Calibrate Local Oscillator in my 6400M

Andy W3LI

Staying at home like everyone else I decided to Cal the local oscillator as per the user manual pg 130. It does not say but I will assume that this is done in the AM mode as WWV transmit AM.
I set the Cal frequency at 15 mhz as it gave me a signal of S8&9. The Offset came back as -953.
Is that -953 hz in parts per billion? Manual does not say.

HCampbell WB4IVF

Andy W3LI

OK, Thanks for the confirmation as the manual does not mention such.

Robert Lonn

Al K0VM

Andy W3LI

Sure U do.....April Fools

KC2QMA_John

Andy W3LI

Hi John, long time no hear.

Al K0VM

KD0RC

Mine was a little over 1200. I have since connected a GPSDO and it came in at zero when calibrating with WWV at 20 MHz. I have recalibrated a couple of times to see if this is a fluke, and it has stayed at zero. 73, Len, KD0RC

Dwayne_AB6A

I use an external GPSDO. 

KC2QMA_John

OK so around 950 to 1500 is normal for the stock internal local OSC?

Dwayne_AB6A

-1347 with the internal TCXO and -7 with the external GPSDO on 10Mhz.

KC2QMA_John

I think as i get more into digital modes I will look into a GPSDO.

Al K0VM

As long as it stays in the range that the software cal is able to correct, it should be fine..  Not sure what that range  is though.
AL, K0VM

Brian Denley KB1VBF

Mine is zero (No lie!) with an external GPS.

KC2QMA_John

WOW Brian, what GPSDO are you using?

Brian Denley KB1VBF

BG7TBL one on EBay.  About $150.  I did have to buy the cable to attach to the Flex 10 MHz input conn.  After the setup and the GPSDO and my Flex said they were both locked, I basically pushed the cal button and it came back at 0 at 10 MHz.  Kinda surprised me.

Dwayne_AB6A

Mine is 4 on 10Mhz this minute but the Flex will return 0 if it does not find a signal to sync to.

Brian Denley KB1VBF

Since the Flex said it was locked on external, can I assume it found the signal?

Dwayne_AB6A

No - Note how the radio will switch frequency to calibrate. 10MHz should be good!

Brian Denley KB1VBF

No? You don’t think locked means it sees the 10 MHz external GPSDO?

Dwayne_AB6A

No means Yes it is locked on GPSDO, but calibration requires you enter 10 (Mhz) and click Start next to the Call Frequency. The radio will then test calibration against a 10 Mhz reference signal. It will then adjust offset in ppb. Click start and let us know what it says. Mine this minute is bouncing between -3 and +4. Essentially noise, but not 0. A cold GPSDO will have a much higher value but better than the internal TXDO. It would be surprising it always comes back 0 but as a warning, if it does not find a signal (wrong antenna etc) it will come back 0.

Brian Denley KB1VBF

Dwayne:
OK yes that's what I did (press start) and it came back with zero.  I'm sure if I do it again i'll get 10 or 7 or -15.  But I did like seeing that zero!  hehe

Brian Denley KB1VBF

Dwayne_AB6A

That’s awesome!

Geoff AB6BT

This is all very interesting. I have a question. What are the practical differences when using a DSPDO? If the radio is capable of of generating an offset to a known frequency standard, WWV for  example, What is the advantage of using a GPSDO?

Brian Denley KB1VBF

Not that much Geoff.  I'm not sure you really care whether your contact is 5 Hz off or .00005 Hz off.  I like mine for the frequency calibration and also the time keeping which is exact.

Dwayne_AB6A

There is a frequency test contest conducted several times a year. I hope to compete this year.

Dwayne_AB6A

GPSDO has a high degree of stability and accuracy over and above the standard TXDO. IMO, really only matters at UHF and beyond.

George KF2T