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freq calibration

Wayne Member ✭✭
Using 2.1.33 version noticed 15 mhz in freq box read manual and changed it to 10mhz then set vfo to 10 mhz had 9 on s meter strong signal hit start and I guess it worked right after about 20 seconds or so it completed and -640 ppb showed up in the offset box. Didnt really notice any difference still have green check next to txco amd locked. So what does the -640ppb mean and how far off was my frequencies since I never done this when I upgraded to this version but I never had anyone question my frequency either ... anyway good job flex I guess it worked.


  • Greg N8GD
    Greg N8GD Member ✭✭
    edited June 2018

    Flex transceivers have always had this feature.  Earlier versions of Smart SDR did not implement it very well, but it is very good nowadays.  Those models that support the GPSDO and have it installed don’t need this calibration feature since that add-on unit takes care of locking the TCXO (Temperature Compensated Crystal Oscillator) to a GPS satellite’s frequency standard (which is highly accurate).

    Here’s the math:  One part per billion (ppb) is .000000001.  You tuned the radio to 10 MHz, so 1 ppb at that frequency is 10 MHz X .000000001 = .01 Hz (one hundredth of a Hertz).  So, since you read -640 ppb after calibration, it means that with one ppb being .01 Hz, we thus have -640 X .01 Hz = -6.64 Hz.  Your radio had its frequency adjusted downward 6.64 Hz at 10 MHz.  At that frequency, without the correction, your dial frequency would have read 10.000000 MHz but would have actually been tuned to 10.0000064 MHz or 10,000,006.40 Hz, transmitting about 6 Hz too high (not much!).

    Bob Brown, N8OB, ran a 6300 in the ARRL FMT (Frequency Measurement Test) three years ago, and even without the GPSDO in that model, he consistently had an error of less than ½ Hertz in the lower frequency bands and around 6/10 Hz at 20M.  Pretty good!  Here’s the link to his post:


    You can find further info on this subject by searching for FMT on the Community.

    Flex makes some nice and highly accurate radios.
  • Wayne
    Wayne Member ✭✭
    edited June 2018
    Wow ... less than 7hz hardly worth adjusting for!

    Thanks for the explanation!
  • Greg N8GD
    Greg N8GD Member ✭✭
    edited April 2018
    i don't know what the specs are, but some of the digital modes are picky about frequency accuracy.  i don't think a few Hertz are a problem, but tens of Hertz could be.  A lot of legacy radios have TCXOs available as an option, and they are recommended for the digital modes.

    The GPSDO available on the higher end Signature Series radios provides accuracy to 10 to the minus 12, or one part per trillion!
  • w5ap
    w5ap Member ✭✭

    I found that at 15 Mhz the calibration didn't work

    But when I put in 10 Mhz it did work

    So I guess I wasn't picking up a freq standard station at 15 Mhz.


  • Tim - W4TME
    Tim - W4TME Administrator, FlexRadio Employee admin

    @w5ap If the frequency cal isn't working on 15 MHz, then the issue is either low signal strength or too much variability in the signals strength (selective fading). Using either 10 or 15 MHz or any other known signal source should be sufficient for calibrating the radio.

  • KD0RC
    KD0RC Broomfield, COMember, Super Elmer Moderator

    I live 50 miles south of WWV, so I always have great signal strength to work with, day or night. WWV transmits on 2.5, 5, 10. 15 and 20 MHz. We all tend forget about 2.5 and 5 MHz, but they are often MUCH stronger, especially in the evening depending on how far you are from Colorado. My suggestion is to try them all to see which is strongest, then use that one to do the calibration. You do not have to have the rig tuned to WWV to do the calibration, it jumps there temporarily then comes back to where you were tuned (you do need to have an antenna on the ANT1 jack - the cal does not work on any other antenna input).


    Len, KD0RC

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