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, ewkeh...@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,
jlt...@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-boun...@febo.com [mailto:time-nuts-boun...@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"<jlt...@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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