[time-nuts] FE-5680A Mechanical Question
John Ackermann N8UR
jra at febo.com
Thu Jan 12 16:01:44 UTC 2012
I think you have to define "better," though. A GPSDRbO will have better
holdover performance (e.g., stability when the GPS signal goes away)
than one using an OCXO, but the OCXO is quite likely to have better
short term stability than the Rb.
If holdover isn't an issue, you need to find the "Allan Intercept Point"
(term stolen from David Mills and NTP) to see where the GPS and
oscillator ADEV curves cross over. That will tell you how long a loop
time constant you want, and will let you look at the combined ADEV for
each type of oscillator. You may find that a decent OCXO gives better
performance overall than an Rb.
John
----
On 1/12/2012 10:37 AM, EWKehren at aol.com wrote:
> with the good long term performance of Rb's and the presently available
> 5680A for $ 40 a Shera Type controller will make available to any one on the
> list a reference better than a Tbolt for less money than a Tbolt. Repeating
> my self I would also add a "clean up" OCXO in order to get the very best.
> Bert Kehren
>
>
> In a message dated 1/12/2012 8:34:54 A.M. Eastern Standard Time,
> jltran at att.net writes:
>
> David,
>
> I have been following discussions on the list about a GPSDRbO for a year or
> so. Some interesting challenges and probably best implemented in a
> 'stable'
> environment rather than portable operation but as best I can tell, it would
> require a very stable and good antenna location, stable and clean power,
> and
> I was thinking of using something like an LPRO-101 with an Ext C Field
> input, a Shera type controller, and a GPS timing receiver, though, I
> suspect
> there are likely to be some 'multi-tasking' receivers out there that will
> look at several sources including GPS, GLOSNASS, etc.
>
> While the project might be fun, for portable work, it is likely far easier
> and probably just as good (almost), to use a Tbolt.
>
> In any event, something to think about for the future.
>
> Joe
>
> -----Original Message-----
> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
> Behalf Of David
> Sent: Wednesday, January 11, 2012 11:12 PM
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] FE-5680A Mechanical Question
>
>
> How would a GPSDRbO work? Phase lock the DDS output to the GPS? Phase lock
> a VCXO to the GPS and then phase lock to the RbO on loss of GPS lock?
>
> On Wed, 11 Jan 2012 22:55:58 -0600, "J. L. Trantham"<jltran at att.net>
> wrote:
>
>> Bill, Brian, Bill, and Peter,
>>
>> Thanks for the info. All I need now is a 'project' to incorporate the
>> unit into.
>>
>> In the back of my mind, I have the thought of a 'box' that will be
>> battery powered or 110 VAC powered (perhaps with an internal SLA
>> battery) and include a GPSDO and Rb unit (possibly a GPSDRbO) for the
>> purpose of a 'reference' for portable operation in the microwave
>> regions.
>
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