[Elecraft] Rb & GPS DO comparison

[k.igor at comcast.net]

The drift rate of 1e-11 per month  or so is regarded after one month of conituous operation. The first month after turn-on is different. It usually takes few days, sometimes couple weeks to reach the final drift rate. After that it is pretty much constant slope. Every time you turn off the clock and then turn i t on again, depends on the duration of off time, the frequency will drift initially at higher rate. It takes time to Rubidium atoms to reach equilibrium position in the cloud inside the resonance cell. When you turn the unit off, the atoms of rubidium (which is metal alk ali by the way) will fall down (gravity) and form little metal drop on the bottom of the cell. When you turn it on, the cell is heated and the atoms evaporate and go into the cloud form. By the way, ambient temperature variations have much higher effect on frequency than just aging. Magnetic fields are also detrimental. Don't place it in close proximity to CRT monitors or dynamic speakers. 



Igor, N1YX 



----- Original Message -----


From: "Tony Estep" <esteptony at gmail.com> 
To: elecraft at mailman.qth.net 
Sent: Thursday, July 21, 2011 11:33:54 AM 
Subject: Re: [Elecraft] Rb & GPS DO comparison 

On Wed, Jul 20, 2011 at 7:08 PM, Igor Kosvin <k.igor at comcast.net> wrote: 

> ...aging drift - better than 1e-11 per month. Useful life of LPRO - usually 
> 15 years. 
> Make your math how much it drifts over life.... 

=========== 
An interesting question. If the drift is always in the same direction, you 
get the (apparently) obvious answer. If, at the other extreme, each month's 
drift is independent of the previous month's, then the expected frequency at 
the end will be described by a Gaussian distribution with mean = the 
starting point, and standard deviation scaled by the square root of the 
number of months. In practice, one would expect some serial correlation 
between monthly drifts, so a bias would be added to the expected mean. 

Tony KT0NY 
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