freq calibration

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  • Updated 1 year ago
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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.
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Posted 1 year ago

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Photo of Greg - N8GD

Greg - N8GD

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Official Response

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 1⁄2 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.