[time-nuts] Trimble replacement part-2

[Bob Camp]

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

On Oct 13, 2013, at 2:22 PM, quartz55 <quartz55 at hughes.net> wrote:

> I bought a Nortel/TB last month to go along with my LPRO-101.  I guess I'm satisfied with it for the $130 delivered with antenna for a 10MHz standard. Both are much better than anything else I have around the shop.  The only thing is, I'm still not sure where my frequency is.  I don't know how close I am to right on or how stable it is either.  According to the NTBW50AA book, the frequency accuracy is <0.8 x 10-10 (1 day average; Locked and Holdover modes).  But how can I tell?  LH seems to work with it to some degree, but I'm not sure what it is really telling me other than the software is working with it to some degree.
> 
> As far as a replacement for a TB or even just a basic 10 MHz standard, I'm thinking now I would have been better off spending the loot at Jackson Labs and owning something modern that is supported and has supported software with it and real accuracy specified.  I may end up doing that at some point anyhow.  I was almost willing to spend $300 or so for one of the eastern TB guaranteed to work, but am glad now I didn't.  I'd be willing to go as far as $5-600 at JL but I haven't approached them yet.
> 
> I looked into the VE2AZY project, but that too seemed to be fraught with issues and still questionable accuracy, plus I wasn't looking for another project, just a frequency standard I could depend on and specified frequency accuracy and stability.
> 
> My 2 cents.
> 
> Dave
> N3DT
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