex-radio.biz] On Behalf Of Tim Ellison Sent: Sunday, April 17, 2011 4:07 PM To: jim; 'Jeff Singer'; FlexRadio@flex-radio.biz Subject: Re: [Flexradio] [Bulk] FMT Results Close, but it may not be exactly a 0 DDS offset. My 5000 needs -2 and my 1500 needs +3 to be dead on frequency with a Rb clock. -Tim -----Original Message----- From: flexradio-boun...@flex-radio.biz [mailto:flexradio-boun...@flex-radio.biz] On Behalf Of jim Sent: Sunday, April 17, 2011 12:55 PM To: 'Jeff Singer'; FlexRadio@flex-radio.biz Subject: Re: [Flexradio] [Bulk] FMT Results A related, dumb, question... If one takes a 10Mhz standard and uses it for the "signal" as well as the local reference, should the DDS offset be "0" ? Jim W4YXU _______________________________________________ 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.flexradio.com/ Homepage: http://www.flexradio.com/ _______________________________________________ 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.flexradio.com/ Homepage: http://www.flexradio.com/
