# Usrp x310 LTE support, with/without external clock

**URL:** <https://www.ruby-forum.com/t/usrp-x310-lte-support-with-without-external-clock/234833>\
**Category:** GNU Radio\
**Created:** [October 10, 2014, 4:26pm UTC](https://www.ruby-forum.com/t/usrp-x310-lte-support-with-without-external-clock/234833 "2014-10-10T16:26:49Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![addis\_a](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/c4cdca/32.png) [@addis\_a](https://www.ruby-forum.com/u/addis_a)\
**Post date:** [October 10, 2014, 4:26pm UTC](https://www.ruby-forum.com/t/usrp-x310-lte-support-with-without-external-clock/234833/1 "2014-10-10T16:26:49Z")

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I’m new to gnuradio and sdr. I’m looking to use a x310 usrp in an lte  
project.  
I have read it can support a 184.32MHz clock frequency  
which is great for LTE and a sample  
rate of 30.72MHz.  
I have looked at the uhd source code.  
I get the impression that the lte frequencies can only be supported  
if you use an external clock,  
I guess this means, external reference clock or Gspdo…  
I haven’t found anything in my googling, which clarifies the situation.

I liked to start withe the basic x310 and a daughter board  
, for example the sbx and add a gspdo  
etc… at a later date.

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**Author:** ![paul](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/bbe5ce/32.png) [@paul](https://www.ruby-forum.com/u/paul)\
**Post date:** [October 10, 2014, 5:14pm UTC](https://www.ruby-forum.com/t/usrp-x310-lte-support-with-without-external-clock/234833/2 "2014-10-10T17:14:44Z")

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Hi Paul,

in (maint branch) host/lib/usrp/x300/x300\_clock\_ctrl.cpp,  
set\_master\_clock\_rate(double):  
if(doubles\_are\_equal(\_system\_ref\_rate, 10e6)) {  
if(doubles\_are\_equal(clock\_rate, 184.32e6)) {  
/\* 10MHz reference, 184.32 MHz master clock out, NOT Zero  
Delay. \*/  
clocking\_mode = m10M\_184\_32M\_NOZDEL;  
}  
[…]

Since the m10M\_184\_32M\_NOZDEL-case further down seems implemented, I’d  
expect that to work.

Greetings,  
Marcus

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**Author:** ![paul](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/bbe5ce/32.png) [@paul](https://www.ruby-forum.com/u/paul)\
**Post date:** [October 10, 2014, 6:35pm UTC](https://www.ruby-forum.com/t/usrp-x310-lte-support-with-without-external-clock/234833/3 "2014-10-10T18:35:19Z")

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Hi Paul,

On Fri, Oct 10, 2014 at 7:19 AM, Paul C. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)  
wrote:

> I’m new to gnuradio and sdr. I’m looking to use a x310 usrp in an lte project.  
> I have read it can support a 184.32MHz clock frequency  
> which is great for LTE and a sample  
> rate of 30.72MHz.  
> I have looked at the uhd source code.  
> I get the impression that the lte frequencies can only be supported  
> if you use an external clock,  
> I guess this means, external reference clock or Gspdo..

184.32 MHz is supported without external referencing. A wide range of  
X310 users are running at that rate both with and without using  
supplemental reference sources.

-TT

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<div class="post-metadata">

**Author:** ![paul](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/bbe5ce/32.png) [@paul](https://www.ruby-forum.com/u/paul)\
**Post date:** [October 10, 2014, 7:47pm UTC](https://www.ruby-forum.com/t/usrp-x310-lte-support-with-without-external-clock/234833/4 "2014-10-10T19:47:10Z")

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On 10/10/2014 06:34 PM, Tom T. wrote:

> 184.32 MHz is supported without external referencing. A wide range of  
> X310 users are running at that rate both with and without using  
> supplemental reference sources.

You can init your device with master\_clock\_rate=184.32e6 to get your  
desired rate.

M

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<div class="post-metadata">

**Author:** ![paul](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/bbe5ce/32.png) [@paul](https://www.ruby-forum.com/u/paul)\
**Post date:** [November 12, 2014, 9:42am UTC](https://www.ruby-forum.com/t/usrp-x310-lte-support-with-without-external-clock/234833/5 "2014-11-12T09:42:27Z")

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Thank you for the replies. I succeeded in using a clock rate of  
184.32Mhz and  
a sample rate of 30.72MHz.

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