On 09/01/2020 11:30 AM, Christopher Flood wrote:
Shape is a sinusoid. Vrms going into a 1 megaohm scope is 1.4V, so I
would expect that to be ~.7V going into a 50 ohm load (the SDR), which
I believe is under the max power requirement for the external
reference of the N310.
-Chris
The notes suggest that a square-wave will produce lower phase-noise, but
a sinusoid is also acceptable, and your VP-P should also be
acceptable for the LMK04828 master clock PLL chip that is used in the
N310.
Have you looked at the output spectrum of your Rb clock? The two that I
have had to be "cleaned up" before being used, because
there are typically fairly loud output spurs on "raw" Rb clocks, and
there's no input filtering on the N310.
On Tue, Sep 1, 2020 at 9:26 AM Marcus D Leech <[email protected]
<mailto:[email protected]>> wrote:
What are the output parameters of your Rb reference? Signal
amplitude and shape, etc.
Sent from my iPhone
> On Sep 1, 2020, at 11:18 AM, Christopher Flood via USRP-users
<[email protected] <mailto:[email protected]>>
wrote:
>
>
> Hi all,
>
> Sorry if this is coming through twice - I sent it once before I
subscribed to the list, but didn't know if it went through or not!
(I didn't see it in the archives...)
>
> -------
>
> I'm having some trouble using an external reference with the
Ettus N310. The reference I am using is a FS725 Rubidium Frequency
Standard.
>
> To test the difference between the internal clock and the
external reference, I transmitted a 10MHz signal from the Ettus
N310 with and without the external reference. Using just the
internal clock of the SDR, the 10MHz signal slowly wanders with
respect to the 10MHz signal from the Rubidium Frequency Standard
as seen on an oscilloscope. This is to be expected since the
stability of the internal clock in the SDR is worse than the
Rubidium Frequency Standard.
>
> However, when I connect the 10MHz signal from the Rubidium to
the external reference of the N310 and tell the N310 to use the
external reference, the 10MHz signal that the N310 generates
wanders much faster with respect to the 10MHz signal from the
Rubidium. This is opposite of what I believe should happen,
assuming the N310 is truly using the external reference signal.
>
> Have any of you experienced this or have any tips as to what
might be going on?
>
> Thanks!
>
> -Chris
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