[time-nuts] Disciplining a Rubidium with a Thunderbolt.

Bob Camp lists at rtty.us
Tue Jul 12 16:21:25 UTC 2011


Hi

Any time you get into something like this, there are a lot of qualifiers on
everything. That makes for a number of special cases. Ignoring them and
looking at the most likely: 

1) Your typical modular Rb will beat your typical good OCXO past a few
hundred seconds on short term stability.
2) The same Rb will start to degrade on short term stability past a few
thousand seconds. (Curve goes down, levels, and then starts to come back
up).
3) GPS it's self starts out pretty awful. It just keeps getting better the
longer you look at it. 
4) Most good GPS's will get better than most modular RB's between 5,000 and
50,000 seconds. 
5) We are talking about radio here. The atmosphere does matter. There are
some daily cycles that might push you out past 86,000 seconds for a unit
that's stable under all conditions. You could go with an L1/L2 receiver if
you have one available. 

Of course, what matters is "what do the ones I have do" and not what a
typical population does. You might select parts that do a bit better than
typical. That is likely to involve some measure and adjust cycles.

If you toss in a TBolt rather than a simple GPS receiver, it's going to
clean up some of the GPS crud for short time intervals. That may or may not
help things overall. It's not likely to hurt anything though. 

That's the overview, there are a whole lot of grubby little details each
step along the way. 

Bob




-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Tim Tuck
Sent: Monday, July 11, 2011 9:16 PM
To: Discussion of precise time and frequency measurement
Subject: [time-nuts] Disciplining a Rubidium with a Thunderbolt.

Hi all,

Just wondering how many people have used John Miles work @ 
http://www.ke5fx.com/tbolt.htm, or similar, to discipline a rubidium 
oscillator and if so...

1. what was the RB of choice ?
2.have any measurements of phase noise etc. been published on such a rig ?
3. Are there any published how-to's etc. available ?

I'd like to build such a beast as my lab standard so any help appreciated.

thanks

Tim

-- 

VK2XTT :: QF56if :: BMARC :: WIA :: AMSAT-VK :: AMSAT

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