What you're going to need to do is provide the *simplest* flow-graph
that demonstrates the issue, rather than requiring the community to
debug your entire end-to-end setup.
Also a diagram of your setup showing the RF and 1PPS and 10MHz paths.
On 2016-05-03 15:39, khalid.el-darymli wrote:
> Thanks again Marcus. I really appreciate your help.
>
> I am setting Ref Clock / PPS to external, etc. I get the syncing to work
> properly around a year ago. Since then, we made various changes and I think
> one or more change may be causing the issue. Among the changes are: buy N200
> units with a new revision (could that be a problem when syncing?), upgrading
> GNU Radio / UHD, enabling Rs 232 echoing in the GPSDO, etc.
>
> Similar to my last year tests (I entirely unplugged the RS 232 cable), and
> now it is not detected as an Internal GPSDO. However, I am still having issue
> syncing the two motherboards.
>
> Attached are two figures for the phase drift between Rx1 vs. Rx2, and Rx1 vs.
> Rx3. This was generated through splitting the Tx and looping it back to the
> Rx's. Signal processing was done properly (for dechirping, downsamplng, etc).
> My application is LFMCW radar, so each 490 samples in the attachment
> represents one sweep, and sweeping was done continuously.
>
> angle(Rx1./Rx2) looks great. As to angle(Rx1./Rx3), I would expect a linear
> phase offset between different motherboards. However, as .shown in the
> attachment, Rx1 vs. Rx3 has weird phase spikes. I think this shows that, for
> some reason, the Tx is not properly synced with the second motherboard. Any
> ideas on what might be causing this issue?
>
> I am using Starttech Ethernet Adapter (ST1000SPEX4). The problem I have with
> this card is that it won't turn AUTONEG off, it is always on. Could this
> cause the problem?
>
> I tried this on two different Ubuntu machines, with similar results as shown
> in the attachment.
>
> For the first machine,
>
> UBUNTU 14.04 LTS
> linux; GNU C++ version 4.8.2; Boost_105400; UHD_003.008.002-80-ge28d7844
>
> For the second machine,
> UBUNTU 14.04 LTS
> linux; GNU C++ version 4.8.2; Boost_105400; UHD_003.008.000-46-g5b706d29
>
> I'll highly appreciate any suggestions to solve this problem.
>
> Thank you.
>
> Best wishes,
> khalid
>
> On Tue, May 3, 2016 at 1:45 PM, <[email protected]> wrote:
>
> The only way the USRP knows that there's a GPSDO present is if the serial
> data from the GSPDO is validated. If it doesn't see that data, it concludes
> that there's no (internal) GPSDO present.
>
> There is no concept of "external GPSDO" -- only that *something* is providing
> 10MHz and 1PPS externally. The N2xx has no idea what that might be.
>
> You should set both 1PPS and 10MHz clock to "external" in your flow-graph.
> The only time "GPSDO" is used is when you have a properly-installed
> internally-mounted, GPSDO unit.
>
> On 2016-05-03 12:02, khalid.el-darymli wrote:
>
> Thanks Marcus.
>
> OK, I'm communicating with the external Firefly-1A GPSDO unit using an RS 232
> cable. I am able to do so after enabling echoing on RS 232 from the GPSDO.
> Would that be a problem? Do I need to completely disable the RS 232 echoing,
> even while the RS 232 cable is completely unplugged?
>
> When the RS 232 cable is plugged-in, N200 DETECTs it as an INTERNAL GPSDO.
> When I completely unplug the RS 232 cable on both ends, I am not getting any
> messages for detecting neither external nor internal GPSDO. It only shows the
> following in the terminal for both N200 devices,
>
> (1) catch time transition at pps edge (2) set time next pps (synchronously).
>
> khalid
>
> On Tue, May 3, 2016 at 12:20 PM, <[email protected]> wrote:
>
> The PPS input is conditioned with a:
>
> http://www.ti.com/product/SN74AUP1T57/description
>
> Looks to me like it should work just fine.
>
> On 2016-05-03 10:23, khalid.el-darymli via USRP-users wrote:
>
> Hi,
>
> I'll appreciate any help on the following. According to the link below [1],
> the PPS voltage for N200 should be in the range [3.3, 5] V p-p.
> [1] http://files.ettus.com/manual/page_usrp2.html#usrp2_hw_leds
>
> I am getting a PPS signal through fan-outs from an external Firefly-1A GPSDO.
> I measured the output PPS voltage using a scope, and it is 2.52 V P-P
> (terminated with 50 ohms).
>
> Would this relatively low PPS voltage work for N200? I am having a problem
> syncing two N200 units (2 LFRX/ 1 LFTX ), and I am not sure if this would be
> the cause?
>
> Thank you.
>
> Best wishes,
> Khalid
>
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