[time-nuts] Re: FS740 Thoughts?

[ew]

I have been looking at it for years had an email conversation with the designer and Bob. This box is not intended for time nuts and does sell very well, price has gone up over 20 percent.  It would be nice if one could use an external OCXO or Rb and using the Internet interface and have SRS download a Filter Time Constant for a fee based on data submitted. No deal.                                                                                                                                               Bert Kehren                                                                                                                                                                                                                                                                                          

In a message dated 11/17/2021 9:09:42 AM Eastern Standard Time, k8yumdoober at gmail.com writes:Â 
I think that before one places much faith in the ADEV data, it's important
to understand the thermal environment in which the tests were conducted,
compared to your own thermal environment.  The tests were likely to have
been performed in a well-stabilized ambient temperature, to make them
look good.  But your own results may be a lot worse due to HVAC cycling
etc.

One way to reduce such effects is to make the GPS locking loop quite fast,
but doing so is at the cost of the disciplines oscillator's being yanked
around
in phase by "GPS noise", which is really quite awful.  At the other
extreme,
(long locking loop time constant) one largely escapes GPS noise, but finds
that his system has essentially become an expensive thermometer.  So I favor
the use of a GPS-disciplined Rb for critical work (or an active H-maser if
you're
really rich).

I'm presently crutching along with a manually-disciplined surplus PRS-10,
but
am looking for a good excuse to get a factory new lockable unit.

Aha:Â  KB8TQ's note just came in;Â  we're saying about the same thing- I'm
just
wordier.

Dana  K8YUM




On Tue, Nov 16, 2021 at 11:59 PM Matt Huszagh <huszaghmatt at gmail.com> wrote:

> 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)Â  | (dBc/Hz) | (dBc/Hz) |
> |--------+----------+----------|
> | 1Â  Â  Â  |Â  -90Â  Â  |Â  -108Â  |
> | 10Â  Â  |Â  -104Â  |Â  -130Â  |
> | 100Â  Â  |Â  -125Â  |Â  -144Â  |
> | 1k    |  -142  |  -143  |
> | 10k    |  -147  |  -148  |
> | 100k  |  -149  |  -149  |
> | 1MÂ  Â  |Â  -153Â  |Â  -153Â  |
>
> as does the Allan deviation (during GPS disciplining)
>
> | time interval (s) | TCXO  | OCXO  |  Rb  |
> |-------------------+-------+-------+-------|
> | 0.01Â  Â  Â  Â  Â  Â  Â  | 1E-10 | 2E-11 | 2E-11 |
> | 0.1Â  Â  Â  Â  Â  Â  Â  | 4E-11 | 4E-12 | 4E-12 |
> | 1Â  Â  Â  Â  Â  Â  Â  Â  | 3E-11 | 2E-12 | 1E-11 |
> | 10Â  Â  Â  Â  Â  Â  Â  Â  | 1E-10 | 2E-12 | 6E-12 |
> | 100Â  Â  Â  Â  Â  Â  Â  | 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 |
> | 1MÂ  Â  Â  Â  Â  Â  Â  Â  | 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
> _______________________________________________
> time-nuts mailing list -- time-nuts at lists.febo.com -- To unsubscribe send
> an email to time-nuts-leave at lists.febo.com
> To unsubscribe, go to and follow the instructions there.
>
_______________________________________________
time-nuts mailing list -- time-nuts at lists.febo.com -- To unsubscribe send an email to time-nuts-leave at lists.febo.com
To unsubscribe, go to and follow the instructions there.