[time-nuts] Chinese GPSDO 10 MHz error

Tim Shoppa tshoppa at gmail.com
Thu Aug 27 10:06:17 EDT 2015


Many hobbyist GPSDO's work, by counting OCXO cycles between some number of
GPS PPS assertions.

Software adjusts EFC based on frequency count. Often times the frequency
count used as input to the software has not just random +/- 1 bobble in
last digit, but also an extra count or two in last digit depending on the
hobbyists' gating choices. The systematic extra count or two will result in
a frequency offset between hobbyist GPSDO and PPS. Other times bugs in the
software that drives EFC might result in a systematic frequency offset.

We just had a poster last week who came here with such a scheme.

Tim N3QE

On Wed, Aug 26, 2015 at 11:54 PM, Bob Benward <rbenward at verizon.net> wrote:

> So how does a frequency lock work?  How is it implemented? Can someone
> sketch a schematic?
>
> And what equipment or technique is used to measure a 2hz error at 100GHz?
>
> Bob
>
> >>> -----Original Message-----
> >>> From: time-nuts [mailto:time-nuts-bounces at febo.com] On Behalf Of Tim
> >>> Shoppa
> >>> Sent: Wednesday, August 26, 2015 5:18 PM
> >>> To: Discussion of precise time and frequency measurement
> >>> Subject: Re: [time-nuts] Chinese GPSDO 10 MHz error
> >>>
> >>> Full KE5FX evaluation of BG7TBL GPSDO here:
> >>> http://www.ke5fx.com/gpscomp.htm
> >>>
> >>> I'm wondering out loud if it might, like many hobbyist GPSDO's, be
> >>> frequency-locked rather than phase-locked and thus susceptible to
> last-digit-
> >>> counter bobble in some long-averaging counter.
> >>>
> >>> Tim N3QE
> >>>
> >>> On Wed, Aug 26, 2015 at 3:18 PM, Perry Sandeen via time-nuts < time-
> >>> nuts at febo.com> wrote:
> >>>
> >>> > Hi,
> >>> >
> >>> >
> >>> >
> >>> > On the EEVBLOG  (http://www.eevblog.com/forum/index.php)
> >>> >
> >>> >
> >>> >
> >>> > They mention that the "2014-11-06"version GPSDO that was “most
> >>> > extensively tested, so far (by ke5x and others).
> >>> >
> >>> >
> >>> >
> >>> > (Has a) known bug, outputfrequency is not exactly 10mhz
> >>> > (9,999,999.999,800 Hz). This translates to ~2hzerror at 100ghz.”
> >>> >
> >>> >
> >>> >
> >>> > A question is if this bug isjust for this particular model or all
> >>> > other versions suspect?
> >>> >
> >>> >
> >>> >
> >>> > I realize that in and of itsself it is very small error, but errors
> >>> > tend to multiply or cause incorrectconclusions to testing.
> >>> >
> >>> >
> >>> >
> >>> > Another question is will the LHdisplay unit they offer work with
> other
> >>> > Trimble units such as are offered byRDR?
> >>> >
> >>> >
> >>> >
> >>> > That said, these models seem tobe a very nice turn-key systems.
> >>> >
> >>> >
> >>> >
> >>> > Regards,
> >>> >
> >>> >
> >>> >
> >>> > Perrier
> >>> >
> >>> > _______________________________________________
> >>> > time-nuts mailing list -- time-nuts at febo.com To unsubscribe, go to
> >>> > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> >>> > and follow the instructions there.
> >>> >
> >>> _______________________________________________
> >>> time-nuts mailing list -- time-nuts at febo.com To unsubscribe, go to
> >>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> >>> and follow the instructions there.
>
> _______________________________________________
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to
> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
>


More information about the time-nuts mailing list