[time-nuts] FS740 Thoughts?

[Matt Huszagh]

Hi,

I'm curious to hear people's thoughts on the SRS FS740
(https://www.thinksrs.com/products/fs740.html) as a lab frequency
standard. The phase noise performance of the OCXO and Rb options seem
quite good (the same specs apparently apply during GPS disciplining too)

| offset |   TCXO   | OCXO/Rb  |
| (Hz)   | (dBc/Hz) | (dBc/Hz) |
|--------+----------+----------|
| 1      |   -90    |   -108   |
| 10     |   -104   |   -130   |
| 100    |   -125   |   -144   |
| 1k     |   -142   |   -143   |
| 10k    |   -147   |   -148   |
| 100k   |   -149   |   -149   |
| 1M     |   -153   |   -153   |

as does the Allan deviation (during GPS disciplining)

| time interval (s) | TCXO  | OCXO  |  Rb   |
|-------------------+-------+-------+-------|
| 0.01              | 1E-10 | 2E-11 | 2E-11 |
| 0.1               | 4E-11 | 4E-12 | 4E-12 |
| 1                 | 3E-11 | 2E-12 | 1E-11 |
| 10                | 1E-10 | 2E-12 | 6E-12 |
| 100               | 6E-11 | 2E-12 | 1E-12 |
| 1k                | 6E-12 | 3E-12 | 1E-12 |
| 10k               | 6E-13 | 6E-13 | 3E-13 |
| 100k              | 6E-14 | 6E-14 | 3E-14 |
| 1M                | 5E-15 | 5E-15 | 3E-15 |

(I used the typical performance plots for the phase noise and Allan
deviation data)

The OCXO does not exhibit the the hump around 2s seen by the rubidium
oscillator option (PRS10) and therefore could be seen as better in
applications not requiring the better holdover performance by the Rb.

It also provides a pulse output with jitter < 50 ps RMS that could be
used as a PPS signal. It can also provide a low noise 100 MHz output
signal and can act as a frequency counter and DDS with high resolution
and accuracy. And it comes with the schematics! But.... it's definitely
not cheap. Other thoughts/opinions?

Matt