Hello Jorge,
The Octoclock is sold in two versions, one with an internal GPSDO and one
that requires an external source.
The X310 and X300 both do not support daisy chaining. There are a few
issues with it, one of the key ones being propagation delay. If the 1PPS
signal was passed from one unit to the next again and again it would arrive
at the different USRPs at different times, ruining synchronization.
The configuration should work with one of the X310s supplying the 10 MHz
and 1 PPS. However it would be better to have the Octoclock's 10 MHz and
1PPS outputs connected to all four of the X310s. The X310 will always
output it's signals so can still be used as the source but by using the
external reference on all USRPs the 1PPS signals will be aligned at all
units rather than having the master be earlier than the others due to
propagation delays.
Do you see the PPS light flashing on the Octoclock? What do the other
lights show?
Which USRP is failing to synchronize? If you only try to synchronize the
slave USRPs does that work?
Regards,
Derek
On Mon, Aug 7, 2017 at 3:28 PM, Jorge Chen via USRP-users <
usrp-users@lists.ettus.com> wrote:
> Hi all
>
>
>
> I’d like to build up 8X8 MIMO system using 4 USRP X310.
>
> To synchronize time&freq. between all of them, I used to use a function
> generator to feed both 1 PPS and 10 MHz reference clock to them.
>
> Today, I got an Octoclock which I thought it is able to provide both
> synchronization signal, but it is said that “For the OctoClock, there is
> no internal timing or clocking source, so the OctoClock will always use
> external 10 MHz and 1 PPS sources, regardless of the position of the switch.”
> in the UHD manual.
>
>
>
> So, I plan to use one of the X310 to feed the synchronization signal to
> the Octoclock REF&PPS input and connect other X310s to the REF&PPS output,
> like the block diagram below.
>
>
>
> [image: 內置圖片 1]
>
> 1.
>
> I use the LTS version of UHD (3.9.6).
>
> And I use the commands like:
>
> //Lock mboard clocks
>
> tx_usrp->set_clock_source("internal",0);
>
> tx_usrp->set_clock_source("external",1);
>
> But it always show the error message:
>
> Error: RuntimeError: Reference Clock PLL failed to lock to external source.
>
>
>
> I wonder if the commands or my thought were wrong or this function is not
> supported?Because I found some discussions (March, 2017) in the mailing
> list talked about the X310 is not supported for daisy-chaining. By the way,
> is X300 not supported neither?
>
>
>
>
>
> 2.
>
> The other problem is that when I use a terminator to terminate the TX/RX
> port, I can still discover the signal through the spectrum analyzer by
> connecting an antenna. Is the signal leaked from somewhere? And how to
> prevent it?
>
>
>
>
>
> Thanks in advance!
>
> Jorge
>
>
>
>
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>
>
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