Hi,
On 09/24/2017 02:30 PM, Bob kb8tq wrote:
Hi
On Sep 23, 2017, at 9:39 PM, Hal Murray <[email protected]> wrote:
[email protected] said:
If the main use is feeding test gear (and not direct synthesis) an Rb may do
pretty well. Most instruments assume a dirty reference signal and clean it
up internally.
What's the bandwidth on the typical cleanup PLL? How well does that match
the noise from a Rb?
It’s like any other PLL with noise involved. You look at the noise of the Rb,
the
noise of the particular cleanup oscillator, and your system requirements. In
some
cases that comes out to a few seconds. For Time Nut grade with a really good
OCXO you are at some pretty long numbers.
If the Rb starts at 2x10^-11 at 1 second and goes down by square root tau: At
100 seconds you are at 2x10^12. Still not as good as a really good OCXO. At
10,000 seconds you might get to 2x10^-13 (but probably will not). Your OCXO
likely will climb out of the “parts in 10^-13” range before 10,000 seconds.
Lots of fun.
Once up on a time, you could order the OSA cesiums width different
oscillators, essentially to buy into different balances between
oscillator cost and performance. The time constant is adapter with
regards to oscillator type, as the trade off shifts.
I can't recall any other cesium or rubidium that did this, but HP
upgraded oscillators at one point for this reason too.
Cheers,
Magnus
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