[time-nuts] Another "atomic" clock question

Bob Camp lists at rtty.us
Sun Mar 2 15:07:08 EST 2014


HI

If that is what you currently have for references, then you probably need a “lab standard” to drive things. Having one reference for all the gear makes things *much* easier. You don’t have to mess with a lot of “which one’s right today” sort of decisions. 

That would make the GPSDO pretty much a slam dunk decision. You get both the reference and the calibration all in one box.

Bob

On Mar 2, 2014, at 2:56 PM, Bob Albert <bob91343 at yahoo.com> wrote:

> Nigel,
> 
> Thank you for your comments.  I see the situation a bit more clearly now, and will do some searches on Trimble and GPSDO and so on.  Right now I am interested in seeing what my options are, and deciding which way to go.
> 
> Yes this can become an obsession but I keep reminding myself that it's a hobby and isn't stopping me from eating or sleeping or breathing.  I do have fun with it.  Recently I bored a couple of visitors showing how my counter and signal generator drifted during warmup but eventually settled within about 10 ppb of one another, within about a half hour.  (Both units have 24/7 ovens.)  The generator actually accounts for nearly all the drift.  The counter is a venerable HP 5245L with 500 MHz plugin.
> 
> Bob
> 
> 
> 
> 
> On Sunday, March 2, 2014 10:33 AM, Tom Miller <tmiller11147 at verizon.net> wrote:
> 
> 
> ----- Original Message ----- 
> From: "Hal Murray" <hmurray at megapathdsl.net>
> To: "Bob Albert" <bob91343 at yahoo.com>; "Discussion of precise time and 
> frequency measurement" <time-nuts at febo.com>
> Cc: <hmurray at megapathdsl.net>
> Sent: Sunday, March 02, 2014 2:45 AM
> Subject: Re: [time-nuts] Another "atomic" clock question
> 
> 
> 
> bob91343 at yahoo.com said:
>> Okay you want numbers. Well, I think 10 ppb or thereabouts should do it.
>> Somewhere there is a discontinuity in accuracy plotted against cost and I
>> don't want to cross that barrier just yet. If I can get 1 ppb without a 
>> big
>> increase in cost, I'll take that.
> 
> How good is your crystal?
> 
> Junk crystals are good thermometers.  Ballpark is 1 ppm/degree-C
> If you are running ntpd, turn on loopstats and measure the temperature...
>   http://www.megapathdsl.net/~hmurray/ntp/slope.gif
> 
> I've been watching a 3 MHz ovenized crystal.  It was something like 4 for 
> $25
> from ebay.  It's a 2 in sq can, over an inch high.  It's got a few ppb of
> noise over minutes/hours and a few more ppb of drift/wander over 
> days/months.
> It took several weeks to stabilize after power on.
> 
> -- 
> 
> Is that 3 MHz OCXO one from Ridge? If so, I opened one up and was surprised 
> to find it did not have any foam insulation.
> 
> Tom 
> 
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