I have not looked at the output spectrum of the Rb, I kind of just assumed it would be okay since it's the most stable oscillator that we have in our lab. I can take a look at the spectrum and report back.
If I do see output spurs, do you have any suggestions / tips on cleaning up the signal to the point where it would work as an external reference? -Chris On Tue, Sep 1, 2020 at 10:06 AM Marcus D. Leech <[email protected]> wrote: > 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]> > 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]> 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 >> > _______________________________________________ >> > USRP-users mailing list >> > [email protected] >> > >> http://secure-web.cisco.com/1nWDwD0LbO77QthlIKVs0gyhEI4cVA_IfTj4rvvFSL4qWjw_BKsjarpNVGUg1WSCn9mLxWoszHiy1EL4wQBcyjVSZlchr4oAdnfbUKsQurDlSMkQ3xes5nNVfRZbMo1K_tC57_jfBijc7k1IJEeJI4eGE5lp6Hvxm5TrWP7xYZJN3Rno2PLqMojzmmGUON3j_FwZI5DrM1IRJJOp4zugqAiDWJkDCb9_EmunfDHehAlAUGJMMDQ9fvhujOQ6RMQSye2luXmluRt_L10jyNP6kk-a7ojOTF1lgm_5ZcB9LpYVMPx8JEbY8_VIcwrlrC-n2XC4dn41AUQyHPf47I3DWWUSBZZGaTEgad3YzhpIvd0Mk3XAPpGfdyAPTH6kEW-xpRHOSnTArwXMSBHYc-Wy_utBs6L16LMlPST1Q65z9FcHKQbE-3AjZkQbUl--HGEeSu2HcZH89_ufKsucuflnBKQ/http%3A%2F%2Flists.ettus.com%2Fmailman%2Flistinfo%2Fusrp-users_lists.ettus.com >> >> >
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