# GPSDO detection in B200

**URL:** <https://www.ruby-forum.com/t/gpsdo-detection-in-b200/230259>\
**Category:** GNU Radio\
**Created:** [June 6, 2014, 8:20pm UTC](https://www.ruby-forum.com/t/gpsdo-detection-in-b200/230259 "2014-06-06T20:20:31Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![jason\_sam](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/7993a0/32.png) [@jason\_sam](https://www.ruby-forum.com/u/jason_sam)\
**Post date:** [June 6, 2014, 8:20pm UTC](https://www.ruby-forum.com/t/gpsdo-detection-in-b200/230259/1 "2014-06-06T20:20:31Z")

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Hi, How is the detection of GPSDO done in B200 ?  
I see that UHD tries to detect GPSDO every time I use B200 but what is  
it looking for?  
How to force switching between internal, external and GPSDO clock ? I  
have GPSDO installed but sometimes I want to force another clock source.  
Also is there some more detailed description of what the LED’s  
LED802/LED803 mean (especially LED802)?

---

<div class="post-metadata">

**Author:** ![rlorimor](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/96bed5/32.png) [@rlorimor](https://www.ruby-forum.com/u/rlorimor)\
**Post date:** [June 6, 2014, 8:22pm UTC](https://www.ruby-forum.com/t/gpsdo-detection-in-b200/230259/2 "2014-06-06T20:22:53Z")

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On 06/06/2014 02:19 PM, Robert L. wrote:

> Hi, How is the detection of GPSDO done in B200 ?  
> I see that UHD tries to detect GPSDO every time I use B200 but what is it  
> looking for?  
> How to force switching between internal, external and GPSDO clock ? I have GPSDO  
> installed but sometimes I want to force another clock source.  
> Also is there some more detailed description of what the LED’s LED802/LED803  
> mean (especially LED802)?
> 
> * * *
> 
> Discuss-gnuradio mailing list  
> [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)  
> [Discuss-gnuradio Info Page](https://lists.gnu.org/mailman/listinfo/discuss-gnuradio)

I believe it just looks for messages from the NMEA serial port on the  
GPSDO.

Also, you can select different clock sources when you instantiate a UHD  
source/sink block in GRC. There’s a drop-down menu.

If you aren’t programming using GRC, you can use what it _does_ generate  
in the Python as a template for your own code.

–  
Marcus L.  
Principal Investigator  
Shirleys Bay Radio Astronomy Consortium

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