[time-nuts] Trimble replacement part-2

[Bob Camp]

Hi

The manual is not correct when it implies that as the tuning resolution. There are many months of threads here digging into the how and why of the real tuning resolution.

A 1x10^-(anything) tuning resolution is a possible thing with an OCXO - just gang up enough DAC's. That's not where the limits lie in terms of a GPSDO. You can do a modified C field drive on an Rb to get the same sort of thing. You are still stuck with the real issues. 

Bob

On Oct 13, 2013, at 4:29 PM, Bob Stewart <bob at evoria.net> wrote:

> Now there's an interesting project:  turning Bert's board into a controller for an Rb standard. = )  If I'm reading the manual right it says: "For an FE-5680A device with an output frequency of 10 MHz, this corresponds to a relative frequency setting resolution of 1.7854E-14."  This should be the same for a timing FE-5680A modified to accept RS-232 and output RF, right?
> 
> Bob
> 
> 
> 
>> ________________________________
>> From: Bob Camp <lists at rtty.us>
>> To: Discussion of precise time and frequency measurement <time-nuts at febo.com> 
>> Sent: Sunday, October 13, 2013 3:06 PM
>> Subject: Re: [time-nuts] Trimble replacement part-2
>> 
>> 
>> Hi
>> 
>> All of the surplus GPSDO's are designed for cell tower applications. They are time references rather than frequency references. That's true of a TBolt, the HP 38xx's, the Nortel / Trimble's and the Symmetricom / Trimbles. It's also true of many the TIme Source series of parts (for various reasons). 
>> 
>> If you want a unit with tight *guaranteed* frequency accuracy for a wide range of averaging (say < +/- 10 ppt 10 seconds to forever), you want a GPS disciplined Rb not a GPS disciplined OCXO. They are out there. Plan on spending a couple thousand dollars. Even with those units, there is no software that will tell you what the frequency accuracy currently is. All it will tell you is "locked and running". To *know* that the frequency is correct you still need an external high accuracy reference to compare to. The gizmo's main spec is not going to be ADEV. ADEV won't tell you what the actual frequency is.  
>> 
>> Bob
>> 
>> 
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