[time-nuts] Chinese GPSDO 10 MHz error

[Azelio Boriani]

The simplest form of a frequency locked loop is the XOR gate, when the
driving signals are 50% square waves. To achieve lock, the phase
difference will be proportional to the voltage needed to the VCO to
generate the desired frequency. Start with a 5V digital gate, suppose
your VCO needs 2.5V to be in frequency: the XOR output will be at 50%
duty cycle to generate, out of an RC, 2.5V and the phase difference
(between the reference and the VCO) will be 90 (or 270) degrees. The
difference will be more or less than 90 if the required voltage is
more or less than 2.5V (positive EFC) or will be more or less than 270
if the VCO has a negative EFC.

On Thu, Aug 27, 2015 at 5:54 AM, 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
>>>> >
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