[time-nuts] a link to a explanation of Rb vs Cs?

Bob kb8tq kb8tq at n1k.org
Wed Apr 12 07:17:40 EDT 2017


If you take a look at the standard weekly publications, the GPS system runs on Rb’s.
There is always one sat that has a Cs turned on. That’s been true as long as they
have been running the system. The simple answer for that choice is that the Rb’s
are easier to predict (better short term to medium term performance). 

The Cs standards were originally on board to allow operation in the event that the ground control
system was unable to upload to the constellation. There also was concern in the 80’s 
about the reliability of the Rb’s. The configuration has stayed the same, despite the
Rb’s being the main standard used. 

Number of standards on board in the block IIF sats was 2 Rb’s and 2 Cs’s. That is a 
petty typical “redundant” approach. 


> On Apr 12, 2017, at 2:41 AM, Hal Murray <hmurray at megapathdsl.net> wrote:
> jimlux at earthlink.net said:
>> If there's nothing folks are aware of, I'll probably see if I can find  some
>> nice schematic pictures of a Cs Beam, a gas cell, and an Hg ion  trap, and
>> then a AVAR plot or something. 
> I think the GPS satellites have 3 Cs and 2 Rbs.  There might be an 
> interesting story about why they decided to split their eggs into two baskets.
> -- 
> These are my opinions.  I hate spam.
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