[Elecraft] Adjusting reference frequency some time after tx compensation

[David Anderson]

David

I did almost the same, I did the extended temperature calibration with the XG50 and then afterwards did the REFCAL calibration on the 5th harmonic of my Z3801 10MHz GPSDO.

This was last year and today I rechecked on the same 50MHz signal and found it was within a Hz of where it was before.

Then I thought I will check it on 10MHz and it was about 40 Hz off. 

So setting up REFCAL at the highest frequency does not seem the best way as I had previously imagined it would be.

I have now calibrated at 20 MHz which is giving almost the same point at 10 MHz and wee bit difference at 30 MHz. Now of course 50 MHz is 40 Hz out, but I am not that fussed as I don't see me using the KX3 for anything at that frequency as I have another 50MHz rig with more power.

As a sanity check I tried another GPSDO and a 10 MHz OCXO and they all agreed.

As to your second question, I believe that you do not need to repeat the extended temperature frequency cal if you recalibrate the REFCAL. 

Summary, I find the same discrepancy between calibrating at 50MHz and 20 or 10 MHz. I also find that the KX3 does keep its frequency calibration setting very well over a long period of time.

73

David Anderson GM4JJJ 

> On 15 Feb 2015, at 21:51, David Orman <ormandj at corenode.com> wrote:
> 
> Hi,
> 
> A while ago (months) I did the extended temperature compensation procedure
> using the XG50, which seemed successful. I decided to tune up to 20MHz
> recently, and noticed when in CW mode, if I ran spot (manual) I was off, by
> a small margin (33Hz). I'm assuming this is normal as time goes on, is this
> a correct assumption?
> 
> Second question: assuming it is normal, and I should periodically
> re-calibrate using the XG50 or a known signal like WWV, is it safe to go to
> ref cal in the menu, unlock it, and manually tune/zero beat to adjust the
> frequency - without losing the calibration gained from doing the extended
> temperature compensation procedure? I'd rather not have to repeat that
> process any more than necessary, so I'm hoping the look-up table that
> generates is for something like offset based on temperature and so remains
> constant, and only the main reference calibration needs changing? I did
> this to test, and the menu item is still 'REF*CAL'. Tapping CMP while in
> this menu option, I have verified it is set to 'CUSTOM'.
> 
> I appreciate any feedback,
> David
> _______________________________________