Re: 440 Band Off Frequency


Steve W3AHL
 

The Reference Oscillator is subject to frequency drift due to several causes, which result in the need to recalibrate it using the OTHER menu #51 adjustment.  I would try that before sending it in for repair.  While the oscillator is specified to have +/- 0.5 ppm frequency stability, that is only the short term stability with reference to gradual termperature change.  The long term aging is specified at +/- 1 ppm/year.  The oscillator frequency is voltage controlled via a D/A converter on the CPU, which its datasheet does not fully specify long term drift characteristics but probably exceeds 1 ppm.  I have seen units needing adjustment that be in the range of about 2 KHz shift on 440 MHz, but seemed to remain within spec afterwards.

I tend to recalibrate my 7K's Ref Osc about once a year.  Allow the unit to warm up with power on in the typical ambient operating environment for at least 30 minutes.  Then zero beat to the highest WWV frequency you can receive or calibrate as others mentioned to another reference signal (but not in FM mode, since the frequency accuracy will not be adequate for other modes).   Recheck the calibration occasionally to verify it is reasonably accurate still.  If not, there may be a problem with X1 on the DDS board or some other part.  I've never personnally known any of the loca hams to have to repair a 7K due to frequency drift that couldn't be adjusted with the menu 51 calibration (there's a reason it's there!), but VCO's can certainly fail, as can the DDS IC's and their controlling register chips.

Steve, W3AHL

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