Re: [Discuss-gnuradio] [USRP-users] minimum PPS voltage for N200

[mleech]

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, <address@hidden> 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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