[time-nuts] GPSDO vs Rb standard

Bob Stewart bob at evoria.net
Thu Sep 19 00:32:59 UTC 2013


Bob, I've been mulling over the question of a case, and I was thinking of getting a 2M brick amp and putting it inside, bolted upside down to the heat sink.  Good idea?  Anybody got a busted one?

Bob





>________________________________
> From: Bob Camp <lists at rtty.us>
>To: Discussion of precise time and frequency measurement <time-nuts at febo.com> 
>Sent: Wednesday, September 18, 2013 7:22 PM
>Subject: Re: [time-nuts] GPSDO vs Rb standard
> 
>
>Hi
>
>The Rb's have a couple of issues:
>
>1) Its been years since they were set on frequency and they do have a yearly drift rate
>2) They have a temperature coefficient of drift that may be fairly large (0.1 ppb over -30 to +70)
>3) They self heat quite a bit, so they do move temperature / need a heatsink
>
>The solution to the temperature issue is a servo controlled fan. The solution to the first drift / accuracy issue is to calibrate them against something else.
>
>Bob
>
>
>On Sep 18, 2013, at 7:13 PM, "John C. Westmoreland, P.E." <john at westmorelandengineering.com> wrote:
>
>> Azelio and Fellow Time Nuts,
>> 
>> Isn't the GPS 1PPS signal supposed to be 'precise' to within what error?  I
>> imagine this is in the specs of the specific receiver -
>> but I was wondering if some of you have actually measured what that is -
>> and could report the numbers that you have found.
>> 
>> Thanks!
>> John Westmoreland
>> 
>> 
>> 
>> On Wed, Sep 18, 2013 at 3:07 PM, Azelio Boriani <azelio.boriani at screen.it>wrote:
>> 
>>> Instead of using the Rb's PPS, use the GPS receiver's PPS. Maybe you
>>> will find out that the Rb is slow... you can also check the Rb's PPS
>>> against the GPS's PPS.
>>> 
>>> On Wed, Sep 18, 2013 at 11:47 PM, Bob Stewart <bob at evoria.net> wrote:
>>>> I hooked the Rb's 1PPS to the trigger input on my old Tek 455, 10MHz
>>>> GPSDO to Channel A, .05us trace, and turned the lights out so I could
>>>> see it.  The 10MHz is marching right to left about 1 cycle every 20
>>>> seconds.  So, can I say that the Rb considers my GPSDO to be too fast by
>>> about 5ppb?
>>>> 
>>>> 
>>>> Bob
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