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

[Marcus Müller]

Dear Khalid,

the RS232 connection, as you've noticed, is necessary for detection. Without being detected, the GPSDO can still supply a PPS (and 10 MHz clock) over the coax connectors – however, I'm not even sure they will discipline those correctly when not initialized via RS232 by UHD.

Why would you want to unplug RS232?

Best regards,
Marcus

On 03.05.2016 18:02, 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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