# Is the LimeSDR refclock output programmable?

**URL:** <https://discourse.myriadrf.org/t/is-the-limesdr-refclock-output-programmable/5985>\
**Category:** LimeSDR\
**Created:** [15 April 2020 20:43 UTC](https://discourse.myriadrf.org/t/is-the-limesdr-refclock-output-programmable/5985 "2020-04-15T20:43:47Z")\
**Posts on this page:** 5\
**Page:** 1

<div class="post-metadata">

**Author:** ![DF7CB](https://yyz2.discourse-cdn.com/flex034/user_avatar/discourse.myriadrf.org/df7cb/32/3333_2.png) [@DF7CB](https://discourse.myriadrf.org/u/DF7CB)\
**Post date:** [15 April 2020 20:43 UTC](https://discourse.myriadrf.org/t/is-the-limesdr-refclock-output-programmable/5985/1 "2020-04-15T20:43:47Z")

</div>

I’m trying to get my LimeSDR USB set up for QO100 satellite operation. As the LNB in the sat dish has only a simple XCO built-in it will be necessary to feed an external clock of around 27 MHz into the LNB.

As the LimeSDR has a refclock output, I had the idea to tell the LimeSDR to put 27 MHz on that output. But it seems hardwired to 30.72 MHz. Is there a way out?

Thanks,  
Christoph

---

<div class="post-metadata">

**Author:** ![N0YKG](https://avatars.discourse-cdn.com/v4/letter/n/3bc359/32.png) [@N0YKG](https://discourse.myriadrf.org/u/N0YKG)\
**Post date:** [16 April 2020 11:49 UTC](https://discourse.myriadrf.org/t/is-the-limesdr-refclock-output-programmable/5985/2 "2020-04-16T11:49:48Z")

</div>

Stupid question: can you just generate the needed clock signal on one of the TX ports of the Lime?

---

<div class="post-metadata">

**Author:** ![DF7CB](https://yyz2.discourse-cdn.com/flex034/user_avatar/discourse.myriadrf.org/df7cb/32/3333_2.png) [@DF7CB](https://discourse.myriadrf.org/u/DF7CB)\
**Post date:** [16 April 2020 16:52 UTC](https://discourse.myriadrf.org/t/is-the-limesdr-refclock-output-programmable/5985/3 "2020-04-16T16:52:58Z")

</div>

Yeah I guess that’s a pretty smart idea.

---

<div class="post-metadata">

**Author:** ![andrewback](https://avatars.discourse-cdn.com/v4/letter/a/22d042/32.png) [@andrewback](https://discourse.myriadrf.org/u/andrewback)\
**Post date:** [18 April 2020 08:09 UTC](https://discourse.myriadrf.org/t/is-the-limesdr-refclock-output-programmable/5985/4 "2020-04-18T08:09:33Z")

</div>

Just bear in mind that you can’t have two processes open the SDR at the same time, so I suspect that whatever software you use for the RX will need to set up the transmit stream also.

Nice idea BTW!

---

<div class="post-metadata">

**Author:** ![DF7CB](https://yyz2.discourse-cdn.com/flex034/user_avatar/discourse.myriadrf.org/df7cb/32/3333_2.png) [@DF7CB](https://discourse.myriadrf.org/u/DF7CB)\
**Post date:** [1 May 2020 16:18 UTC](https://discourse.myriadrf.org/t/is-the-limesdr-refclock-output-programmable/5985/5 "2020-05-01T16:18:02Z")

</div>

After actually trying, it turned out it doesn’t work because there’s only one TX PLL for both ports, so the actual TX frequency and the generated clock signal can’t be more than some MHz apart. Pity. ☹