[time-nuts] GPSDO for a week

[Markus Kern]

On 28.02.2009, 00:47 Tom Van Baak <tvb at LeapSecond.com> wrote:

>> Thanks a lot for taking the time to do these measurements Tom.
>> 
>> If I am interpreting the data correctly the ADEV stays below
>> 3E-(8+tau) out to tau=1000s and is above that for tau=10000s. So the
>> Thunderbold is indeed not suitable for VLBI at 40-50MHz with
>> integration times longer than 1000s.

> I'm not sure what you mean by the expression: 3E-(8+tau). For
> example, if you plug in tau = 1000s into that equation, you get
> 3e-1008, which isn't right.

Your are right, of course. I just realized I made the same mistake in
my previous post. The ADEV requirement is 3E-9 * tau at tau or
equivalently 3E-(9+x) at tau = 1Ex.

> Also how does this compare with your earlier requirement of
> 3 ns at 1 second (which would be 3e-9). I'll help, but I'm a bit
> confused what your performance goal is and how that relates
> to 50 MHz.

At f = 50MHz the period is T = 1/f = 20ns and a 50 degree phase error
corresponds to T*50/360 = 2.7ns = 2.7E-9s (or 3ns at 46 Mhz). Since
the phase error must be below 50 degrees over the entire signal
integration time the required ADEV decreases with the integration
time d as 2.7E-9 * tau at tau = d.


> /tvb